/* * 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 dboolhuff.LICENSE file in this directory. * See the libvpx original distribution for more information, * including patent information, and author information. */ #ifndef DBOOLHUFF_H #define DBOOLHUFF_H #include <stddef.h> #include <limits.h> #include <glib.h> 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; } BOOL_DECODER; #ifdef _MSC_VER __declspec(align(16)) extern const unsigned char vp8_norm[256]; #else extern const unsigned char vp8_norm[256] __attribute__((aligned(16))); #endif int vp8dx_start_decode(BOOL_DECODER *br, const unsigned char *source, unsigned int source_sz); void vp8dx_bool_decoder_fill(BOOL_DECODER *br); /*The refill loop is used in several places, so define it in a macro to make sure they're all consistent. An inline function would be cleaner, but has a significant penalty, because multiple BOOL_DECODER fields must be modified, and the compiler is not smart enough to eliminate the stores to those fields and the subsequent reloads from them when inlining the function.*/ #define VP8DX_BOOL_DECODER_FILL(_count,_value,_bufptr,_bufend) \ do \ { \ int shift = VP8_BD_VALUE_SIZE - 8 - ((_count) + 8); \ int loop_end, x; \ size_t bits_left = ((_bufend)-(_bufptr))*CHAR_BIT; \ \ x = shift + CHAR_BIT - bits_left; \ loop_end = 0; \ if(x >= 0) \ { \ (_count) += VP8_LOTS_OF_BITS; \ loop_end = x; \ if(!bits_left) break; \ } \ while(shift >= loop_end) \ { \ (_count) += CHAR_BIT; \ (_value) |= (VP8_BD_VALUE)*(_bufptr)++ << shift; \ shift -= CHAR_BIT; \ } \ } \ while(0) \ 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 G_GNUC_UNUSED 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 G_GNUC_UNUSED 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; } #endif