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      1 // Copyright 2010 Google Inc. All Rights Reserved.
      2 //
      3 // Use of this source code is governed by a BSD-style license
      4 // that can be found in the COPYING file in the root of the source
      5 // tree. An additional intellectual property rights grant can be found
      6 // in the file PATENTS. All contributing project authors may
      7 // be found in the AUTHORS file in the root of the source tree.
      8 // -----------------------------------------------------------------------------
      9 //
     10 // Quantizer initialization
     11 //
     12 // Author: Skal (pascal.massimino (at) gmail.com)
     13 
     14 #include "./vp8i.h"
     15 
     16 static WEBP_INLINE int clip(int v, int M) {
     17   return v < 0 ? 0 : v > M ? M : v;
     18 }
     19 
     20 // Paragraph 14.1
     21 static const uint8_t kDcTable[128] = {
     22   4,     5,   6,   7,   8,   9,  10,  10,
     23   11,   12,  13,  14,  15,  16,  17,  17,
     24   18,   19,  20,  20,  21,  21,  22,  22,
     25   23,   23,  24,  25,  25,  26,  27,  28,
     26   29,   30,  31,  32,  33,  34,  35,  36,
     27   37,   37,  38,  39,  40,  41,  42,  43,
     28   44,   45,  46,  46,  47,  48,  49,  50,
     29   51,   52,  53,  54,  55,  56,  57,  58,
     30   59,   60,  61,  62,  63,  64,  65,  66,
     31   67,   68,  69,  70,  71,  72,  73,  74,
     32   75,   76,  76,  77,  78,  79,  80,  81,
     33   82,   83,  84,  85,  86,  87,  88,  89,
     34   91,   93,  95,  96,  98, 100, 101, 102,
     35   104, 106, 108, 110, 112, 114, 116, 118,
     36   122, 124, 126, 128, 130, 132, 134, 136,
     37   138, 140, 143, 145, 148, 151, 154, 157
     38 };
     39 
     40 static const uint16_t kAcTable[128] = {
     41   4,     5,   6,   7,   8,   9,  10,  11,
     42   12,   13,  14,  15,  16,  17,  18,  19,
     43   20,   21,  22,  23,  24,  25,  26,  27,
     44   28,   29,  30,  31,  32,  33,  34,  35,
     45   36,   37,  38,  39,  40,  41,  42,  43,
     46   44,   45,  46,  47,  48,  49,  50,  51,
     47   52,   53,  54,  55,  56,  57,  58,  60,
     48   62,   64,  66,  68,  70,  72,  74,  76,
     49   78,   80,  82,  84,  86,  88,  90,  92,
     50   94,   96,  98, 100, 102, 104, 106, 108,
     51   110, 112, 114, 116, 119, 122, 125, 128,
     52   131, 134, 137, 140, 143, 146, 149, 152,
     53   155, 158, 161, 164, 167, 170, 173, 177,
     54   181, 185, 189, 193, 197, 201, 205, 209,
     55   213, 217, 221, 225, 229, 234, 239, 245,
     56   249, 254, 259, 264, 269, 274, 279, 284
     57 };
     58 
     59 //------------------------------------------------------------------------------
     60 // Paragraph 9.6
     61 
     62 void VP8ParseQuant(VP8Decoder* const dec) {
     63   VP8BitReader* const br = &dec->br_;
     64   const int base_q0 = VP8GetValue(br, 7);
     65   const int dqy1_dc = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
     66   const int dqy2_dc = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
     67   const int dqy2_ac = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
     68   const int dquv_dc = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
     69   const int dquv_ac = VP8Get(br) ? VP8GetSignedValue(br, 4) : 0;
     70 
     71   const VP8SegmentHeader* const hdr = &dec->segment_hdr_;
     72   int i;
     73 
     74   for (i = 0; i < NUM_MB_SEGMENTS; ++i) {
     75     int q;
     76     if (hdr->use_segment_) {
     77       q = hdr->quantizer_[i];
     78       if (!hdr->absolute_delta_) {
     79         q += base_q0;
     80       }
     81     } else {
     82       if (i > 0) {
     83         dec->dqm_[i] = dec->dqm_[0];
     84         continue;
     85       } else {
     86         q = base_q0;
     87       }
     88     }
     89     {
     90       VP8QuantMatrix* const m = &dec->dqm_[i];
     91       m->y1_mat_[0] = kDcTable[clip(q + dqy1_dc, 127)];
     92       m->y1_mat_[1] = kAcTable[clip(q + 0,       127)];
     93 
     94       m->y2_mat_[0] = kDcTable[clip(q + dqy2_dc, 127)] * 2;
     95       // For all x in [0..284], x*155/100 is bitwise equal to (x*101581) >> 16.
     96       // The smallest precision for that is '(x*6349) >> 12' but 16 is a good
     97       // word size.
     98       m->y2_mat_[1] = (kAcTable[clip(q + dqy2_ac, 127)] * 101581) >> 16;
     99       if (m->y2_mat_[1] < 8) m->y2_mat_[1] = 8;
    100 
    101       m->uv_mat_[0] = kDcTable[clip(q + dquv_dc, 117)];
    102       m->uv_mat_[1] = kAcTable[clip(q + dquv_ac, 127)];
    103 
    104       m->uv_quant_ = q + dquv_ac;   // for dithering strength evaluation
    105     }
    106   }
    107 }
    108 
    109 //------------------------------------------------------------------------------
    110 
    111