text: /*
   * Monkey's Audio lossless audio decoder
   * Copyright (c) 2007 Benjamin Zores <ben@geexbox.org>
   *  based upon libdemac from Dave Chapman.
   *
   * 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
   */
  
  #include "libavutil/avassert.h"
  #include "libavutil/channel_layout.h"
  #include "libavutil/opt.h"
  #include "avcodec.h"
  #include "dsputil.h"
  #include "bytestream.h"
  #include "internal.h"
  #include "get_bits.h"
  #include "unary.h"
  
  /**
   * @file
   * Monkey's Audio lossless audio decoder
   */
  
  #define MAX_CHANNELS        2
  #define MAX_BYTESPERSAMPLE  3
  
  #define APE_FRAMECODE_MONO_SILENCE    1
  #define APE_FRAMECODE_STEREO_SILENCE  3
  #define APE_FRAMECODE_PSEUDO_STEREO   4
  
  #define HISTORY_SIZE 512
  #define PREDICTOR_ORDER 8
  /** Total size of all predictor histories */
  #define PREDICTOR_SIZE 50
  
  #define YDELAYA (18 + PREDICTOR_ORDER*4)
  #define YDELAYB (18 + PREDICTOR_ORDER*3)
  #define XDELAYA (18 + PREDICTOR_ORDER*2)
  #define XDELAYB (18 + PREDICTOR_ORDER)
  
  #define YADAPTCOEFFSA 18
  #define XADAPTCOEFFSA 14
  #define YADAPTCOEFFSB 10
  #define XADAPTCOEFFSB 5
  
  /**
   * Possible compression levels
   * @{
   */
  enum APECompressionLevel {
      COMPRESSION_LEVEL_FAST       = 1000,
      COMPRESSION_LEVEL_NORMAL     = 2000,
      COMPRESSION_LEVEL_HIGH       = 3000,
      COMPRESSION_LEVEL_EXTRA_HIGH = 4000,
      COMPRESSION_LEVEL_INSANE     = 5000
  };
  /** @} */
  
  #define APE_FILTER_LEVELS 3
  
  /** Filter orders depending on compression level */
  static const uint16_t ape_filter_orders[5][APE_FILTER_LEVELS] = {
      {  0,   0,    0 },
      { 16,   0,    0 },
      { 64,   0,    0 },
      { 32, 256,    0 },
      { 16, 256, 1280 }
  };
  
  /** Filter fraction bits depending on compression level */
  static const uint8_t ape_filter_fracbits[5][APE_FILTER_LEVELS] = {
      {  0,  0,  0 },
      { 11,  0,  0 },
      { 11,  0,  0 },
      { 10, 13,  0 },
      { 11, 13, 15 }
  };
  
  
  /** Filters applied to the decoded data */
  typedef struct APEFilter {
      int16_t *coeffs;        ///< actual coefficients used in filtering
      int16_t *adaptcoeffs;   ///< adaptive filter coefficients used for correcting of actual filter coefficients
      int16_t *historybuffer; ///< filter memory
      int16_t *delay;         ///< filtered values
  
      int avg;
  } APEFilter;
  
  typedef struct APERice {
      uint32_t k;
      uint32_t ksum;
  } APERice;
  
  typedef struct APERangecoder {
      uint32_t low;           ///< low end of interval
      uint32_t range;         ///< length of interval
      uint32_t help;          ///< bytes_to_follow resp. intermediate value
      unsigned int buffer;    ///< buffer for input/output
  } APERangecoder;
  
  /** Filter histories */
  typedef struct APEPredictor {
      int32_t *buf;
  
      int32_t lastA[2];
  
      int32_t filterA[2];
      int32_t filterB[2];
  
      int32_t coeffsA[2][4];  ///< adaption coefficients
      int32_t coeffsB[2][5];  ///< adaption coefficients
      int32_t historybuffer[HISTORY_SIZE + PREDICTOR_SIZE];
  
      unsigned int sample_pos;
  } APEPredictor;
  
