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#include "vp8/common/common.h" 14 15int vp8dx_start_decode(BOOL_DECODER *br, 16 const unsigned char *source, 17 unsigned int source_sz, 18 vpx_decrypt_cb decrypt_cb, 19 void *decrypt_state) 20{ 21 br->user_buffer_end = source+source_sz; 22 br->user_buffer = source; 23 br->value = 0; 24 br->count = -8; 25 br->range = 255; 26 br->decrypt_cb = decrypt_cb; 27 br->decrypt_state = decrypt_state; 28 29 if (source_sz && !source) 30 return 1; 31 32 /* Populate the buffer */ 33 vp8dx_bool_decoder_fill(br); 34 35 return 0; 36} 37 38void vp8dx_bool_decoder_fill(BOOL_DECODER *br) 39{ 40 const unsigned char *bufptr = br->user_buffer; 41 VP8_BD_VALUE value = br->value; 42 int count = br->count; 43 int shift = VP8_BD_VALUE_SIZE - CHAR_BIT - (count + CHAR_BIT); 44 size_t bytes_left = br->user_buffer_end - bufptr; 45 size_t bits_left = bytes_left * CHAR_BIT; 46 int x = (int)(shift + CHAR_BIT - bits_left); 47 int loop_end = 0; 48 unsigned char decrypted[sizeof(VP8_BD_VALUE) + 1]; 49 50 if (br->decrypt_cb) { 51 size_t n = MIN(sizeof(decrypted), bytes_left); 52 br->decrypt_cb(br->decrypt_state, bufptr, decrypted, (int)n); 53 bufptr = decrypted; 54 } 55 56 if(x >= 0) 57 { 58 count += VP8_LOTS_OF_BITS; 59 loop_end = x; 60 } 61 62 if (x < 0 || bits_left) 63 { 64 while(shift >= loop_end) 65 { 66 count += CHAR_BIT; 67 value |= (VP8_BD_VALUE)*bufptr << shift; 68 ++bufptr; 69 ++br->user_buffer; 70 shift -= CHAR_BIT; 71 } 72 } 73 74 br->value = value; 75 br->count = count; 76} 77