vpx_dsp/bitreader.c

   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 #include <stdlib.h>
  11
  12 #include "./vpx_config.h"
  13
  14 #include "vpx_dsp/bitreader.h"
  15 #include "vpx_dsp/prob.h"
  16 #include "vpx_dsp/vpx_dsp_common.h"
  17 #include "vpx_ports/mem.h"
  18 #include "vpx_mem/vpx_mem.h"
  19 #include "vpx_util/endian_inl.h"
  20
  21 int vpx_reader_init(vpx_reader *r,
  22                     const uint8_t *buffer,
  23                     size_t size,
  24                     vpx_decrypt_cb decrypt_cb,
  25                     void *decrypt_state) {
  26   if (size && !buffer) {
  27     return 1;
  28   } else {
  29     r->buffer_end = buffer + size;
  30     r->buffer = buffer;
  31     r->value = 0;
  32     r->count = -8;
  33     r->range = 255;
  34     r->decrypt_cb = decrypt_cb;
  35     r->decrypt_state = decrypt_state;
  36     vpx_reader_fill(r);
  37     return vpx_read_bit(r) != 0;  // marker bit
  38   }
  39 }
  40
  41 void vpx_reader_fill(vpx_reader *r) {
  42   const uint8_t *const buffer_end = r->buffer_end;
  43   const uint8_t *buffer = r->buffer;
  44   const uint8_t *buffer_start = buffer;
  45   BD_VALUE value = r->value;
  46   int count = r->count;
  47   const size_t bytes_left = buffer_end - buffer;
  48   const size_t bits_left = bytes_left * CHAR_BIT;
  49   int shift = BD_VALUE_SIZE - CHAR_BIT - (count + CHAR_BIT);
  50
  51   if (r->decrypt_cb) {
  52     size_t n = VPXMIN(sizeof(r->clear_buffer), bytes_left);
  53     r->decrypt_cb(r->decrypt_state, buffer, r->clear_buffer, (int)n);
  54     buffer = r->clear_buffer;
  55     buffer_start = r->clear_buffer;
  56   }
  57   if (bits_left > BD_VALUE_SIZE) {
  58       const int bits = (shift & 0xfffffff8) + CHAR_BIT;
  59       BD_VALUE nv;
  60       BD_VALUE big_endian_values;
  61       memcpy(&big_endian_values, buffer, sizeof(BD_VALUE));
  62 #if SIZE_MAX == 0xffffffffffffffffULL
  63         big_endian_values = HToBE64(big_endian_values);
  64 #else
  65         big_endian_values = HToBE32(big_endian_values);
  66 #endif
  67       nv = big_endian_values >> (BD_VALUE_SIZE - bits);
  68       count += bits;
  69       buffer += (bits >> 3);
  70       value = r->value | (nv << (shift & 0x7));
  71   } else {
  72     const int bits_over = (int)(shift + CHAR_BIT - bits_left);
  73     int loop_end = 0;
  74     if (bits_over >= 0) {
  75       count += LOTS_OF_BITS;
  76       loop_end = bits_over;
  77     }
  78
  79     if (bits_over < 0 || bits_left) {
  80       while (shift >= loop_end) {
  81         count += CHAR_BIT;
  82         value |= (BD_VALUE)*buffer++ << shift;
  83         shift -= CHAR_BIT;
  84       }
  85     }
  86   }
  87
  88   // NOTE: Variable 'buffer' may not relate to 'r->buffer' after decryption,
  89   // so we increase 'r->buffer' by the amount that 'buffer' moved, rather than
  90   // assign 'buffer' to 'r->buffer'.
  91   r->buffer += buffer - buffer_start;
  92   r->value = value;
  93   r->count = count;
  94 }
  95
  96 const uint8_t *vpx_reader_find_end(vpx_reader *r) {
  97   // Find the end of the coded buffer
  98   while (r->count > CHAR_BIT && r->count < BD_VALUE_SIZE) {
  99     r->count -= CHAR_BIT;
 100     r->buffer--;
 101   }
 102   return r->buffer;
 103 }