vpx_dsp/bitwriter.h

   1 /*
   2  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
   3  *
   4  *  Use of this source code is governed by a BSD-style license
   5  *  that can be found in the LICENSE file in the root of the source
   6  *  tree. An additional intellectual property rights grant can be found
   7  *  in the file PATENTS.  All contributing project authors may
   8  *  be found in the AUTHORS file in the root of the source tree.
   9  */
  10
  11 #ifndef VPX_DSP_BITWRITER_H_
  12 #define VPX_DSP_BITWRITER_H_
  13
  14 #include "vpx_ports/mem.h"
  15
  16 #include "vpx_dsp/prob.h"
  17
  18 #ifdef __cplusplus
  19 extern "C" {
  20 #endif
  21
  22 typedef struct vpx_writer {
  23   unsigned int lowvalue;
  24   unsigned int range;
  25   int count;
  26   unsigned int pos;
  27   uint8_t *buffer;
  28 } vpx_writer;
  29
  30 void vpx_start_encode(vpx_writer *bc, uint8_t *buffer);
  31 void vpx_stop_encode(vpx_writer *bc);
  32
  33 static INLINE void vpx_write(vpx_writer *br, int bit, int probability) {
  34   unsigned int split;
  35   int count = br->count;
  36   unsigned int range = br->range;
  37   unsigned int lowvalue = br->lowvalue;
  38   register int shift;
  39
  40   split = 1 + (((range - 1) * probability) >> 8);
  41
  42   range = split;
  43
  44   if (bit) {
  45     lowvalue += split;
  46     range = br->range - split;
  47   }
  48
  49   shift = vpx_norm[range];
  50
  51   range <<= shift;
  52   count += shift;
  53
  54   if (count >= 0) {
  55     int offset = shift - count;
  56
  57     if ((lowvalue << (offset - 1)) & 0x80000000) {
  58       int x = br->pos - 1;
  59
  60       while (x >= 0 && br->buffer[x] == 0xff) {
  61         br->buffer[x] = 0;
  62         x--;
  63       }
  64
  65       br->buffer[x] += 1;
  66     }
  67
  68     br->buffer[br->pos++] = (lowvalue >> (24 - offset));
  69     lowvalue <<= offset;
  70     shift = count;
  71     lowvalue &= 0xffffff;
  72     count -= 8;
  73   }
  74
  75   lowvalue <<= shift;
  76   br->count = count;
  77   br->lowvalue = lowvalue;
  78   br->range = range;
  79 }
  80
  81 static INLINE void vpx_write_bit(vpx_writer *w, int bit) {
  82   vpx_write(w, bit, 128);  // vpx_prob_half
  83 }
  84
  85 static INLINE void vpx_write_literal(vpx_writer *w, int data, int bits) {
  86   int bit;
  87
  88   for (bit = bits - 1; bit >= 0; bit--)
  89     vpx_write_bit(w, 1 & (data >> bit));
  90 }
  91
  92 #define vpx_write_prob(w, v) vpx_write_literal((w), (v), 8)
  93
  94 #ifdef __cplusplus
  95 }  // extern "C"
  96 #endif
  97
  98 #endif  // VPX_DSP_BITWRITER_H_