[FFmpeg-devel] [PATCH] avcodec/vc2enc: Simplify writing dirac golomb codes

[FFmpeg-devel] [PATCH] avcodec/vc2enc: Simplify writing dirac golomb codes

[Andreas Rheinhardt]

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Patch attached.

- Andreas

[-- Attachment #2: 0001-avcodec-vc2enc-Simplify-writing-dirac-golomb-codes.patch --]
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From 4e50b2adb6de16754b629eaf18fc92d67ecdf1ca Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Sat, 8 Mar 2025 15:45:24 +0100
Subject: [PATCH] avcodec/vc2enc: Simplify writing dirac golomb codes

The earlier code used a loop to determine the number of bits used
and called ff_log2() on a power of two (and it would be easy to
keep track of the exponent of said power-of-two); neither GCC nor
Clang optimized the loop away or avoided the ff_log2().
This patch replaces the loop and the log2 with a single av_log2().

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/vc2enc.c | 30 +++---------------------------
 1 file changed, 3 insertions(+), 27 deletions(-)

diff --git a/libavcodec/vc2enc.c b/libavcodec/vc2enc.c
index b82370a753..8e68d7a89d 100644
--- a/libavcodec/vc2enc.c
+++ b/libavcodec/vc2enc.c
@@ -189,23 +189,10 @@ typedef struct VC2EncContext {
 static av_always_inline void put_vc2_ue_uint(PutBitContext *pb, uint32_t val)
 {
     int i;
-    int bits = 0;
-    unsigned topbit = 1, maxval = 1;
+    int bits = av_log2(++val);
+    unsigned topbit = 1 << bits;
     uint64_t pbits = 0;
 
-    if (!val++) {
-        put_bits(pb, 1, 1);
-        return;
-    }
-
-    while (val > maxval) {
-        topbit <<= 1;
-        maxval <<= 1;
-        maxval |=  1;
-    }
-
-    bits = ff_log2(topbit);
-
     for (i = 0; i < bits; i++) {
         topbit >>= 1;
         av_assert2(pbits <= UINT64_MAX>>3);
@@ -219,18 +206,7 @@ static av_always_inline void put_vc2_ue_uint(PutBitContext *pb, uint32_t val)
 
 static av_always_inline int count_vc2_ue_uint(uint32_t val)
 {
-    int topbit = 1, maxval = 1;
-
-    if (!val++)
-        return 1;
-
-    while (val > maxval) {
-        topbit <<= 1;
-        maxval <<= 1;
-        maxval |=  1;
-    }
-
-    return ff_log2(topbit)*2 + 1;
+    return 2 * av_log2(val + 1) + 1;
 }
 
 /* VC-2 10.4 - parse_info() */
-- 
2.45.2


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Re: [FFmpeg-devel] [PATCH] avcodec/vc2enc: Simplify writing dirac golomb codes

[Andreas Rheinhardt]

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Andreas Rheinhardt:
> Patch attached.
> 
> - Andreas
> 

Another patch attached

- Andreas

[-- Attachment #2: 0002-avcodec-put_bits-Add-and-use-put_bits63.patch --]
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From 37d77b0820c19ea5519769d13a3e54ba88234c0e Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Sat, 8 Mar 2025 17:35:32 +0100
Subject: [PATCH 2/2] avcodec/put_bits: Add and use put_bits63()

When using a 64bit PutBitContext (i.e. on x64), put_bits_no_assert()
can naturally write up to 63 bits. So one can avoid treating the
cases <32bits, 32 bits and <63 bits differently.

