/*
  * Lagarith range decoder
  * Copyright (c) 2009 Nathan Caldwell <saintdev (at) gmail.com>
  * Copyright (c) 2009 David Conrad
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**

  * @file

  * Lagarith range decoder
  * @author Nathan Caldwell
  * @author David Conrad
  */
 
 #ifndef AVCODEC_LAGARITHRAC_H
 #define AVCODEC_LAGARITHRAC_H
 
 #include <stdint.h>
 #include "libavutil/common.h"
 #include "libavutil/intreadwrite.h"
 #include "avcodec.h"
 #include "get_bits.h"
 
 typedef struct lag_rac {
     AVCodecContext *avctx;
     unsigned low;
     unsigned range;

     unsigned scale;             /**< Number of bits of precision in range. */
     unsigned hash_shift;        /**< Number of bits to shift to calculate hash for radix search. */

     const uint8_t *bytestream_start;  /**< Start of input bytestream. */
     const uint8_t *bytestream;        /**< Current position in input bytestream. */
     const uint8_t *bytestream_end;    /**< End position of input bytestream. */

     uint32_t prob[258];         /**< Table of cumulative probability for each symbol. */
     uint8_t  range_hash[256];   /**< Hash table mapping upper byte to approximate symbol. */

 } lag_rac;
 

 void ff_lag_rac_init(lag_rac *l, GetBitContext *gb, int length);

 
 /* TODO: Optimize */
 static inline void lag_rac_refill(lag_rac *l)
 {
     while (l->range <= 0x800000) {
         l->low   <<= 8;
         l->range <<= 8;
         l->low |= 0xff & (AV_RB16(l->bytestream) >> 1);
         if (l->bytestream < l->bytestream_end)
             l->bytestream++;
     }
 }
 
 /**
  * Decode a single byte from the compressed plane described by *l.
  * @param l pointer to lag_rac for the current plane
  * @return next byte of decoded data
  */
 static inline uint8_t lag_get_rac(lag_rac *l)
 {
     unsigned range_scaled, low_scaled, div;
     int val;
     uint8_t shift;
 
     lag_rac_refill(l);
 
     range_scaled = l->range >> l->scale;
 
     if (l->low < range_scaled * l->prob[255]) {
         /* val = 0 is frequent enough to deserve a shortcut */
         if (l->low < range_scaled * l->prob[1]) {
             val = 0;
         } else {
             /* FIXME __builtin_clz is ~20% faster here, but not allowed in generic code. */
             shift = 30 - av_log2(range_scaled);
             div = ((range_scaled << shift) + (1 << 23) - 1) >> 23;
             /* low>>24 ensures that any cases too big for exact FASTDIV are
              * under- rather than over-estimated
              */
             low_scaled = FASTDIV(l->low - (l->low >> 24), div);
             shift -= l->hash_shift;
             shift &= 31;
             low_scaled = (low_scaled << shift) | (low_scaled >> (32 - shift));
             /* low_scaled is now a lower bound of low/range_scaled */
             val = l->range_hash[(uint8_t) low_scaled];
             while (l->low >= range_scaled * l->prob[val + 1])
                 val++;
         }
 
         l->range = range_scaled * (l->prob[val + 1] - l->prob[val]);
     } else {
         val = 255;
         l->range -= range_scaled * l->prob[255];
     }
 

     if (!l->range)
         l->range = 0x80;
 

     l->low -= range_scaled * l->prob[val];
 
     return val;
 }
 
 
 #endif /* AVCODEC_LAGARITHRAC_H */