ref: a736bf6bfb66d08848b114344731c4e04ac5066d
dir: /vpx_dsp/bitreader.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 VPX_DSP_BITREADER_H_ #define VPX_DSP_BITREADER_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" #include "vpx_dsp/prob.h" #ifdef __cplusplus extern "C" { #endif typedef size_t BD_VALUE; #define BD_VALUE_SIZE ((int)sizeof(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 LOTS_OF_BITS 0x40000000 typedef struct { // Be careful when reordering this struct, it may impact the cache negatively. BD_VALUE value; unsigned int range; int count; const uint8_t *buffer_end; const uint8_t *buffer; vpx_decrypt_cb decrypt_cb; void *decrypt_state; uint8_t clear_buffer[sizeof(BD_VALUE) + 1]; } vpx_reader; int vpx_reader_init(vpx_reader *r, const uint8_t *buffer, size_t size, vpx_decrypt_cb decrypt_cb, void *decrypt_state); void vpx_reader_fill(vpx_reader *r); const uint8_t *vpx_reader_find_end(vpx_reader *r); static INLINE int vpx_reader_has_error(vpx_reader *r) { // 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 LOTS_OF_BITS. So when // count == LOTS_OF_BITS - 1, the user's data has been exhausted. // // 1 if we have tried to decode bits after the end of stream was encountered. // 0 No error. return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS; } static INLINE int vpx_read(vpx_reader *r, int prob) { unsigned int bit = 0; BD_VALUE value; BD_VALUE bigsplit; int count; unsigned int range; unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT; if (r->count < 0) vpx_reader_fill(r); value = r->value; count = r->count; bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT); range = split; if (value >= bigsplit) { range = r->range - split; value = value - bigsplit; bit = 1; } { register unsigned int shift = vpx_norm[range]; range <<= shift; value <<= shift; count -= shift; } r->value = value; r->count = count; r->range = range; return bit; } static INLINE int vpx_read_bit(vpx_reader *r) { return vpx_read(r, 128); // vpx_prob_half } static INLINE int vpx_read_literal(vpx_reader *r, int bits) { int literal = 0, bit; for (bit = bits - 1; bit >= 0; bit--) literal |= vpx_read_bit(r) << bit; return literal; } static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree, const vpx_prob *probs) { vpx_tree_index i = 0; while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0) continue; return -i; } #ifdef __cplusplus } // extern "C" #endif #endif // VPX_DSP_BITREADER_H_