/* *  Copyright (c) 2010 The WebM project authors. All Rights Reserved. * *  Use of this source code is governed by a BSD-style license *  that can be found in the LICENSE file in the root of the source *  tree. An additional intellectual property rights grant can be found *  in the file PATENTS.  All contributing project authors may *  be found in the AUTHORS file in the root of the source tree. */ #ifndef VPX_VP8_DECODER_DBOOLHUFF_H_#define VPX_VP8_DECODER_DBOOLHUFF_H_ #include <stddef.h>#include <limits.h> #include "./vpx_config.h"#include "vpx_ports/mem.h"#include "vpx/vp8dx.h"#include "vpx/vpx_integer.h" #ifdef __cplusplusextern "C" {#endif typedef size_t VP8_BD_VALUE; #define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE) * CHAR_BIT) /*This is meant to be a large, positive constant that can still be efficiently   loaded as an immediate (on platforms like ARM, for example).  Even relatively modest values like 100 would work fine.*/#define VP8_LOTS_OF_BITS (0x40000000) typedef struct {  const unsigned char *user_buffer_end;  const unsigned char *user_buffer;  VP8_BD_VALUE value;  int count;  unsigned int range;  vpx_decrypt_cb decrypt_cb;  void *decrypt_state;} BOOL_DECODER; DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]); int vp8dx_start_decode(BOOL_DECODER *br, const unsigned char *source,                       unsigned int source_sz, vpx_decrypt_cb decrypt_cb,                       void *decrypt_state); void vp8dx_bool_decoder_fill(BOOL_DECODER *br); static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {  unsigned int bit = 0;  VP8_BD_VALUE value;  unsigned int split;  VP8_BD_VALUE bigsplit;  int count;  unsigned int range;   split = 1 + (((br->range - 1) * probability) >> 8);   if (br->count < 0) vp8dx_bool_decoder_fill(br);   value = br->value;  count = br->count;   bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);   range = split;   if (value >= bigsplit) {    range = br->range - split;    value = value - bigsplit;    bit = 1;  }   {    const unsigned char shift = vp8_norm[(unsigned char)range];    range <<= shift;    value <<= shift;    count -= shift;  }  br->value = value;  br->count = count;  br->range = range;   return bit;} static INLINE int vp8_decode_value(BOOL_DECODER *br, int bits) {  int z = 0;  int bit;   for (bit = bits - 1; bit >= 0; bit--) {    z |= (vp8dx_decode_bool(br, 0x80) << bit);  }   return z;} static INLINE int vp8dx_bool_error(BOOL_DECODER *br) {  /* Check if we have reached the end of the buffer.   *   * Variable 'count' stores the number of bits in the 'value' buffer, minus   * 8. The top byte is part of the algorithm, and the remainder is buffered   * to be shifted into it. So if count == 8, the top 16 bits of 'value' are   * occupied, 8 for the algorithm and 8 in the buffer.   *   * When reading a byte from the user's buffer, count is filled with 8 and   * one byte is filled into the value buffer. When we reach the end of the   * data, count is additionally filled with VP8_LOTS_OF_BITS. So when   * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.   */  if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS)) {    /* We have tried to decode bits after the end of     * stream was encountered.     */    return 1;  }   /* No error. */  return 0;} #ifdef __cplusplus}  // extern "C"#endif #endif  // VPX_VP8_DECODER_DBOOLHUFF_H_