[FFmpeg-devel] [PATCHv2 1/4] lavc/h263dsp: add DCT dequantisation function

[FFmpeg-devel] [PATCHv2 1/4] lavc/h263dsp: add DCT dequantisation function

[Rémi Denis-Courmont]

To preserve the alignment promise of the block base address, we pass
the start offset separately (it is either 0 or 1).

Note that optimised implementations of this function will be taken into
actual use if MpegEncContext.dct_unquantize_h263_{inter,intra} are *not*
overloaded by existing optimisations.
---
 libavcodec/h263dsp.c | 17 +++++++++++++++++
 libavcodec/h263dsp.h |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
index 6a13353499..eb990f27bd 100644
--- a/libavcodec/h263dsp.c
+++ b/libavcodec/h263dsp.c
@@ -23,6 +23,22 @@
 #include "config.h"
 #include "h263dsp.h"
 
+static void h263_dct_unquantize_c(int16_t *block, size_t start, size_t end,
+                                  int qmul, int qadd)
+{
+    for (size_t i = start; i <= end; i++) {
+        int level = block[i];
+
+        if (level) {
+            if (level < 0)
+                level = level * qmul - qadd;
+            else
+                level = level * qmul + qadd;
+            block[i] = level;
+        }
+    }
+}
+
 const uint8_t ff_h263_loop_filter_strength[32] = {
     0, 1, 1, 2, 2, 3, 3,  4,  4,  4,  5,  5,  6,  6,  7, 7,
     7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12
@@ -116,6 +132,7 @@ static void h263_v_loop_filter_c(uint8_t *src, int stride, int qscale)
 
 av_cold void ff_h263dsp_init(H263DSPContext *ctx)
 {
+    ctx->h263_dct_unquantize = h263_dct_unquantize_c;
     ctx->h263_h_loop_filter = h263_h_loop_filter_c;
     ctx->h263_v_loop_filter = h263_v_loop_filter_c;
 
diff --git a/libavcodec/h263dsp.h b/libavcodec/h263dsp.h
index 2dccd23392..93c128c9ac 100644
--- a/libavcodec/h263dsp.h
+++ b/libavcodec/h263dsp.h
@@ -24,6 +24,8 @@
 extern const uint8_t ff_h263_loop_filter_strength[32];
 
 typedef struct H263DSPContext {
+    void (*h263_dct_unquantize)(int16_t *block /* align 16 */, size_t offset,
+                                size_t len, int mul, int add);
     void (*h263_h_loop_filter)(uint8_t *src, int stride, int qscale);
     void (*h263_v_loop_filter)(uint8_t *src, int stride, int qscale);
 } H263DSPContext;
-- 
2.45.1

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[FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

---
 libavcodec/mpegvideo.c | 30 +++++-------------------------
 1 file changed, 5 insertions(+), 25 deletions(-)

diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
index 7af823b8bd..fa25d14970 100644
--- a/libavcodec/mpegvideo.c
+++ b/libavcodec/mpegvideo.c
@@ -201,7 +201,7 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
 static void dct_unquantize_h263_intra_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
+    int qmul, qadd;
     int nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
@@ -219,23 +219,13 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
     else
         nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
 
-    for(i=1; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    s->h263dsp.h263_dct_unquantize(block, 1, nCoeffs, qmul, qadd);
 }
 
 static void dct_unquantize_h263_inter_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
+    int qmul, qadd;
     int nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0);
@@ -244,18 +234,7 @@ static void dct_unquantize_h263_inter_c(MpegEncContext *s,
     qmul = qscale << 1;
 
     nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
-
-    for(i=0; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    s->h263dsp.h263_dct_unquantize(block, 0, nCoeffs, qmul, qadd);
 }
 
 
@@ -275,6 +254,7 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
 static av_cold int dct_init(MpegEncContext *s)
 {
     ff_blockdsp_init(&s->bdsp);
+    ff_h263dsp_init(&s->h263dsp);
     ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
     ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
 
-- 
2.45.1

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Andreas Rheinhardt]

Rémi Denis-Courmont:
> ---
>  libavcodec/mpegvideo.c | 30 +++++-------------------------
>  1 file changed, 5 insertions(+), 25 deletions(-)
> 
> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> index 7af823b8bd..fa25d14970 100644
> --- a/libavcodec/mpegvideo.c
> +++ b/libavcodec/mpegvideo.c
> @@ -201,7 +201,7 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
>  static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>                                    int16_t *block, int n, int qscale)
>  {
> -    int i, level, qmul, qadd;
> +    int qmul, qadd;
>      int nCoeffs;
>  
>      av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
> @@ -219,23 +219,13 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>      else
>          nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
>  
> -    for(i=1; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    s->h263dsp.h263_dct_unquantize(block, 1, nCoeffs, qmul, qadd);
>  }
>  
>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>                                    int16_t *block, int n, int qscale)
>  {
> -    int i, level, qmul, qadd;
> +    int qmul, qadd;
>      int nCoeffs;
>  
>      av_assert2(s->block_last_index[n]>=0);
> @@ -244,18 +234,7 @@ static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>      qmul = qscale << 1;
>  
>      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> -
> -    for(i=0; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    s->h263dsp.h263_dct_unquantize(block, 0, nCoeffs, qmul, qadd);
>  }
>  
>  
> @@ -275,6 +254,7 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
>  static av_cold int dct_init(MpegEncContext *s)
>  {
>      ff_blockdsp_init(&s->bdsp);
> +    ff_h263dsp_init(&s->h263dsp);
>      ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
>      ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
>  

This approach will make H.261 use a h263dsp function which is a misnomer
and will lead to undefined references if no H.263 decoder or encoder is
enabled.

- Andreas

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le sunnuntaina 9. kesäkuuta 2024, 19.13.54 EEST Andreas Rheinhardt a écrit :
> Rémi Denis-Courmont:
> > ---
> > 
> >  libavcodec/mpegvideo.c | 30 +++++-------------------------
> >  1 file changed, 5 insertions(+), 25 deletions(-)
> > 
> > diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> > index 7af823b8bd..fa25d14970 100644
> > --- a/libavcodec/mpegvideo.c
> > +++ b/libavcodec/mpegvideo.c
> > @@ -201,7 +201,7 @@ static void
> > dct_unquantize_mpeg2_inter_c(MpegEncContext *s,> 
> >  static void dct_unquantize_h263_intra_c(MpegEncContext *s,
> >  
> >                                    int16_t *block, int n, int qscale)
> >  
> >  {
> > 
> > -    int i, level, qmul, qadd;
> > +    int qmul, qadd;
> > 
> >      int nCoeffs;
> >      
> >      av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
> > 
> > @@ -219,23 +219,13 @@ static void
> > dct_unquantize_h263_intra_c(MpegEncContext *s,> 
> >      else
> >      
> >          nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
> > 
> > -    for(i=1; i<=nCoeffs; i++) {
> > -        level = block[i];
> > -        if (level) {
> > -            if (level < 0) {
> > -                level = level * qmul - qadd;
> > -            } else {
> > -                level = level * qmul + qadd;
> > -            }
> > -            block[i] = level;
> > -        }
> > -    }
> > +    s->h263dsp.h263_dct_unquantize(block, 1, nCoeffs, qmul, qadd);
> > 
> >  }
> >  
> >  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
> >  
> >                                    int16_t *block, int n, int qscale)
> >  
> >  {
> > 
> > -    int i, level, qmul, qadd;
> > +    int qmul, qadd;
> > 
> >      int nCoeffs;
> >      
> >      av_assert2(s->block_last_index[n]>=0);
> > 
> > @@ -244,18 +234,7 @@ static void
> > dct_unquantize_h263_inter_c(MpegEncContext *s,> 
> >      qmul = qscale << 1;
> >      
> >      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> > 
> > -
> > -    for(i=0; i<=nCoeffs; i++) {
> > -        level = block[i];
> > -        if (level) {
> > -            if (level < 0) {
> > -                level = level * qmul - qadd;
> > -            } else {
> > -                level = level * qmul + qadd;
> > -            }
> > -            block[i] = level;
> > -        }
> > -    }
> > +    s->h263dsp.h263_dct_unquantize(block, 0, nCoeffs, qmul, qadd);
> > 
> >  }
> > 
> > @@ -275,6 +254,7 @@ static void gray8(uint8_t *dst, const uint8_t *src,
> > ptrdiff_t linesize, int h)> 
> >  static av_cold int dct_init(MpegEncContext *s)
> >  {
> >  
> >      ff_blockdsp_init(&s->bdsp);
> > 
> > +    ff_h263dsp_init(&s->h263dsp);
> > 
> >      ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
> >      ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
> 
> This approach will make H.261 use a h263dsp function which is a misnomer

In reality, that is an existing problem: the *existing* pair of DCT functions 
for H.263 is provisioned regardless of the codec. Fixing the god object and 
spaghetti anti-patterns in MpegEncContext is way outside the scope of this MR.