  /** Decoder context */
  typedef struct APEContext {
      AVClass *class;                          ///< class for AVOptions
      AVCodecContext *avctx;
      DSPContext dsp;
      int channels;
      int samples;                             ///< samples left to decode in current frame
      int bps;
  
      int fileversion;                         ///< codec version, very important in decoding process
      int compression_level;                   ///< compression levels
      int fset;                                ///< which filter set to use (calculated from compression level)
      int flags;                               ///< global decoder flags
  
      uint32_t CRC;                            ///< frame CRC
      int frameflags;                          ///< frame flags
      APEPredictor predictor;                  ///< predictor used for final reconstruction
  
      int32_t *decoded_buffer;
      int decoded_size;
      int32_t *decoded[MAX_CHANNELS];          ///< decoded data for each channel
      int blocks_per_loop;                     ///< maximum number of samples to decode for each call
  
      int16_t* filterbuf[APE_FILTER_LEVELS];   ///< filter memory
  
      APERangecoder rc;                        ///< rangecoder used to decode actual values
      APERice riceX;                           ///< rice code parameters for the second channel
      APERice riceY;                           ///< rice code parameters for the first channel
      APEFilter filters[APE_FILTER_LEVELS][2]; ///< filters used for reconstruction
      GetBitContext gb;
  
      uint8_t *data;                           ///< current frame data
      uint8_t *data_end;                       ///< frame data end
      int data_size;                           ///< frame data allocated size
      const uint8_t *ptr;                      ///< current position in frame data
  
      int error;
  
      void (*entropy_decode_mono)(struct APEContext *ctx, int blockstodecode);
      void (*entropy_decode_stereo)(struct APEContext *ctx, int blockstodecode);
      void (*predictor_decode_mono)(struct APEContext *ctx, int count);
      void (*predictor_decode_stereo)(struct APEContext *ctx, int count);
  } APEContext;
  
  static void ape_apply_filters(APEContext *ctx, int32_t *decoded0,
                                int32_t *decoded1, int count);
  
  static void entropy_decode_mono_0000(APEContext *ctx, int blockstodecode);
  static void entropy_decode_stereo_0000(APEContext *ctx, int blockstodecode);
  static void entropy_decode_mono_3860(APEContext *ctx, int blockstodecode);
  static void entropy_decode_stereo_3860(APEContext *ctx, int blockstodecode);
  static void entropy_decode_mono_3900(APEContext *ctx, int blockstodecode);
  static void entropy_decode_stereo_3900(APEContext *ctx, int blockstodecode);
  static void entropy_decode_stereo_3930(APEContext *ctx, int blockstodecode);
  static void entropy_decode_mono_3990(APEContext *ctx, int blockstodecode);
  static void entropy_decode_stereo_3990(APEContext *ctx, int blockstodecode);
  
  static void predictor_decode_mono_3800(APEContext *ctx, int count);
  static void predictor_decode_stereo_3800(APEContext *ctx, int count);
  static void predictor_decode_mono_3930(APEContext *ctx, int count);
  static void predictor_decode_stereo_3930(APEContext *ctx, int count);
  static void predictor_decode_mono_3950(APEContext *ctx, int count);
  static void predictor_decode_stereo_3950(APEContext *ctx, int count);
  
