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 12 #include "dboolhuff.h" 13 14 int vp8dx_start_decode(BOOL_DECODER *br, 15 const unsigned char *source, 16 unsigned int source_sz, 17 vp8_decrypt_cb *decrypt_cb, 18 void *decrypt_state) 19 { 20 br->user_buffer_end = source+source_sz; 21 br->user_buffer = source; 22 br->value = 0; 23 br->count = -8; 24 br->range = 255; 25 br->decrypt_cb = decrypt_cb; 26 br->decrypt_state = decrypt_state; 27 28 if (source_sz && !source) 29 return 1; 30 31 /* Populate the buffer */ 32 vp8dx_bool_decoder_fill(br); 33 34 return 0; 35 } 36 37 void vp8dx_bool_decoder_fill(BOOL_DECODER *br) 38 { 39 const unsigned char *bufptr = br->user_buffer; 40 VP8_BD_VALUE value = br->value; 41 int count = br->count; 42 int shift = VP8_BD_VALUE_SIZE - 8 - (count + 8); 43 size_t bytes_left = br->user_buffer_end - bufptr; 44 size_t bits_left = bytes_left * CHAR_BIT; 45 int x = (int)(shift + CHAR_BIT - bits_left); 46 int loop_end = 0; 47 unsigned char decrypted[sizeof(VP8_BD_VALUE) + 1]; 48 49 if (br->decrypt_cb) { 50 size_t n = bytes_left > sizeof(decrypted) ? sizeof(decrypted) : bytes_left; 51 br->decrypt_cb(br->decrypt_state, bufptr, decrypted, (int)n); 52 bufptr = decrypted; 53 } 54 55 if(x >= 0) 56 { 57 count += VP8_LOTS_OF_BITS; 58 loop_end = x; 59 } 60 61 if (x < 0 || bits_left) 62 { 63 while(shift >= loop_end) 64 { 65 count += CHAR_BIT; 66 value |= (VP8_BD_VALUE)*bufptr << shift; 67 ++bufptr; 68 ++br->user_buffer; 69 shift -= CHAR_BIT; 70 } 71 } 72 73 br->value = value; 74 br->count = count; 75 } 76
