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 /*

  *  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 DBOOLHUFF_H_

 #define DBOOLHUFF_H_

 #include <stddef.h>

 #include <limits.h>

 #include "vpx_config.h"

 #include "vpx_ports/mem.h"

 #include "vpx/vpx_integer.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)

 /*Decrypt n bytes of data from input -> output, using the decrypt_state

    passed in VP8D_SET_DECRYPTOR.

 */

 typedef void (vp8_decrypt_cb)(void *decrypt_state, const unsigned char *input,

                               unsigned char *output, int count);

 typedef struct

 {

     const unsigned char *user_buffer_end;

     const unsigned char *user_buffer;

     VP8_BD_VALUE         value;

     int                  count;

     unsigned int         range;

     vp8_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,

                        vp8_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 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 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  // DBOOLHUFF_H_