> and will lead to undefined references if no H.263 decoder or encoder is
> enabled.

Fair enough, *that* is easy to fix.

-- 
Rémi Denis-Courmont
http://www.remlab.net/



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[FFmpeg-devel] [PATCHv2 3/4] checkasm/h263dsp: test dct_unquantize

[Rémi Denis-Courmont]

---
 tests/checkasm/h263dsp.c | 46 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/tests/checkasm/h263dsp.c b/tests/checkasm/h263dsp.c
index 2d0957a90b..546204cb28 100644
--- a/tests/checkasm/h263dsp.c
+++ b/tests/checkasm/h263dsp.c
@@ -18,13 +18,54 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#include <stdbool.h>
 #include <string.h>
 
 #include "checkasm.h"
 
-#include "libavcodec/h263dsp.h"
+#include "libavutil/avassert.h"
 #include "libavutil/mem.h"
 #include "libavutil/mem_internal.h"
+#include "libavcodec/h263dsp.h"
+#include "libavcodec/mpegvideodata.h"
+
+static uint_fast8_t mpeg_qscale_rnd(void)
+{
+    int n = rnd(), q = (n >> 1) & 31;
+
+    if (n & 1)
+        return ff_mpeg2_non_linear_qscale[q];
+    else
+        return q << 1;
+}
+
+static void check_dct_unquantize(H263DSPContext *ctx, bool intra)
+{
+#define LEN 64
+    LOCAL_ALIGNED_16(int16_t, block0, [LEN]);
+    LOCAL_ALIGNED_16(int16_t, block1, [LEN]);
+    size_t end = rnd() % LEN;
+    const int qscale = mpeg_qscale_rnd();
+    const int qmul = qscale << 1;
+    const int qadd = (rnd() & 1) ? (qscale - 1) | 1 : 0;
+
+    declare_func(void, int16_t *, size_t, size_t, int, int);
+
+    for (size_t i = 0; i < LEN; i++)
+        block1[i] = block0[i] = (rnd() & 1) ? rnd() : 0;
+
+    if (check_func(ctx->h263_dct_unquantize, "h263dsp.dct_unquantize_int%s",
+                   intra ? "ra" : "er")) {
+        av_assert0(end < LEN);
+        call_ref(block0, intra, end, qmul, qadd);
+        call_new(block1, intra, end, qmul, qadd);
+
+        if (memcmp(block0, block1, (end + 1) * sizeof (int16_t)))
+            fail();
+
+        bench_new(block1, intra, LEN, qmul, qadd);
+    }
+}
 
 typedef void (*filter)(uint8_t *src, int stride, int qscale);
 
@@ -56,6 +97,9 @@ void checkasm_check_h263dsp(void)
     H263DSPContext ctx;
 
     ff_h263dsp_init(&ctx);
+    check_dct_unquantize(&ctx, false);
+    check_dct_unquantize(&ctx, true);
+    report("dct_unquantize");
     check_loop_filter('h', ctx.h263_h_loop_filter);
     check_loop_filter('v', ctx.h263_v_loop_filter);
     report("loop_filter");
-- 
2.45.1

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[FFmpeg-devel] [PATCH 4/4] lavc/h263dsp: R-V V dct_unquantize

[Rémi Denis-Courmont]

T-Head C908:
h263dsp.dct_unquantize_inter_c:       5.7
h263dsp.dct_unquantize_inter_rvv_i32: 2.7
h263dsp.dct_unquantize_intra_c:       5.7
h263dsp.dct_unquantize_intra_rvv_i32: 3.0

SpacemiT X60:
h263dsp.dct_unquantize_inter_c:       5.0
h263dsp.dct_unquantize_inter_rvv_i32: 1.2
h263dsp.dct_unquantize_intra_c:       5.0
h263dsp.dct_unquantize_intra_rvv_i32: 1.5
---
 libavcodec/riscv/h263dsp_init.c | 12 +++++++++---
 libavcodec/riscv/h263dsp_rvv.S  | 22 ++++++++++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/libavcodec/riscv/h263dsp_init.c b/libavcodec/riscv/h263dsp_init.c
index 21b536366c..5d73fde865 100644
--- a/libavcodec/riscv/h263dsp_init.c
+++ b/libavcodec/riscv/h263dsp_init.c
@@ -25,6 +25,7 @@
 #include "libavutil/riscv/cpu.h"
 #include "libavcodec/h263dsp.h"
 
+void ff_h263_dct_unquantize_rvv(int16_t *, size_t start, size_t end, int, int);
 void ff_h263_h_loop_filter_rvv(uint8_t *src, int stride, int q);
 void ff_h263_v_loop_filter_rvv(uint8_t *src, int stride, int q);
 
@@ -33,9 +34,14 @@ av_cold void ff_h263dsp_init_riscv(H263DSPContext *c)
 #if HAVE_RVV
     int flags = av_get_cpu_flags();
 
-    if ((flags & AV_CPU_FLAG_RVV_I32) && ff_rv_vlen_least(128)) {
-        c->h263_h_loop_filter = ff_h263_h_loop_filter_rvv;
-        c->h263_v_loop_filter = ff_h263_v_loop_filter_rvv;
+    if (flags & AV_CPU_FLAG_RVV_I32) {
+        if (flags & AV_CPU_FLAG_RVB_ADDR)
+            c->h263_dct_unquantize = ff_h263_dct_unquantize_rvv;
+
+        if (ff_rv_vlen_least(128)) {
+            c->h263_h_loop_filter = ff_h263_h_loop_filter_rvv;
+            c->h263_v_loop_filter = ff_h263_v_loop_filter_rvv;
+        }
     }
 #endif
 }
diff --git a/libavcodec/riscv/h263dsp_rvv.S b/libavcodec/riscv/h263dsp_rvv.S
index 97503d527c..319c51a0bb 100644
--- a/libavcodec/riscv/h263dsp_rvv.S
+++ b/libavcodec/riscv/h263dsp_rvv.S
@@ -20,6 +20,28 @@
 
 #include "libavutil/riscv/asm.S"
 
+func ff_h263_dct_unquantize_rvv, zve32x
+        sub     a2, a2, a1
+        sh1add  a0, a1, a0
+        addi    a2, a2, 1
+1:
+        vsetvli  t0, a2, e16, m4, ta, mu
+        vle16.v  v8, (a0)
+        sub      a2, a2, t0
+        vmv.v.x  v24, a4
+        vmslt.vi v0, v8, 0
+        vneg.v   v24, v24, v0.t
+        vmsne.vi v0, v8, 0
+        vwmul.vx v16, v8, a3
+        vwadd.wv v16, v16, v24, v0.t
+        vncvt.x.x.w v8, v16
+        vse16.v v8, (a0)
+        sh1add  a0, t0, a0
+        bnez    a2, 1b
+
+        ret
+endfunc
+
         .option push
         .option norelax
 func ff_h263_h_loop_filter_rvv, zve32x
-- 
2.45.1