As it turns out, no user actually wants to write 64 bit at once
(maybe except testprograms).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/dovi_rpuenc.c  |  8 ++++----
 libavcodec/put_bits.h     | 29 ++++++++++++++++++++++-------
 libavcodec/put_golomb.h   |  2 +-
 libavcodec/vc2enc.c       |  2 +-
 libavformat/iamf_parse.c  |  2 +-
 libavformat/iamf_writer.c |  2 +-
 6 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/libavcodec/dovi_rpuenc.c b/libavcodec/dovi_rpuenc.c
index eb79a3af5d..334b2c98a0 100644
--- a/libavcodec/dovi_rpuenc.c
+++ b/libavcodec/dovi_rpuenc.c
@@ -334,12 +334,12 @@ static inline void put_ue_coef(PutBitContext *pb, const AVDOVIRpuDataHeader *hdr
     switch (hdr->coef_data_type) {
     case RPU_COEFF_FIXED:
         set_ue_golomb(pb, coef >> hdr->coef_log2_denom);
-        put_bits64(pb, hdr->coef_log2_denom,
+        put_bits63(pb, hdr->coef_log2_denom,
                    coef & ((1LL << hdr->coef_log2_denom) - 1));
         break;
     case RPU_COEFF_FLOAT:
         fpart.f32 = coef / (float) (1LL << hdr->coef_log2_denom);
-        put_bits64(pb, hdr->coef_log2_denom, fpart.u32);
+        put_bits63(pb, hdr->coef_log2_denom, fpart.u32);
         break;
     }
 }
@@ -352,12 +352,12 @@ static inline void put_se_coef(PutBitContext *pb, const AVDOVIRpuDataHeader *hdr
     switch (hdr->coef_data_type) {
     case RPU_COEFF_FIXED:
         set_se_golomb(pb, coef >> hdr->coef_log2_denom);
-        put_bits64(pb, hdr->coef_log2_denom,
+        put_bits63(pb, hdr->coef_log2_denom,
                    coef & ((1LL << hdr->coef_log2_denom) - 1));
         break;
     case RPU_COEFF_FLOAT:
         fpart.f32 = coef / (float) (1LL << hdr->coef_log2_denom);
-        put_bits64(pb, hdr->coef_log2_denom, fpart.u32);
+        put_bits63(pb, hdr->coef_log2_denom, fpart.u32);
         break;
     }
 }
diff --git a/libavcodec/put_bits.h b/libavcodec/put_bits.h
index 0caaa6b338..56c3f4cc6d 100644
--- a/libavcodec/put_bits.h
+++ b/libavcodec/put_bits.h
@@ -39,14 +39,14 @@
 typedef uint64_t BitBuf;
 #define AV_WBBUF AV_WB64
 #define AV_WLBUF AV_WL64
+#define BUF_BITS 64
 #else
 typedef uint32_t BitBuf;
 #define AV_WBBUF AV_WB32
 #define AV_WLBUF AV_WL32
+#define BUF_BITS 32
 #endif
 
-static const int BUF_BITS = 8 * sizeof(BitBuf);
-
 typedef struct PutBitContext {
     BitBuf bit_buf;
     int bit_left;
@@ -329,12 +329,15 @@ static void av_unused put_bits32(PutBitContext *s, uint32_t value)
 }
 
 /**
- * Write up to 64 bits into a bitstream.
+ * Write up to 63 bits into a bitstream.
  */
-static inline void put_bits64(PutBitContext *s, int n, uint64_t value)
+static inline void put_bits63(PutBitContext *s, int n, uint64_t value)
 {
-    av_assert2((n == 64) || (n < 64 && value < (UINT64_C(1) << n)));
+    av_assert2(n < 64U && value < (UINT64_C(1) << n));
 