  // TODO: dsputilize
  
  static av_cold int ape_decode_close(AVCodecContext *avctx)
  {
      APEContext *s = avctx->priv_data;
      int i;
  
      for (i = 0; i < APE_FILTER_LEVELS; i++)
          av_freep(&s->filterbuf[i]);
  
      av_freep(&s->decoded_buffer);
      av_freep(&s->data);
      s->decoded_size = s->data_size = 0;
  
      return 0;
  }
  
  static av_cold int ape_decode_init(AVCodecContext *avctx)
  {
      APEContext *s = avctx->priv_data;
      int i;
  
      if (avctx->extradata_size != 6) {
          av_log(avctx, AV_LOG_ERROR, "Incorrect extradata\n");
          return AVERROR(EINVAL);
      }
      if (avctx->channels > 2) {
          av_log(avctx, AV_LOG_ERROR, "Only mono and stereo is supported\n");
          return AVERROR(EINVAL);
      }
      s->bps = avctx->bits_per_coded_sample;
      switch (s->bps) {
      case 8:
          avctx->sample_fmt = AV_SAMPLE_FMT_U8P;
          break;
      case 16:
          avctx->sample_fmt = AV_SAMPLE_FMT_S16P;
          break;
      case 24:
          avctx->sample_fmt = AV_SAMPLE_FMT_S32P;
          break;
      default:
          avpriv_request_sample(avctx,
                                "%d bits per coded sample", s->bps);
          return AVERROR_PATCHWELCOME;
      }
      s->avctx             = avctx;
      s->channels          = avctx->channels;
      s->fileversion       = AV_RL16(avctx->extradata);
      s->compression_level = AV_RL16(avctx->extradata + 2);
      s->flags             = AV_RL16(avctx->extradata + 4);
  
      av_log(avctx, AV_LOG_DEBUG, "Compression Level: %d - Flags: %d\n",
             s->compression_level, s->flags);
      if (s->compression_level % 1000 || s->compression_level > COMPRESSION_LEVEL_INSANE ||
          !s->compression_level ||
          (s->fileversion < 3930 && s->compression_level == COMPRESSION_LEVEL_INSANE)) {
          av_log(avctx, AV_LOG_ERROR, "Incorrect compression level %d\n",
                 s->compression_level);
          return AVERROR_INVALIDDATA;
      }
      s->fset = s->compression_level / 1000 - 1;
      for (i = 0; i < APE_FILTER_LEVELS; i++) {
          if (!ape_filter_orders[s->fset][i])
              break;
          FF_ALLOC_OR_GOTO(avctx, s->filterbuf[i],
                           (ape_filter_orders[s->fset][i] * 3 + HISTORY_SIZE) * 4,
                           filter_alloc_fail);
      }
  
      if (s->fileversion < 3860) {
          s->entropy_decode_mono   = entropy_decode_mono_0000;
          s->entropy_decode_stereo = entropy_decode_stereo_0000;
      } else if (s->fileversion < 3900) {
          s->entropy_decode_mono   = entropy_decode_mono_3860;
          s->entropy_decode_stereo = entropy_decode_stereo_3860;
      } else if (s->fileversion < 3930) {
          s->entropy_decode_mono   = entropy_decode_mono_3900;
          s->entropy_decode_stereo = entropy_decode_stereo_3900;
      } else if (s->fileversion < 3990) {
          s->entropy_decode_mono   = entropy_decode_mono_3900;
          s->entropy_decode_stereo = entropy_decode_stereo_3930;
      } else {
          s->entropy_decode_mono   = entropy_decode_mono_3990;
          s->entropy_decode_stereo = entropy_decode_stereo_3990;
      }
  
      if (s->fileversion < 3930) {
          s->predictor_decode_mono   = predictor_decode_mono_3800;
          s->predictor_decode_stereo = predictor_decode_stereo_3800;
      } else if (s->fileversion < 3950) {
          s->predictor_decode_mono   = predictor_decode_mono_3930;
          s->predictor_decode_stereo = predictor_decode_stereo_3930;
      } else {
          s->predictor_decode_mono   = predictor_decode_mono_3950;
          s->predictor_decode_stereo = predictor_decode_stereo_3950;
      }
  
      ff_dsputil_init(&s->dsp, avctx);
      avctx->channel_layout = (avctx->channels==2) ? AV_CH_LAYOUT_STEREO : AV_CH_LAYOUT_MONO;
  
      return 0;
  filter_alloc_fail:
      ape_decode_close(avctx);
      return AVERROR(ENOMEM);
  }
  