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Re: [FFmpeg-devel] [PATCHv2 1/4] lavc/h263dsp: add DCT dequantisation function

[Rémi Denis-Courmont]

Le sunnuntaina 9. kesäkuuta 2024, 12.27.06 EEST Rémi Denis-Courmont a écrit :
> To preserve the alignment promise of the block base address, we pass
> the start offset separately (it is either 0 or 1).
> 
> Note that optimised implementations of this function will be taken into
> actual use if MpegEncContext.dct_unquantize_h263_{inter,intra} are *not*
> overloaded by existing optimisations.
> ---
>  libavcodec/h263dsp.c | 17 +++++++++++++++++
>  libavcodec/h263dsp.h |  2 ++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
> index 6a13353499..eb990f27bd 100644
> --- a/libavcodec/h263dsp.c
> +++ b/libavcodec/h263dsp.c
> @@ -23,6 +23,22 @@
>  #include "config.h"
>  #include "h263dsp.h"
> 
> +static void h263_dct_unquantize_c(int16_t *block, size_t start, size_t end,
> +                                  int qmul, int qadd)
> +{
> +    for (size_t i = start; i <= end; i++) {

C and R-V V don't care, but for the sake of more constrained SIMD extensions, 
it should be easier to keep intra and inter DCT functions separate.

-- 
Rémi Denis-Courmont
http://www.remlab.net/



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[FFmpeg-devel] [PATCHv3 1/4] lavc/h263dsp: add DCT dequantisation functions

[Rémi Denis-Courmont]

Note that optimised implementations of these functions will be taken
into actual use only if MpegEncContext.dct_unquantize_h263_{inter,intra}
are *not* overloaded by existing optimisations.

---
Compared to version 2, this separates inter and intra functions to
ease writing aligned-dependent optimisations.

---
 libavcodec/h263dsp.c | 24 ++++++++++++++++++++++++
 libavcodec/h263dsp.h |  4 ++++
 2 files changed, 28 insertions(+)

diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
index 6a13353499..1c6cf85a70 100644
--- a/libavcodec/h263dsp.c
+++ b/libavcodec/h263dsp.c
@@ -23,6 +23,28 @@
 #include "config.h"
 #include "h263dsp.h"
 
+static void h263_dct_unquantize_inter_c(int16_t *block, size_t len,
+                                        int qmul, int qadd)
+{
+    for (size_t i = 0; i < len; i++) {
+        int level = block[i];
+
+        if (level) {
+            if (level < 0)
+                level = level * qmul - qadd;
+            else
+                level = level * qmul + qadd;
+            block[i] = level;
+        }
+    }
+}
+
+static void h263_dct_unquantize_intra_c(int16_t *block, size_t len,
+                                        int qmul, int qadd)
+{
+    h263_dct_unquantize_inter_c(block + 1, len - 1, qmul, qadd);
+}
+
 const uint8_t ff_h263_loop_filter_strength[32] = {
     0, 1, 1, 2, 2, 3, 3,  4,  4,  4,  5,  5,  6,  6,  7, 7,
     7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12
@@ -116,6 +138,8 @@ static void h263_v_loop_filter_c(uint8_t *src, int stride, int qscale)
 
 av_cold void ff_h263dsp_init(H263DSPContext *ctx)
 {
+    ctx->h263_dct_unquantize_intra = h263_dct_unquantize_intra_c;
+    ctx->h263_dct_unquantize_inter = h263_dct_unquantize_inter_c;
     ctx->h263_h_loop_filter = h263_h_loop_filter_c;
     ctx->h263_v_loop_filter = h263_v_loop_filter_c;
 
diff --git a/libavcodec/h263dsp.h b/libavcodec/h263dsp.h
index 2dccd23392..0ecbe83314 100644
--- a/libavcodec/h263dsp.h
+++ b/libavcodec/h263dsp.h
@@ -24,6 +24,10 @@
 extern const uint8_t ff_h263_loop_filter_strength[32];
 
 typedef struct H263DSPContext {
+    void (*h263_dct_unquantize_intra)(int16_t *block /* align 16 */,
+                                      size_t len, int mul, int add);
+    void (*h263_dct_unquantize_inter)(int16_t *block /* align 16 */,
+                                      size_t len, int mul, int add);
     void (*h263_h_loop_filter)(uint8_t *src, int stride, int qscale);
     void (*h263_v_loop_filter)(uint8_t *src, int stride, int qscale);
 } H263DSPContext;
-- 
2.45.1

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[FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

---
 libavcodec/mpegvideo.c | 44 ++++++++++--------------------------------
 1 file changed, 10 insertions(+), 34 deletions(-)

diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
index 7af823b8bd..9be0fecc8d 100644
--- a/libavcodec/mpegvideo.c
+++ b/libavcodec/mpegvideo.c
@@ -201,13 +201,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
 static void dct_unquantize_h263_intra_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
-    int nCoeffs;
+    int qmul = qscale << 1;
+    int qadd, nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
 
-    qmul = qscale << 1;
-
     if (!s->h263_aic) {
         block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
         qadd = (qscale - 1) | 1;
@@ -215,47 +213,24 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
         qadd = 0;
     }
     if(s->ac_pred)
-        nCoeffs=63;
+        nCoeffs = 64;
     else
-        nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
+        nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] + 1;
 
-    for(i=1; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
 }
 
 static void dct_unquantize_h263_inter_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
+    int qmul = qscale << 1;
+    int qadd = (qscale - 1) | 1;
     int nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0);
 
-    qadd = (qscale - 1) | 1;
-    qmul = qscale << 1;
-
-    nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
-
-    for(i=0; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    nCoeffs = s->inter_scantable.raster_end[s->block_last_index[n]] + 1;
+    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
 }
 
 
@@ -275,6 +250,7 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
 static av_cold int dct_init(MpegEncContext *s)
 {
     ff_blockdsp_init(&s->bdsp);
+    ff_h263dsp_init(&s->h263dsp);
     ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
     ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
 
-- 
2.45.1

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 2959 bytes --]

On Sun, Jun 09, 2024 at 07:23:45PM +0300, Rémi Denis-Courmont wrote:
> ---
>  libavcodec/mpegvideo.c | 44 ++++++++++--------------------------------
>  1 file changed, 10 insertions(+), 34 deletions(-)
> 
> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> index 7af823b8bd..9be0fecc8d 100644
> --- a/libavcodec/mpegvideo.c
> +++ b/libavcodec/mpegvideo.c
> @@ -201,13 +201,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
>  static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>                                    int16_t *block, int n, int qscale)
>  {
> -    int i, level, qmul, qadd;
> -    int nCoeffs;
> +    int qmul = qscale << 1;
> +    int qadd, nCoeffs;
>  
>      av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
>  
> -    qmul = qscale << 1;
> -
>      if (!s->h263_aic) {
>          block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
>          qadd = (qscale - 1) | 1;
> @@ -215,47 +213,24 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>          qadd = 0;
>      }
>      if(s->ac_pred)
> -        nCoeffs=63;
> +        nCoeffs = 64;
>      else
> -        nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
> +        nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] + 1;
>  
> -    for(i=1; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
>  }
>  
>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>                                    int16_t *block, int n, int qscale)
>  {
> -    int i, level, qmul, qadd;
> +    int qmul = qscale << 1;
> +    int qadd = (qscale - 1) | 1;
>      int nCoeffs;
>  
>      av_assert2(s->block_last_index[n]>=0);
>  
> -    qadd = (qscale - 1) | 1;
> -    qmul = qscale << 1;
> -
> -    nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> -
> -    for(i=0; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    nCoeffs = s->inter_scantable.raster_end[s->block_last_index[n]] + 1;
> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);

