Coverage Report

Created: 2025-06-13 06:48

/src/libwebp/src/dec/quant_dec.c
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// Copyright 2010 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Quantizer initialization
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//
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// Author: Skal (pascal.massimino@gmail.com)
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#include "src/dec/common_dec.h"
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#include "src/dec/vp8_dec.h"
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#include "src/dec/vp8i_dec.h"
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#include "src/utils/bit_reader_utils.h"
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#include "src/webp/types.h"
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static WEBP_INLINE int clip(int v, int M) {
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  return v < 0 ? 0 : v > M ? M : v;
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}
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// Paragraph 14.1
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static const uint8_t kDcTable[128] = {
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  4,     5,   6,   7,   8,   9,  10,  10,
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  11,   12,  13,  14,  15,  16,  17,  17,
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  18,   19,  20,  20,  21,  21,  22,  22,
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  23,   23,  24,  25,  25,  26,  27,  28,
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  29,   30,  31,  32,  33,  34,  35,  36,
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  37,   37,  38,  39,  40,  41,  42,  43,
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  44,   45,  46,  46,  47,  48,  49,  50,
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  51,   52,  53,  54,  55,  56,  57,  58,
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  59,   60,  61,  62,  63,  64,  65,  66,
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  67,   68,  69,  70,  71,  72,  73,  74,
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  75,   76,  76,  77,  78,  79,  80,  81,
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  82,   83,  84,  85,  86,  87,  88,  89,
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  91,   93,  95,  96,  98, 100, 101, 102,
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  104, 106, 108, 110, 112, 114, 116, 118,
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  122, 124, 126, 128, 130, 132, 134, 136,
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  138, 140, 143, 145, 148, 151, 154, 157
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};
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static const uint16_t kAcTable[128] = {
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  4,     5,   6,   7,   8,   9,  10,  11,
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  12,   13,  14,  15,  16,  17,  18,  19,
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  20,   21,  22,  23,  24,  25,  26,  27,
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  28,   29,  30,  31,  32,  33,  34,  35,
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  36,   37,  38,  39,  40,  41,  42,  43,
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  44,   45,  46,  47,  48,  49,  50,  51,
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  52,   53,  54,  55,  56,  57,  58,  60,
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  62,   64,  66,  68,  70,  72,  74,  76,
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  78,   80,  82,  84,  86,  88,  90,  92,
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  94,   96,  98, 100, 102, 104, 106, 108,
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  110, 112, 114, 116, 119, 122, 125, 128,
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  131, 134, 137, 140, 143, 146, 149, 152,
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  155, 158, 161, 164, 167, 170, 173, 177,
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  181, 185, 189, 193, 197, 201, 205, 209,
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  213, 217, 221, 225, 229, 234, 239, 245,
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  249, 254, 259, 264, 269, 274, 279, 284
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};
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//------------------------------------------------------------------------------
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// Paragraph 9.6
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void VP8ParseQuant(VP8Decoder* const dec) {
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  VP8BitReader* const br = &dec->br;
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  const int base_q0 = VP8GetValue(br, 7, "global-header");
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  const int dqy1_dc = VP8Get(br, "global-header") ?
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       VP8GetSignedValue(br, 4, "global-header") : 0;
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  const int dqy2_dc = VP8Get(br, "global-header") ?
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       VP8GetSignedValue(br, 4, "global-header") : 0;
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  const int dqy2_ac = VP8Get(br, "global-header") ?
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       VP8GetSignedValue(br, 4, "global-header") : 0;
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  const int dquv_dc = VP8Get(br, "global-header") ?
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       VP8GetSignedValue(br, 4, "global-header") : 0;
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  const int dquv_ac = VP8Get(br, "global-header") ?
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       VP8GetSignedValue(br, 4, "global-header") : 0;
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  const VP8SegmentHeader* const hdr = &dec->segment_hdr;
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  int i;
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  for (i = 0; i < NUM_MB_SEGMENTS; ++i) {
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    int q;
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    if (hdr->use_segment) {
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      q = hdr->quantizer[i];
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      if (!hdr->absolute_delta) {
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        q += base_q0;
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      }
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    } else {
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      if (i > 0) {
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        dec->dqm[i] = dec->dqm[0];
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        continue;
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      } else {
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        q = base_q0;
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      }
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    }
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    {
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      VP8QuantMatrix* const m = &dec->dqm[i];
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      m->y1_mat[0] = kDcTable[clip(q + dqy1_dc, 127)];
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      m->y1_mat[1] = kAcTable[clip(q + 0,       127)];
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      m->y2_mat[0] = kDcTable[clip(q + dqy2_dc, 127)] * 2;
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      // For all x in [0..284], x*155/100 is bitwise equal to (x*101581) >> 16.
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      // The smallest precision for that is '(x*6349) >> 12' but 16 is a good
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      // word size.
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      m->y2_mat[1] = (kAcTable[clip(q + dqy2_ac, 127)] * 101581) >> 16;
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      if (m->y2_mat[1] < 8) m->y2_mat[1] = 8;
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      m->uv_mat[0] = kDcTable[clip(q + dquv_dc, 117)];
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      m->uv_mat[1] = kAcTable[clip(q + dquv_ac, 127)];
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      m->uv_quant = q + dquv_ac;   // for dithering strength evaluation
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    }
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  }
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}
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//------------------------------------------------------------------------------