  /**
   * @name APE range decoding functions
   * @{
   */
  
  #define CODE_BITS    32
  #define TOP_VALUE    ((unsigned int)1 << (CODE_BITS-1))
  #define SHIFT_BITS   (CODE_BITS - 9)
  #define EXTRA_BITS   ((CODE_BITS-2) % 8 + 1)
  #define BOTTOM_VALUE (TOP_VALUE >> 8)
  
  /** Start the decoder */
  static inline void range_start_decoding(APEContext *ctx)
  {
      ctx->rc.buffer = bytestream_get_byte(&ctx->ptr);
      ctx->rc.low    = ctx->rc.buffer >> (8 - EXTRA_BITS);
      ctx->rc.range  = (uint32_t) 1 << EXTRA_BITS;
  }
  
  /** Perform normalization */
  static inline void range_dec_normalize(APEContext *ctx)
  {
      while (ctx->rc.range <= BOTTOM_VALUE) {
          ctx->rc.buffer <<= 8;
          if(ctx->ptr < ctx->data_end) {
              ctx->rc.buffer += *ctx->ptr;
              ctx->ptr++;
          } else {
              ctx->error = 1;
          }
          ctx->rc.low    = (ctx->rc.low << 8)    | ((ctx->rc.buffer >> 1) & 0xFF);
          ctx->rc.range  <<= 8;
      }
  }
  
  /**
   * Calculate culmulative frequency for next symbol. Does NO update!
   * @param ctx decoder context
   * @param tot_f is the total frequency or (code_value)1<<shift
   * @return the culmulative frequency
   */
  static inline int range_decode_culfreq(APEContext *ctx, int tot_f)
  {
      range_dec_normalize(ctx);
      ctx->rc.help = ctx->rc.range / tot_f;
      return ctx->rc.low / ctx->rc.help;
  }
  
  /**
   * Decode value with given size in bits
   * @param ctx decoder context
   * @param shift number of bits to decode
   */
  static inline int range_decode_culshift(APEContext *ctx, int shift)
  {
      range_dec_normalize(ctx);
      ctx->rc.help = ctx->rc.range >> shift;
      return ctx->rc.low / ctx->rc.help;
  }
  
  
  /**
   * Update decoding state
   * @param ctx decoder context
   * @param sy_f the interval length (frequency of the symbol)
   * @param lt_f the lower end (frequency sum of < symbols)
   */
  static inline void range_decode_update(APEContext *ctx, int sy_f, int lt_f)
  {
      ctx->rc.low  -= ctx->rc.help * lt_f;
      ctx->rc.range = ctx->rc.help * sy_f;
  }
  
  /** Decode n bits (n <= 16) without modelling */
  static inline int range_decode_bits(APEContext *ctx, int n)
  {
      int sym = range_decode_culshift(ctx, n);
      range_decode_update(ctx, 1, sym);
      return sym;
  }
  
  
  #define MODEL_ELEMENTS 64
  
  /**
   * Fixed probabilities for symbols in Monkey Audio version 3.97
   */
  static const uint16_t counts_3970[22] = {
          0, 14824, 28224, 39348, 47855, 53994, 58171, 60926,
      62682, 63786, 64463, 64878, 65126, 65276, 65365, 65419,
      65450, 65469, 65480, 65487, 65491, 65493,
  };
  
  /**
   * Probability ranges for symbols in Monkey Audio version 3.97
   */
  static const uint16_t counts_diff_3970[21] = {
      14824, 13400, 11124, 8507, 6139, 4177, 2755, 1756,
      1104, 677, 415, 248, 150, 89, 54, 31,
      19, 11, 7, 4, 2,
  };
  