It would be better if the "+ 1" would not be needed and teh functions
would keep using "<="

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

During times of universal deceit, telling the truth becomes a
revolutionary act. -- George Orwell

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le 10 juin 2024 14:41:31 GMT+03:00, Michael Niedermayer <michael@niedermayer.cc> a écrit :
>On Sun, Jun 09, 2024 at 07:23:45PM +0300, Rémi Denis-Courmont wrote:
>> ---
>>  libavcodec/mpegvideo.c | 44 ++++++++++--------------------------------
>>  1 file changed, 10 insertions(+), 34 deletions(-)
>> 
>> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
>> index 7af823b8bd..9be0fecc8d 100644
>> --- a/libavcodec/mpegvideo.c
>> +++ b/libavcodec/mpegvideo.c
>> @@ -201,13 +201,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
>>  static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>>                                    int16_t *block, int n, int qscale)
>>  {
>> -    int i, level, qmul, qadd;
>> -    int nCoeffs;
>> +    int qmul = qscale << 1;
>> +    int qadd, nCoeffs;
>>  
>>      av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
>>  
>> -    qmul = qscale << 1;
>> -
>>      if (!s->h263_aic) {
>>          block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
>>          qadd = (qscale - 1) | 1;
>> @@ -215,47 +213,24 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>>          qadd = 0;
>>      }
>>      if(s->ac_pred)
>> -        nCoeffs=63;
>> +        nCoeffs = 64;
>>      else
>> -        nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
>> +        nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] + 1;
>>  
>> -    for(i=1; i<=nCoeffs; i++) {
>> -        level = block[i];
>> -        if (level) {
>> -            if (level < 0) {
>> -                level = level * qmul - qadd;
>> -            } else {
>> -                level = level * qmul + qadd;
>> -            }
>> -            block[i] = level;
>> -        }
>> -    }
>> +    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
>>  }
>>  
>>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>>                                    int16_t *block, int n, int qscale)
>>  {
>> -    int i, level, qmul, qadd;
>> +    int qmul = qscale << 1;
>> +    int qadd = (qscale - 1) | 1;
>>      int nCoeffs;
>>  
>>      av_assert2(s->block_last_index[n]>=0);
>>  
>> -    qadd = (qscale - 1) | 1;
>> -    qmul = qscale << 1;
>> -
>> -    nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
>> -
>> -    for(i=0; i<=nCoeffs; i++) {
>> -        level = block[i];
>> -        if (level) {
>> -            if (level < 0) {
>> -                level = level * qmul - qadd;
>> -            } else {
>> -                level = level * qmul + qadd;
>> -            }
>> -            block[i] = level;
>> -        }
>> -    }
>> +    nCoeffs = s->inter_scantable.raster_end[s->block_last_index[n]] + 1;
>> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
>
>It would be better if the "+ 1" would not be needed and teh functions
>would keep using "<="

Why? AFAICT, that just makes the assembler more confusing by requiring an unusual boundary check.

And then for SVE and RVV, adding one is unavoidable possible, as we need the element count to predicate the vector ops. So we'd just end up having to add one in the assembler instead of C.
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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 3789 bytes --]

On Mon, Jun 10, 2024 at 03:14:14PM +0300, Rémi Denis-Courmont wrote:
> 
> 
> Le 10 juin 2024 14:41:31 GMT+03:00, Michael Niedermayer <michael@niedermayer.cc> a écrit :
> >On Sun, Jun 09, 2024 at 07:23:45PM +0300, Rémi Denis-Courmont wrote:
> >> ---
> >>  libavcodec/mpegvideo.c | 44 ++++++++++--------------------------------
> >>  1 file changed, 10 insertions(+), 34 deletions(-)
> >> 
> >> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> >> index 7af823b8bd..9be0fecc8d 100644
> >> --- a/libavcodec/mpegvideo.c
> >> +++ b/libavcodec/mpegvideo.c
> >> @@ -201,13 +201,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
> >>  static void dct_unquantize_h263_intra_c(MpegEncContext *s,
> >>                                    int16_t *block, int n, int qscale)
> >>  {
> >> -    int i, level, qmul, qadd;
> >> -    int nCoeffs;
> >> +    int qmul = qscale << 1;
> >> +    int qadd, nCoeffs;
> >>  
> >>      av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
> >>  
> >> -    qmul = qscale << 1;
> >> -
> >>      if (!s->h263_aic) {
> >>          block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
> >>          qadd = (qscale - 1) | 1;
> >> @@ -215,47 +213,24 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
> >>          qadd = 0;
> >>      }
> >>      if(s->ac_pred)
> >> -        nCoeffs=63;
> >> +        nCoeffs = 64;
> >>      else
> >> -        nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
> >> +        nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] + 1;
> >>  
> >> -    for(i=1; i<=nCoeffs; i++) {
> >> -        level = block[i];
> >> -        if (level) {
> >> -            if (level < 0) {
> >> -                level = level * qmul - qadd;
> >> -            } else {
> >> -                level = level * qmul + qadd;
> >> -            }
> >> -            block[i] = level;
> >> -        }
> >> -    }
> >> +    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
> >>  }
> >>  
> >>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
> >>                                    int16_t *block, int n, int qscale)
> >>  {
> >> -    int i, level, qmul, qadd;
> >> +    int qmul = qscale << 1;
> >> +    int qadd = (qscale - 1) | 1;
> >>      int nCoeffs;
> >>  
> >>      av_assert2(s->block_last_index[n]>=0);
> >>  
> >> -    qadd = (qscale - 1) | 1;
> >> -    qmul = qscale << 1;
> >> -
> >> -    nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> >> -
> >> -    for(i=0; i<=nCoeffs; i++) {
> >> -        level = block[i];
> >> -        if (level) {
> >> -            if (level < 0) {
> >> -                level = level * qmul - qadd;
> >> -            } else {
> >> -                level = level * qmul + qadd;
> >> -            }
> >> -            block[i] = level;
> >> -        }
> >> -    }
> >> +    nCoeffs = s->inter_scantable.raster_end[s->block_last_index[n]] + 1;
> >> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
> >
> >It would be better if the "+ 1" would not be needed and teh functions
> >would keep using "<="
> 
> Why?

because its 1 instruction less and the compieler cannot optimize it out.


> AFAICT, that just makes the assembler more confusing by requiring an unusual boundary check.
> 
> And then for SVE and RVV, adding one is unavoidable possible, as we need the element count to predicate the vector ops. So we'd just end up having to add one in the assembler instead of C.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.

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[FFmpeg-devel] [PATCHv5 1/4] lavc/h263dsp: add DCT dequantisation functions

[Rémi Denis-Courmont]

Note that optimised implementations of these functions will be taken
into actual use only if MpegEncContext.dct_unquantize_h263_{inter,intra}
are *not* overloaded by existing optimisations.

---
This adds the plus ones back, saving two branch instructions in C and
one in assembler (at the cost of two unconditional adds).