+#if BUF_BITS >= 64
+    put_bits_no_assert(s, n, value);
+#else
     if (n < 32)
         put_bits(s, n, value);
     else if (n == 32)
@@ -349,6 +352,19 @@ static inline void put_bits64(PutBitContext *s, int n, uint64_t value)
         put_bits(s, n - 32, hi);
         put_bits32(s, lo);
 #endif
+    }
+#endif
+}
+
+/**
+ * Write up to 64 bits into a bitstream.
+ */
+static inline void put_bits64(PutBitContext *s, int n, uint64_t value)
+{
+    av_assert2((n == 64) || (n < 64 && value < (UINT64_C(1) << n)));
+
+    if (n < 64) {
+        put_bits63(s, n, value);
     } else {
         uint32_t lo = value & 0xffffffff;
         uint32_t hi = value >> 32;
@@ -359,7 +375,6 @@ static inline void put_bits64(PutBitContext *s, int n, uint64_t value)
         put_bits32(s, hi);
         put_bits32(s, lo);
 #endif
-
     }
 }
 
@@ -367,7 +382,7 @@ static inline void put_sbits63(PutBitContext *pb, int n, int64_t value)
 {
     av_assert2(n >= 0 && n < 64);
 
-    put_bits64(pb, n, (uint64_t)(value) & (~(UINT64_MAX << n)));
+    put_bits63(pb, n, (uint64_t)(value) & (~(UINT64_MAX << n)));
 }
 
 /**
diff --git a/libavcodec/put_golomb.h b/libavcodec/put_golomb.h
index 43c1233fdb..91e7852a17 100644
--- a/libavcodec/put_golomb.h
+++ b/libavcodec/put_golomb.h
@@ -62,7 +62,7 @@ static inline void set_ue_golomb_long(PutBitContext *pb, uint32_t i)
         put_bits(pb, ff_ue_golomb_len[i], i + 1);
     else {
         int e = av_log2(i + 1);
-        put_bits64(pb, 2 * e + 1, i + 1);
+        put_bits63(pb, 2 * e + 1, i + 1);
     }
 }
 
diff --git a/libavcodec/vc2enc.c b/libavcodec/vc2enc.c
index 8e68d7a89d..20022f2205 100644
--- a/libavcodec/vc2enc.c
+++ b/libavcodec/vc2enc.c
@@ -201,7 +201,7 @@ static av_always_inline void put_vc2_ue_uint(PutBitContext *pb, uint32_t val)
             pbits |= 0x1;
     }
 
-    put_bits64(pb, bits*2 + 1, (pbits << 1) | 1);
+    put_bits63(pb, 2 * bits + 1, (pbits << 1) | 1);
 }
 
 static av_always_inline int count_vc2_ue_uint(uint32_t val)
diff --git a/libavformat/iamf_parse.c b/libavformat/iamf_parse.c
index db40ae37ab..abedfdb066 100644
--- a/libavformat/iamf_parse.c
+++ b/libavformat/iamf_parse.c
@@ -319,7 +319,7 @@ static int update_extradata(AVCodecParameters *codecpar)
             return ret;
 
         put_bits32(&pb, get_bits_long(&gb, 32)); // min/max blocksize
-        put_bits64(&pb, 48, get_bits64(&gb, 48)); // min/max framesize
+        put_bits63(&pb, 48, get_bits64(&gb, 48)); // min/max framesize
         put_bits(&pb, 20, get_bits(&gb, 20)); // samplerate
         skip_bits(&gb, 3);
         put_bits(&pb, 3, codecpar->ch_layout.nb_channels - 1);
diff --git a/libavformat/iamf_writer.c b/libavformat/iamf_writer.c
index 6b07dd85c9..acac6b87eb 100644
--- a/libavformat/iamf_writer.c
+++ b/libavformat/iamf_writer.c
@@ -59,7 +59,7 @@ static int update_extradata(IAMFCodecConfig *codec_config)
             return ret;
 
         put_bits32(&pb, get_bits_long(&gb, 32)); // min/max blocksize
-        put_bits64(&pb, 48, get_bits64(&gb, 48)); // min/max framesize
+        put_bits63(&pb, 48, get_bits64(&gb, 48)); // min/max framesize
         put_bits(&pb, 20, get_bits(&gb, 20)); // samplerate
         skip_bits(&gb, 3);
         put_bits(&pb, 3, 1); // set channels to stereo
-- 
2.45.2


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