  /**
   * Fixed probabilities for symbols in Monkey Audio version 3.98
   */
  static const uint16_t counts_3980[22] = {
          0, 19578, 36160, 48417, 56323, 60899, 63265, 64435,
      64971, 65232, 65351, 65416, 65447, 65466, 65476, 65482,
      65485, 65488, 65490, 65491, 65492, 65493,
  };
  
  /**
   * Probability ranges for symbols in Monkey Audio version 3.98
   */
  static const uint16_t counts_diff_3980[21] = {
      19578, 16582, 12257, 7906, 4576, 2366, 1170, 536,
      261, 119, 65, 31, 19, 10, 6, 3,
      3, 2, 1, 1, 1,
  };
  
  /**
   * Decode symbol
   * @param ctx decoder context
   * @param counts probability range start position
   * @param counts_diff probability range widths
   */
  static inline int range_get_symbol(APEContext *ctx,
                                     const uint16_t counts[],
                                     const uint16_t counts_diff[])
  {
      int symbol, cf;
  
      cf = range_decode_culshift(ctx, 16);
  
      if(cf > 65492){
          symbol= cf - 65535 + 63;
          range_decode_update(ctx, 1, cf);
          if(cf > 65535)
              ctx->error=1;
          return symbol;
      }
      /* figure out the symbol inefficiently; a binary search would be much better */
      for (symbol = 0; counts[symbol + 1] <= cf; symbol++);
  
      range_decode_update(ctx, counts_diff[symbol], counts[symbol]);
  
      return symbol;
  }
  /** @} */ // group rangecoder
  
  static inline void update_rice(APERice *rice, unsigned int x)
  {
      int lim = rice->k ? (1 << (rice->k + 4)) : 0;
      rice->ksum += ((x + 1) / 2) - ((rice->ksum + 16) >> 5);
  
      if (rice->ksum < lim)
          rice->k--;
      else if (rice->ksum >= (1 << (rice->k + 5)))
          rice->k++;
  }
  
  static inline int get_rice_ook(GetBitContext *gb, int k)
  {
      unsigned int x;
  
      x = get_unary(gb, 1, get_bits_left(gb));
  
      if (k)
          x = (x << k) | get_bits(gb, k);
  
      return x;
  }
  
  static inline int ape_decode_value_3860(APEContext *ctx, GetBitContext *gb,
                                          APERice *rice)
  {
      unsigned int x, overflow;
  
      overflow = get_unary(gb, 1, get_bits_left(gb));
  
      if (ctx->fileversion > 3880) {
          while (overflow >= 16) {
              overflow -= 16;
              rice->k  += 4;
          }
      }
  
      if (!rice->k)
          x = overflow;
      else if(rice->k <= MIN_CACHE_BITS) {
          x = (overflow << rice->k) + get_bits(gb, rice->k);
      } else {
          av_log(ctx->avctx, AV_LOG_ERROR, "Too many bits: %d\n", rice->k);
          return AVERROR_INVALIDDATA;
      }
      rice->ksum += x - (rice->ksum + 8 >> 4);
      if (rice->ksum < (rice->k ? 1 << (rice->k + 4) : 0))
          rice->k--;
      else if (rice->ksum >= (1 << (rice->k + 5)) && rice->k < 24)
          rice->k++;
  
      /* Convert to signed */
      if (x & 1)
          return (x >> 1) + 1;
      else
          return -(x >> 1);
  }
  
  static inline int ape_decode_value_3900(APEContext *ctx, APERice *rice)
  {
      unsigned int x, overflow;
      int tmpk;
  
      overflow = range_get_symbol(ctx, counts_3970, counts_diff_3970);
  
      if (overflow == (MODEL_ELEMENTS - 1)) {
          tmpk = range_decode_bits(ctx, 5);
          overflow = 0;
      } else
          tmpk = (rice->k < 1) ? 0 : rice->k - 1;
  