---
 libavcodec/h263dsp.c | 26 ++++++++++++++++++++++++++
 libavcodec/h263dsp.h |  4 ++++
 2 files changed, 30 insertions(+)

diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
index 6a13353499..f4523a68c1 100644
--- a/libavcodec/h263dsp.c
+++ b/libavcodec/h263dsp.c
@@ -19,10 +19,34 @@
 #include <stdint.h>
 
 #include "libavutil/attributes.h"
+#include "libavutil/avassert.h"
 #include "libavutil/common.h"
 #include "config.h"
 #include "h263dsp.h"
 
+static void h263_dct_unquantize_inter_c(int16_t *block, size_t len,
+                                        int qmul, int qadd)
+{
+    for (size_t i = 0; i < len; i++) {
+        int level = block[i];
+
+        if (level) {
+            if (level < 0)
+                level = level * qmul - qadd;
+            else
+                level = level * qmul + qadd;
+            block[i] = level;
+        }
+    }
+}
+
+static void h263_dct_unquantize_intra_c(int16_t *block, size_t len,
+                                        int qmul, int qadd)
+{
+    av_assert1(len >= 1);
+    h263_dct_unquantize_inter_c(block + 1, len - 1, qmul, qadd);
+}
+
 const uint8_t ff_h263_loop_filter_strength[32] = {
     0, 1, 1, 2, 2, 3, 3,  4,  4,  4,  5,  5,  6,  6,  7, 7,
     7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12
@@ -116,6 +140,8 @@ static void h263_v_loop_filter_c(uint8_t *src, int stride, int qscale)
 
 av_cold void ff_h263dsp_init(H263DSPContext *ctx)
 {
+    ctx->h263_dct_unquantize_intra = h263_dct_unquantize_intra_c;
+    ctx->h263_dct_unquantize_inter = h263_dct_unquantize_inter_c;
     ctx->h263_h_loop_filter = h263_h_loop_filter_c;
     ctx->h263_v_loop_filter = h263_v_loop_filter_c;
 
diff --git a/libavcodec/h263dsp.h b/libavcodec/h263dsp.h
index 2dccd23392..0ecbe83314 100644
--- a/libavcodec/h263dsp.h
+++ b/libavcodec/h263dsp.h
@@ -24,6 +24,10 @@
 extern const uint8_t ff_h263_loop_filter_strength[32];
 
 typedef struct H263DSPContext {
+    void (*h263_dct_unquantize_intra)(int16_t *block /* align 16 */,
+                                      size_t len, int mul, int add);
+    void (*h263_dct_unquantize_inter)(int16_t *block /* align 16 */,
+                                      size_t len, int mul, int add);
     void (*h263_h_loop_filter)(uint8_t *src, int stride, int qscale);
     void (*h263_v_loop_filter)(uint8_t *src, int stride, int qscale);
 } H263DSPContext;
-- 
2.45.1

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[FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

---
 configure              |  4 ++--
 libavcodec/mpegvideo.c | 46 +++++++++++-------------------------------
 2 files changed, 14 insertions(+), 36 deletions(-)

diff --git a/configure b/configure
index 6baa9b0646..eb9d1b1f5d 100755
--- a/configure
+++ b/configure
@@ -2957,8 +2957,8 @@ ftr_decoder_select="adts_header"
 g2m_decoder_deps="zlib"
 g2m_decoder_select="blockdsp idctdsp jpegtables"
 g729_decoder_select="audiodsp"
-h261_decoder_select="mpegvideodec"
-h261_encoder_select="mpegvideoenc"
+h261_decoder_select="h263dsp mpegvideodec"
+h261_encoder_select="h263dsp mpegvideoenc"
 h263_decoder_select="h263_parser h263dsp mpegvideodec qpeldsp"
 h263_encoder_select="h263dsp mpegvideoenc"
 h263i_decoder_select="h263_decoder"
diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
index 7af823b8bd..b35fd37083 100644
--- a/libavcodec/mpegvideo.c
+++ b/libavcodec/mpegvideo.c
@@ -201,13 +201,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
 static void dct_unquantize_h263_intra_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
-    int nCoeffs;
+    int qmul = qscale << 1;
+    int qadd, nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
 
-    qmul = qscale << 1;
-
     if (!s->h263_aic) {
         block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
         qadd = (qscale - 1) | 1;
@@ -215,47 +213,24 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
         qadd = 0;
     }
     if(s->ac_pred)
-        nCoeffs=63;
+        nCoeffs = 64;
     else
-        nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
+        nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] + 1;
 
-    for(i=1; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
 }
 
 static void dct_unquantize_h263_inter_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
+    int qmul = qscale << 1;
+    int qadd = (qscale - 1) | 1;
     int nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0);
 
-    qadd = (qscale - 1) | 1;
-    qmul = qscale << 1;
-
-    nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
-
-    for(i=0; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    nCoeffs = s->inter_scantable.raster_end[s->block_last_index[n]] + 1;
+    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
 }
 
 
@@ -275,6 +250,9 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
 static av_cold int dct_init(MpegEncContext *s)
 {
     ff_blockdsp_init(&s->bdsp);
+#if CONFIG_H263DSP
+    ff_h263dsp_init(&s->h263dsp);
+#endif
     ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
     ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
 
-- 
2.45.1

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[James Almer]

On 6/12/2024 1:47 AM, Rémi Denis-Courmont wrote:
> ---
>   configure              |  4 ++--
>   libavcodec/mpegvideo.c | 46 +++++++++++-------------------------------
>   2 files changed, 14 insertions(+), 36 deletions(-)
> 
> diff --git a/configure b/configure
> index 6baa9b0646..eb9d1b1f5d 100755
> --- a/configure
> +++ b/configure
> @@ -2957,8 +2957,8 @@ ftr_decoder_select="adts_header"
>   g2m_decoder_deps="zlib"
>   g2m_decoder_select="blockdsp idctdsp jpegtables"
>   g729_decoder_select="audiodsp"
> -h261_decoder_select="mpegvideodec"
> -h261_encoder_select="mpegvideoenc"
> +h261_decoder_select="h263dsp mpegvideodec"
> +h261_encoder_select="h263dsp mpegvideoenc"
>   h263_decoder_select="h263_parser h263dsp mpegvideodec qpeldsp"
>   h263_encoder_select="h263dsp mpegvideoenc"
>   h263i_decoder_select="h263_decoder"
> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> index 7af823b8bd..b35fd37083 100644
> --- a/libavcodec/mpegvideo.c
> +++ b/libavcodec/mpegvideo.c
> @@ -201,13 +201,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
>   static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>                                     int16_t *block, int n, int qscale)
>   {
> -    int i, level, qmul, qadd;
> -    int nCoeffs;
> +    int qmul = qscale << 1;
> +    int qadd, nCoeffs;
>   
>       av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
>   
> -    qmul = qscale << 1;
> -
>       if (!s->h263_aic) {
>           block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
>           qadd = (qscale - 1) | 1;
> @@ -215,47 +213,24 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>           qadd = 0;
>       }
>       if(s->ac_pred)
> -        nCoeffs=63;
> +        nCoeffs = 64;
>       else
> -        nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
> +        nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] + 1;
>   
> -    for(i=1; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);

Looking further into this, you're adding a function pointer call in a 
function that's already called from a function pointer. And both x86 and 
arm have asm optimized versions of this entire method, which includes 
all the setup before the loop.

Can't you do the same for riscv? Is there anything preventing you from 
accessing fields at specific offsets within MpegEncContext?

