[FFmpeg-devel] [PATCH] avcodec/vc2enc: Use LUT to avoid repeated av_log2()

* [FFmpeg-devel] [PATCH] avcodec/vc2enc: Use LUT to avoid repeated av_log2()
@ 2025-05-24 11:41 Andreas Rheinhardt
  2025-05-26 14:44 ` Andreas Rheinhardt
  0 siblings, 1 reply; 2+ messages in thread
From: Andreas Rheinhardt @ 2025-05-24 11:41 UTC (permalink / raw)
  To: FFmpeg development discussions and patches

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Patch attached.

- Andreas

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From c437f573c8e703c28697a2cafd707c5bda045004 Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Sat, 24 May 2025 13:25:21 +0200
Subject: [PATCH] avcodec/vc2enc: Use LUT to avoid repeated av_log2()

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/vc2enc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/libavcodec/vc2enc.c b/libavcodec/vc2enc.c
index 99ca95c40a..b0588f6b58 100644
--- a/libavcodec/vc2enc.c
+++ b/libavcodec/vc2enc.c
@@ -193,6 +193,8 @@ static uint16_t interleaved_ue_golomb_tab[256];
 static uint16_t top_interleaved_ue_golomb_tab[256];
 /// 1 x_{k-1} ... x_0 -> 2 * k
 static uint8_t golomb_len_tab[256];
+/// quant -> av_log2(ff_dirac_qscale_tab[quant]) + 32
+static uint8_t qscale_len_tab[FF_ARRAY_ELEMS(ff_dirac_qscale_tab)];
 
 static av_cold void vc2_init_static_data(void)
 {
@@ -202,6 +204,8 @@ static av_cold void vc2_init_static_data(void)
         interleaved_ue_golomb_tab[i] = (interleaved_ue_golomb_tab[i >> 1] << 2) | (i & 1);
         top_interleaved_ue_golomb_tab[i] = interleaved_ue_golomb_tab[i] ^ (1 << golomb_len_tab[i]);
     }
+    for (size_t i = 0; i < FF_ARRAY_ELEMS(qscale_len_tab); ++i)
+        qscale_len_tab[i] = av_log2(ff_dirac_qscale_tab[i]) + 32;
 }
 
 static av_always_inline void put_vc2_ue_uint_inline(PutBitContext *pb, uint32_t val)
@@ -545,7 +549,7 @@ static void encode_subband(const VC2EncContext *s, PutBitContext *pb,
     dwtcoef *coeff = b->buf + top * b->stride;
     const uint64_t q_m = ((uint64_t)(s->qmagic_lut[quant][0])) << 2;
     const uint64_t q_a = s->qmagic_lut[quant][1];
-    const int q_s = av_log2(ff_dirac_qscale_tab[quant]) + 32;
+    const int q_s = qscale_len_tab[quant];
 
     for (y = top; y < bottom; y++) {
         for (x = left; x < right; x++) {
@@ -586,7 +590,7 @@ static int count_hq_slice(SliceArgs *slice, int quant_idx)
                 const int q_idx = quants[level][orientation];
                 const uint64_t q_m = ((uint64_t)s->qmagic_lut[q_idx][0]) << 2;
                 const uint64_t q_a = s->qmagic_lut[q_idx][1];
-                const int q_s = av_log2(ff_dirac_qscale_tab[q_idx]) + 32;
+                const int q_s = qscale_len_tab[q_idx];
 
                 const int left   = b->width  * slice->x    / s->num_x;
                 const int right  = b->width  *(slice->x+1) / s->num_x;
-- 
2.45.2


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