ref: 7361ef732b432e153496c30da66081d7e530c7f6
dir: /vp8/decoder/dboolhuff.h/
/* * 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 VP8_DECODER_DBOOLHUFF_H_ #define 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 __cplusplus extern "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; } { register unsigned int shift = vp8_norm[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 // VP8_DECODER_DBOOLHUFF_H_