>   }
>   
>   static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>                                     int16_t *block, int n, int qscale)
>   {
> -    int i, level, qmul, qadd;
> +    int qmul = qscale << 1;
> +    int qadd = (qscale - 1) | 1;
>       int nCoeffs;
>   
>       av_assert2(s->block_last_index[n]>=0);
>   
> -    qadd = (qscale - 1) | 1;
> -    qmul = qscale << 1;
> -
> -    nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> -
> -    for(i=0; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    nCoeffs = s->inter_scantable.raster_end[s->block_last_index[n]] + 1;
> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
>   }
>   
>   
> @@ -275,6 +250,9 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
>   static av_cold int dct_init(MpegEncContext *s)
>   {
>       ff_blockdsp_init(&s->bdsp);
> +#if CONFIG_H263DSP
> +    ff_h263dsp_init(&s->h263dsp);
> +#endif
>       ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
>       ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
>   
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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le 14 juin 2024 17:33:16 GMT+03:00, James Almer <jamrial@gmail.com> a écrit :
>On 6/12/2024 1:47 AM, Rémi Denis-Courmont wrote:
>> ---
>>   configure              |  4 ++--
>>   libavcodec/mpegvideo.c | 46 +++++++++++-------------------------------
>>   2 files changed, 14 insertions(+), 36 deletions(-)
>> 
>> diff --git a/configure b/configure
>> index 6baa9b0646..eb9d1b1f5d 100755
>> --- a/configure
>> +++ b/configure
>> @@ -2957,8 +2957,8 @@ ftr_decoder_select="adts_header"
>>   g2m_decoder_deps="zlib"
>>   g2m_decoder_select="blockdsp idctdsp jpegtables"
>>   g729_decoder_select="audiodsp"
>> -h261_decoder_select="mpegvideodec"
>> -h261_encoder_select="mpegvideoenc"
>> +h261_decoder_select="h263dsp mpegvideodec"
>> +h261_encoder_select="h263dsp mpegvideoenc"
>>   h263_decoder_select="h263_parser h263dsp mpegvideodec qpeldsp"
>>   h263_encoder_select="h263dsp mpegvideoenc"
>>   h263i_decoder_select="h263_decoder"
>> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
>> index 7af823b8bd..b35fd37083 100644
>> --- a/libavcodec/mpegvideo.c
>> +++ b/libavcodec/mpegvideo.c
>> @@ -201,13 +201,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
>>   static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>>                                     int16_t *block, int n, int qscale)
>>   {
>> -    int i, level, qmul, qadd;
>> -    int nCoeffs;
>> +    int qmul = qscale << 1;
>> +    int qadd, nCoeffs;
>>         av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
>>   -    qmul = qscale << 1;
>> -
>>       if (!s->h263_aic) {
>>           block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
>>           qadd = (qscale - 1) | 1;
>> @@ -215,47 +213,24 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>>           qadd = 0;
>>       }
>>       if(s->ac_pred)
>> -        nCoeffs=63;
>> +        nCoeffs = 64;
>>       else
>> -        nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
>> +        nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] + 1;
>>   -    for(i=1; i<=nCoeffs; i++) {
>> -        level = block[i];
>> -        if (level) {
>> -            if (level < 0) {
>> -                level = level * qmul - qadd;
>> -            } else {
>> -                level = level * qmul + qadd;
>> -            }
>> -            block[i] = level;
>> -        }
>> -    }
>> +    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
>
>Looking further into this, you're adding a function pointer call in a function that's already called from a function pointer. And both x86 and arm have asm optimized versions of this entire method, which includes all the setup before the loop.

I am not interested in copying existing bad design. Note that the Arm code uses intrinsics. I don't want to use RVV intrinsics especially just for this. And x86 only has MMX.

>Can't you do the same for riscv?

Sure, RV can address fixed offsets up to +/-2 KiB. If someone *else* adds a assembler-friendly header file that defines the offsets to the relevant context fields, and rewrites the checkasm code to match, that is.

> Is there anything preventing you from accessing fields at specific offsets within MpegEncContext?

My strong belief that that would be technically wrong, yes.
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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le perjantaina 14. kesäkuuta 2024, 17.45.50 EEST Rémi Denis-Courmont a écrit :
> And x86 only has MMX.

And the x86 code uses inline assembler. That's not viable on any ISA with sane 
conventions such as Arm or RISC-V. The compiler will reject our vector 
clobbers, unless the Vector extension is included in the compilation target. 
But then that breaks run-time detection, and will be rejected by all Linux 
distros.

-- 
Rémi Denis-Courmont
http://www.remlab.net/



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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[James Almer]

On 6/14/2024 12:11 PM, Rémi Denis-Courmont wrote:
> Le perjantaina 14. kesäkuuta 2024, 17.45.50 EEST Rémi Denis-Courmont a écrit :
>> And x86 only has MMX.
> 
> And the x86 code uses inline assembler. That's not viable on any ISA with sane
> conventions such as Arm or RISC-V. The compiler will reject our vector
> clobbers, unless the Vector extension is included in the compilation target.
> But then that breaks run-time detection, and will be rejected by all Linux
> distros.

I was thinking on removing that inline version and probably replacing it 
with sse2, using the dsp prototypes you introduce in this set.
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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le perjantaina 14. kesäkuuta 2024, 18.41.48 EEST James Almer a écrit :
> On 6/14/2024 12:11 PM, Rémi Denis-Courmont wrote:
> > Le perjantaina 14. kesäkuuta 2024, 17.45.50 EEST Rémi Denis-Courmont a 
écrit :
> >> And x86 only has MMX.
> > 
> > And the x86 code uses inline assembler. That's not viable on any ISA with
> > sane conventions such as Arm or RISC-V. The compiler will reject our
> > vector clobbers, unless the Vector extension is included in the
> > compilation target. But then that breaks run-time detection, and will be
> > rejected by all Linux distros.
> 
> I was thinking on removing that inline version and probably replacing it
> with sse2, using the dsp prototypes you introduce in this set.

I saw that, but we can't have the cake and eat it. Those DSP callbacks can't 
exist without adding a layer of indirection.

-- 
雷米‧德尼-库尔蒙
http://www.remlab.net/



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[FFmpeg-devel] [PATCH 1/4] lavc/h263dsp: add DCT dequantisation functions

[Rémi Denis-Courmont]

Note that optimised implementations of these functions will be taken
into actual use only if MpegEncContext.dct_unquantize_h263_{inter,intra}
are *not* overloaded by existing optimisations.
---
 libavcodec/h263dsp.c | 25 +++++++++++++++++++++++++
 libavcodec/h263dsp.h |  4 ++++
 2 files changed, 29 insertions(+)

diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
index 6a13353499..dc146bf821 100644
--- a/libavcodec/h263dsp.c
+++ b/libavcodec/h263dsp.c
@@ -19,10 +19,33 @@
 #include <stdint.h>
 
 #include "libavutil/attributes.h"
+#include "libavutil/avassert.h"
 #include "libavutil/common.h"
 #include "config.h"
 #include "h263dsp.h"
 
+static void h263_dct_unquantize_inter_c(int16_t *block, ptrdiff_t len,
+                                        int qmul, int qadd)
+{
+    for (ptrdiff_t i = 0; i <= len; i++) {
+        int level = block[i];
+
+        if (level) {
+            if (level < 0)
+                level = level * qmul - qadd;
+            else
+                level = level * qmul + qadd;
+            block[i] = level;
+        }
+    }
+}
+
+static void h263_dct_unquantize_intra_c(int16_t *block, ptrdiff_t len,
+                                        int qmul, int qadd)
+{
+    h263_dct_unquantize_inter_c(block + 1, len - 1, qmul, qadd);
+}
+
 const uint8_t ff_h263_loop_filter_strength[32] = {
     0, 1, 1, 2, 2, 3, 3,  4,  4,  4,  5,  5,  6,  6,  7, 7,
     7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12
@@ -116,6 +139,8 @@ static void h263_v_loop_filter_c(uint8_t *src, int stride, int qscale)
 
 av_cold void ff_h263dsp_init(H263DSPContext *ctx)
 {
+    ctx->h263_dct_unquantize_intra = h263_dct_unquantize_intra_c;
+    ctx->h263_dct_unquantize_inter = h263_dct_unquantize_inter_c;
     ctx->h263_h_loop_filter = h263_h_loop_filter_c;
     ctx->h263_v_loop_filter = h263_v_loop_filter_c;
 
diff --git a/libavcodec/h263dsp.h b/libavcodec/h263dsp.h
index 2dccd23392..d26498f491 100644
--- a/libavcodec/h263dsp.h
+++ b/libavcodec/h263dsp.h
@@ -24,6 +24,10 @@
 extern const uint8_t ff_h263_loop_filter_strength[32];
 
 typedef struct H263DSPContext {
+    void (*h263_dct_unquantize_intra)(int16_t *block /* align 16 */,
+                                      ptrdiff_t len, int mul, int add);
+    void (*h263_dct_unquantize_inter)(int16_t *block /* align 16 */,
+                                      ptrdiff_t len, int mul, int add);
     void (*h263_h_loop_filter)(uint8_t *src, int stride, int qscale);
     void (*h263_v_loop_filter)(uint8_t *src, int stride, int qscale);
 } H263DSPContext;
-- 
2.45.2

