michael@0: /*
michael@0:  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
michael@0:  *
michael@0:  *  Use of this source code is governed by a BSD-style license
michael@0:  *  that can be found in the LICENSE file in the root of the source
michael@0:  *  tree. An additional intellectual property rights grant can be found
michael@0:  *  in the file PATENTS.  All contributing project authors may
michael@0:  *  be found in the AUTHORS file in the root of the source tree.
michael@0:  */
michael@0: 
michael@0: 
michael@0: #ifndef DBOOLHUFF_H_
michael@0: #define DBOOLHUFF_H_
michael@0: 
michael@0: #include <stddef.h>
michael@0: #include <limits.h>
michael@0: 
michael@0: #include "vpx_config.h"
michael@0: #include "vpx_ports/mem.h"
michael@0: #include "vpx/vpx_integer.h"
michael@0: 
michael@0: typedef size_t VP8_BD_VALUE;
michael@0: 
michael@0: #define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE)*CHAR_BIT)
michael@0: 
michael@0: /*This is meant to be a large, positive constant that can still be efficiently
michael@0:    loaded as an immediate (on platforms like ARM, for example).
michael@0:   Even relatively modest values like 100 would work fine.*/
michael@0: #define VP8_LOTS_OF_BITS (0x40000000)
michael@0: 
michael@0: /*Decrypt n bytes of data from input -> output, using the decrypt_state
michael@0:    passed in VP8D_SET_DECRYPTOR.
michael@0: */
michael@0: typedef void (vp8_decrypt_cb)(void *decrypt_state, const unsigned char *input,
michael@0:                               unsigned char *output, int count);
michael@0: 
michael@0: typedef struct
michael@0: {
michael@0:     const unsigned char *user_buffer_end;
michael@0:     const unsigned char *user_buffer;
michael@0:     VP8_BD_VALUE         value;
michael@0:     int                  count;
michael@0:     unsigned int         range;
michael@0:     vp8_decrypt_cb      *decrypt_cb;
michael@0:     void                *decrypt_state;
michael@0: } BOOL_DECODER;
michael@0: 
michael@0: DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);
michael@0: 
michael@0: int vp8dx_start_decode(BOOL_DECODER *br,
michael@0:                        const unsigned char *source,
michael@0:                        unsigned int source_sz,
michael@0:                        vp8_decrypt_cb *decrypt_cb,
michael@0:                        void *decrypt_state);
michael@0: 
michael@0: void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
michael@0: 
michael@0: 
michael@0: static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
michael@0:     unsigned int bit = 0;
michael@0:     VP8_BD_VALUE value;
michael@0:     unsigned int split;
michael@0:     VP8_BD_VALUE bigsplit;
michael@0:     int count;
michael@0:     unsigned int range;
michael@0: 
michael@0:     split = 1 + (((br->range - 1) * probability) >> 8);
michael@0: 
michael@0:     if(br->count < 0)
michael@0:         vp8dx_bool_decoder_fill(br);
michael@0: 
michael@0:     value = br->value;
michael@0:     count = br->count;
michael@0: 
michael@0:     bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
michael@0: 
michael@0:     range = split;
michael@0: 
michael@0:     if (value >= bigsplit)
michael@0:     {
michael@0:         range = br->range - split;
michael@0:         value = value - bigsplit;
michael@0:         bit = 1;
michael@0:     }
michael@0: 
michael@0:     {
michael@0:         register unsigned int shift = vp8_norm[range];
michael@0:         range <<= shift;
michael@0:         value <<= shift;
michael@0:         count -= shift;
michael@0:     }
michael@0:     br->value = value;
michael@0:     br->count = count;
michael@0:     br->range = range;
michael@0: 
michael@0:     return bit;
michael@0: }
michael@0: 
michael@0: static int vp8_decode_value(BOOL_DECODER *br, int bits)
michael@0: {
michael@0:     int z = 0;
michael@0:     int bit;
michael@0: 
michael@0:     for (bit = bits - 1; bit >= 0; bit--)
michael@0:     {
michael@0:         z |= (vp8dx_decode_bool(br, 0x80) << bit);
michael@0:     }
michael@0: 
michael@0:     return z;
michael@0: }
michael@0: 
michael@0: static int vp8dx_bool_error(BOOL_DECODER *br)
michael@0: {
michael@0:     /* Check if we have reached the end of the buffer.
michael@0:      *
michael@0:      * Variable 'count' stores the number of bits in the 'value' buffer, minus
michael@0:      * 8. The top byte is part of the algorithm, and the remainder is buffered
michael@0:      * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
michael@0:      * occupied, 8 for the algorithm and 8 in the buffer.
michael@0:      *
michael@0:      * When reading a byte from the user's buffer, count is filled with 8 and
michael@0:      * one byte is filled into the value buffer. When we reach the end of the
michael@0:      * data, count is additionally filled with VP8_LOTS_OF_BITS. So when
michael@0:      * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
michael@0:      */
michael@0:     if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS))
michael@0:     {
michael@0:        /* We have tried to decode bits after the end of
michael@0:         * stream was encountered.
michael@0:         */
michael@0:         return 1;
michael@0:     }
michael@0: 
michael@0:     /* No error. */
michael@0:     return 0;
michael@0: }
michael@0: 
michael@0: #endif  // DBOOLHUFF_H_