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[FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

---
 configure              |  4 ++--
 libavcodec/mpegvideo.c | 40 +++++++++-------------------------------
 2 files changed, 11 insertions(+), 33 deletions(-)

diff --git a/configure b/configure
index fed4c44cd1..42b9a72d5a 100755
--- a/configure
+++ b/configure
@@ -2954,8 +2954,8 @@ ftr_decoder_select="adts_header"
 g2m_decoder_deps="zlib"
 g2m_decoder_select="blockdsp idctdsp jpegtables"
 g729_decoder_select="audiodsp"
-h261_decoder_select="mpegvideodec"
-h261_encoder_select="mpegvideoenc"
+h261_decoder_select="h263dsp mpegvideodec"
+h261_encoder_select="h263dsp mpegvideoenc"
 h263_decoder_select="h263_parser h263dsp mpegvideodec qpeldsp"
 h263_encoder_select="h263dsp mpegvideoenc"
 h263i_decoder_select="h263_decoder"
diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
index b9a0469335..c9094d1cce 100644
--- a/libavcodec/mpegvideo.c
+++ b/libavcodec/mpegvideo.c
@@ -202,13 +202,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
 static void dct_unquantize_h263_intra_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
-    int nCoeffs;
+    int qmul = qscale << 1;
+    int qadd, nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
 
-    qmul = qscale << 1;
-
     if (!s->h263_aic) {
         block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
         qadd = (qscale - 1) | 1;
@@ -220,43 +218,20 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
     else
         nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
 
-    for(i=1; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
 }
 
 static void dct_unquantize_h263_inter_c(MpegEncContext *s,
                                   int16_t *block, int n, int qscale)
 {
-    int i, level, qmul, qadd;
+    int qmul = qscale << 1;
+    int qadd = (qscale - 1) | 1;
     int nCoeffs;
 
     av_assert2(s->block_last_index[n]>=0);
 
-    qadd = (qscale - 1) | 1;
-    qmul = qscale << 1;
-
     nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
-
-    for(i=0; i<=nCoeffs; i++) {
-        level = block[i];
-        if (level) {
-            if (level < 0) {
-                level = level * qmul - qadd;
-            } else {
-                level = level * qmul + qadd;
-            }
-            block[i] = level;
-        }
-    }
+    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
 }
 
 
@@ -276,6 +251,9 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
 static av_cold void dsp_init(MpegEncContext *s)
 {
     ff_blockdsp_init(&s->bdsp);
+#if CONFIG_H263DSP
+    ff_h263dsp_init(&s->h263dsp);
+#endif
     ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
     ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
 
-- 
2.45.2

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Andreas Rheinhardt]

Rémi Denis-Courmont:
> ---
>  configure              |  4 ++--
>  libavcodec/mpegvideo.c | 40 +++++++++-------------------------------
>  2 files changed, 11 insertions(+), 33 deletions(-)
> 
> diff --git a/configure b/configure
> index fed4c44cd1..42b9a72d5a 100755
> --- a/configure
> +++ b/configure
> @@ -2954,8 +2954,8 @@ ftr_decoder_select="adts_header"
>  g2m_decoder_deps="zlib"
>  g2m_decoder_select="blockdsp idctdsp jpegtables"
>  g729_decoder_select="audiodsp"
> -h261_decoder_select="mpegvideodec"
> -h261_encoder_select="mpegvideoenc"
> +h261_decoder_select="h263dsp mpegvideodec"

Unnecessary since f793074784ae79dabc4f83b61710161b3fe3288c
(Btw: It was not only H.261 and H.263 using these; RV34 and VC-1 did so,
too, but only for the error-resilience code. But this is no longer an
issue since 7b539ca3e6bae701d88096ff8dc3db7f13b7318a.)

> +h261_encoder_select="h263dsp mpegvideoenc"
>  h263_decoder_select="h263_parser h263dsp mpegvideodec qpeldsp"
>  h263_encoder_select="h263dsp mpegvideoenc"
>  h263i_decoder_select="h263_decoder"
> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> index b9a0469335..c9094d1cce 100644
> --- a/libavcodec/mpegvideo.c
> +++ b/libavcodec/mpegvideo.c
> @@ -202,13 +202,11 @@ static void dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
>  static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>                                    int16_t *block, int n, int qscale)
>  {
> -    int i, level, qmul, qadd;
> -    int nCoeffs;
> +    int qmul = qscale << 1;
> +    int qadd, nCoeffs;
>  
>      av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
>  
> -    qmul = qscale << 1;
> -
>      if (!s->h263_aic) {
>          block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
>          qadd = (qscale - 1) | 1;
> @@ -220,43 +218,20 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>      else
>          nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
>  
> -    for(i=1; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
>  }
>  
>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>                                    int16_t *block, int n, int qscale)
>  {
> -    int i, level, qmul, qadd;
> +    int qmul = qscale << 1;
> +    int qadd = (qscale - 1) | 1;
>      int nCoeffs;
>  
>      av_assert2(s->block_last_index[n]>=0);
>  
> -    qadd = (qscale - 1) | 1;
> -    qmul = qscale << 1;
> -
>      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> -
> -    for(i=0; i<=nCoeffs; i++) {
> -        level = block[i];
> -        if (level) {
> -            if (level < 0) {
> -                level = level * qmul - qadd;
> -            } else {
> -                level = level * qmul + qadd;
> -            }
> -            block[i] = level;
> -        }
> -    }
> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);

This adds an indirection. I have asked you to actually benchmark this
code (and not only the DSP function you add), but you never did.

>  }
>  
>  
> @@ -276,6 +251,9 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
>  static av_cold void dsp_init(MpegEncContext *s)
>  {
>      ff_blockdsp_init(&s->bdsp);
> +#if CONFIG_H263DSP
> +    ff_h263dsp_init(&s->h263dsp);
> +#endif
>      ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
>      ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
>  

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le lauantaina 6. heinäkuuta 2024, 18.23.00 EEST Andreas Rheinhardt a écrit :
> >  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
> >  
> >                                    int16_t *block, int n, int qscale)
> >  
> >  {
> > 
> > -    int i, level, qmul, qadd;
> > +    int qmul = qscale << 1;
> > +    int qadd = (qscale - 1) | 1;
> > 
> >      int nCoeffs;
> >      
> >      av_assert2(s->block_last_index[n]>=0);
> > 
> > -    qadd = (qscale - 1) | 1;
> > -    qmul = qscale << 1;
> > -
> > 
> >      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> > 
> > -
> > -    for(i=0; i<=nCoeffs; i++) {
> > -        level = block[i];
> > -        if (level) {
> > -            if (level < 0) {
> > -                level = level * qmul - qadd;
> > -            } else {
> > -                level = level * qmul + qadd;
> > -            }
> > -            block[i] = level;
> > -        }
> > -    }
> > +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
> 
> This adds an indirection. I have asked you to actually benchmark this
> code (and not only the DSP function you add), but you never did.

I already pointed out previously that this is the way this project does DSP 
code. Certainly it would be nice to hard-code the path when there is only one 
possible. This is often the case on Armv8 notably, and of course on platforms 
without optimisations.

But that's a general problem way beyond the scope of this patchset. We always 
add indirect function calls in this sort of situation, and I don't see why I 
would have duty to benchmark it, so I am going to ignore this.

-- 
雷米‧德尼-库尔蒙
http://www.remlab.net/



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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Andreas Rheinhardt]

Rémi Denis-Courmont:
> Le lauantaina 6. heinäkuuta 2024, 18.23.00 EEST Andreas Rheinhardt a écrit :
>>>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>>>  
>>>                                    int16_t *block, int n, int qscale)
>>>  
>>>  {
>>>
>>> -    int i, level, qmul, qadd;
>>> +    int qmul = qscale << 1;
>>> +    int qadd = (qscale - 1) | 1;
>>>
>>>      int nCoeffs;
>>>      
>>>      av_assert2(s->block_last_index[n]>=0);
>>>
>>> -    qadd = (qscale - 1) | 1;
>>> -    qmul = qscale << 1;
>>> -
>>>
>>>      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
>>>
>>> -
>>> -    for(i=0; i<=nCoeffs; i++) {
>>> -        level = block[i];
>>> -        if (level) {
>>> -            if (level < 0) {
>>> -                level = level * qmul - qadd;
>>> -            } else {
>>> -                level = level * qmul + qadd;
>>> -            }
>>> -            block[i] = level;
>>> -        }
>>> -    }
>>> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
>>
>> This adds an indirection. I have asked you to actually benchmark this
>> code (and not only the DSP function you add), but you never did.
> 
> I already pointed out previously that this is the way this project does DSP 
> code. Certainly it would be nice to hard-code the path when there is only one 
> possible. This is often the case on Armv8 notably, and of course on platforms 
> without optimisations.
> 
> But that's a general problem way beyond the scope of this patchset. We always 
> add indirect function calls in this sort of situation, and I don't see why I 
> would have duty to benchmark it, so I am going to ignore this.

You have a duty to benchmark it because you add it where it wasn't before.

- Andreas

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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le lauantaina 6. heinäkuuta 2024, 19.20.33 EEST Andreas Rheinhardt a écrit :
> Rémi Denis-Courmont:
> > Le lauantaina 6. heinäkuuta 2024, 18.23.00 EEST Andreas Rheinhardt a écrit 
:
> >>>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
> >>>  
> >>>                                    int16_t *block, int n, int qscale)
> >>>  
> >>>  {
> >>> 
> >>> -    int i, level, qmul, qadd;
> >>> +    int qmul = qscale << 1;
> >>> +    int qadd = (qscale - 1) | 1;
> >>> 
> >>>      int nCoeffs;
> >>>      
> >>>      av_assert2(s->block_last_index[n]>=0);
> >>> 
> >>> -    qadd = (qscale - 1) | 1;
> >>> -    qmul = qscale << 1;
> >>> -
> >>> 
> >>>      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> >>> 
> >>> -
> >>> -    for(i=0; i<=nCoeffs; i++) {
> >>> -        level = block[i];
> >>> -        if (level) {
> >>> -            if (level < 0) {
> >>> -                level = level * qmul - qadd;
> >>> -            } else {
> >>> -                level = level * qmul + qadd;
> >>> -            }
> >>> -            block[i] = level;
> >>> -        }
> >>> -    }
> >>> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
> >> 
> >> This adds an indirection. I have asked you to actually benchmark this
> >> code (and not only the DSP function you add), but you never did.
> > 
> > I already pointed out previously that this is the way this project does
> > DSP
> > code. Certainly it would be nice to hard-code the path when there is only
> > one possible. This is often the case on Armv8 notably, and of course on
> > platforms without optimisations.
> > 
> > But that's a general problem way beyond the scope of this patchset. We
> > always add indirect function calls in this sort of situation, and I don't
> > see why I would have duty to benchmark it, so I am going to ignore this.
> 
> You have a duty to benchmark it because you add it where it wasn't before.

I don't recall other people benchmarking the indirect branch they've added 
previously for other DSP code. Recent examples include VVC and FLAC. 
Rightfully so, because there is not really an alternative anyway. Even GNU 
IFUNCs and Glibc alternative libraries internally use an indirect branch 
(hidden in PLT/GOT), and FFmpeg can't self-patch at load-time like the Linux 
kernel does, nor can it generate dynamic PLT entries with direct branches.

Also if an indirect call is unacceptable, then how come the calling code is 
itself an indirect call and for abstraction rather than performance.

Your request is completely arbitrary here. Yes, there is already an indirect 
call close up, and so? I'm not trying to clean MpegEncContext here, only 
trying to add one function to checkasm, RVV and (with James' work) post-MMX 
x86.

Lastly, you don't even specify what benchmark to run. Comparing something 
against nothing is, as my manager would say, pointless, since the relative 
overhead ought to be an approximation of infinity (in practice, you end up 
measuring the overhead of the benchmarking code instead).

-- 
Rémi Denis-Courmont
http://www.remlab.net/



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Re: [FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Andreas Rheinhardt]

Rémi Denis-Courmont:
> Le lauantaina 6. heinäkuuta 2024, 19.20.33 EEST Andreas Rheinhardt a écrit :
>> Rémi Denis-Courmont:
>>> Le lauantaina 6. heinäkuuta 2024, 18.23.00 EEST Andreas Rheinhardt a écrit 
> :
>>>>>  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
>>>>>  
>>>>>                                    int16_t *block, int n, int qscale)
>>>>>  
>>>>>  {
>>>>>
>>>>> -    int i, level, qmul, qadd;
>>>>> +    int qmul = qscale << 1;
>>>>> +    int qadd = (qscale - 1) | 1;
>>>>>
>>>>>      int nCoeffs;
>>>>>      
>>>>>      av_assert2(s->block_last_index[n]>=0);
>>>>>
>>>>> -    qadd = (qscale - 1) | 1;
>>>>> -    qmul = qscale << 1;
>>>>> -
>>>>>
>>>>>      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
>>>>>
>>>>> -
>>>>> -    for(i=0; i<=nCoeffs; i++) {
>>>>> -        level = block[i];
>>>>> -        if (level) {
>>>>> -            if (level < 0) {
>>>>> -                level = level * qmul - qadd;
>>>>> -            } else {
>>>>> -                level = level * qmul + qadd;
>>>>> -            }
>>>>> -            block[i] = level;
>>>>> -        }
>>>>> -    }
>>>>> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
>>>>
>>>> This adds an indirection. I have asked you to actually benchmark this
>>>> code (and not only the DSP function you add), but you never did.
>>>
>>> I already pointed out previously that this is the way this project does
>>> DSP
>>> code. Certainly it would be nice to hard-code the path when there is only
>>> one possible. This is often the case on Armv8 notably, and of course on
>>> platforms without optimisations.
>>>
>>> But that's a general problem way beyond the scope of this patchset. We
>>> always add indirect function calls in this sort of situation, and I don't
>>> see why I would have duty to benchmark it, so I am going to ignore this.
>>
>> You have a duty to benchmark it because you add it where it wasn't before.
> 
> I don't recall other people benchmarking the indirect branch they've added 
> previously for other DSP code. Recent examples include VVC and FLAC. 
> Rightfully so, because there is not really an alternative anyway. Even GNU 
> IFUNCs and Glibc alternative libraries internally use an indirect branch 
> (hidden in PLT/GOT), and FFmpeg can't self-patch at load-time like the Linux 
> kernel does, nor can it generate dynamic PLT entries with direct branches.
> 
> Also if an indirect call is unacceptable, then how come the calling code is 
> itself an indirect call and for abstraction rather than performance.

I did not even say that it is unacceptable. Merely that it should be
benched.

> 
> Your request is completely arbitrary here. Yes, there is already an indirect 
> call close up, and so? I'm not trying to clean MpegEncContext here, only 
> trying to add one function to checkasm, RVV and (with James' work) post-MMX 
> x86.
> 
> Lastly, you don't even specify what benchmark to run. Comparing something 
> against nothing is, as my manager would say, pointless, since the relative 
> overhead ought to be an approximation of infinity (in practice, you end up 
> measuring the overhead of the benchmarking code instead).

You shall compare the function you are modifying, namely
dct_unquantize_h263_(intra|inter)_c.

- Andreas

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