      if (tmpk <= 16 || ctx->fileversion < 3910) {
          if (tmpk > 23) {
              av_log(ctx->avctx, AV_LOG_ERROR, "Too many bits: %d\n", tmpk);
              return AVERROR_INVALIDDATA;
          }
          x = range_decode_bits(ctx, tmpk);
      } else if (tmpk <= 32) {
          x = range_decode_bits(ctx, 16);
          x |= (range_decode_bits(ctx, tmpk - 16) << 16);
      } else {
          av_log(ctx->avctx, AV_LOG_ERROR, "Too many bits: %d\n", tmpk);
          return AVERROR_INVALIDDATA;
      }
      x += overflow << tmpk;
  
      update_rice(rice, x);
  
      /* Convert to signed */
      if (x & 1)
          return (x >> 1) + 1;
      else
          return -(x >> 1);
  }
  
  static inline int ape_decode_value_3990(APEContext *ctx, APERice *rice)
  {
      unsigned int x, overflow;
      int base, pivot;
  
      pivot = rice->ksum >> 5;
      if (pivot == 0)
          pivot = 1;
  
      overflow = range_get_symbol(ctx, counts_3980, counts_diff_3980);
  
      if (overflow == (MODEL_ELEMENTS - 1)) {
          overflow  = range_decode_bits(ctx, 16) << 16;
          overflow |= range_decode_bits(ctx, 16);
      }
  
      if (pivot < 0x10000) {
          base = range_decode_culfreq(ctx, pivot);
          range_decode_update(ctx, 1, base);
      } else {
          int base_hi = pivot, base_lo;
          int bbits = 0;
  
          while (base_hi & ~0xFFFF) {
              base_hi >>= 1;
              bbits++;
          }
          base_hi = range_decode_culfreq(ctx, base_hi + 1);
          range_decode_update(ctx, 1, base_hi);
          base_lo = range_decode_culfreq(ctx, 1 << bbits);
          range_decode_update(ctx, 1, base_lo);
  
          base = (base_hi << bbits) + base_lo;
      }
  
      x = base + overflow * pivot;
  
      update_rice(rice, x);
  
      /* Convert to signed */
      if (x & 1)
          return (x >> 1) + 1;
      else
          return -(x >> 1);
  }
  
  static void decode_array_0000(APEContext *ctx, GetBitContext *gb,
                                int32_t *out, APERice *rice, int blockstodecode)
  {
      int i;
      int ksummax, ksummin;
  
      rice->ksum = 0;
      for (i = 0; i < 5; i++) {
          out[i] = get_rice_ook(&ctx->gb, 10);
          rice->ksum += out[i];
      }
      rice->k = av_log2(rice->ksum / 10) + 1;
      for (; i < 64; i++) {
          out[i] = get_rice_ook(&ctx->gb, rice->k);
          rice->ksum += out[i];
          rice->k = av_log2(rice->ksum / ((i + 1) * 2)) + 1;
      }
      ksummax = 1 << rice->k + 7;
      ksummin = rice->k ? (1 << rice->k + 6) : 0;
      for (; i < blockstodecode; i++) {
          out[i] = get_rice_ook(&ctx->gb, rice->k);
          rice->ksum += out[i] - out[i - 64];
          while (rice->ksum < ksummin) {
              rice->k--;
              ksummin = rice->k ? ksummin >> 1 : 0;
              ksummax >>= 1;
          }
          while (rice->ksum >= ksummax) {
              rice->k++;
              if (rice->k > 24)
                  return;
              ksummax <<= 1;
              ksummin = ksummin ? ksummin << 1 : 128;
          }
      }
  
      for (i = 0; i < blockstodecode; i++) {
          if (out[i] & 1)
              out[i] = (out[i] >> 1) + 1;
          else
              out[i] = -(out[i] >> 1);
      }
  }
  
  static void entropy_decode_mono_0000(APEContext *ctx, int blockstodecode)
  {
      decode_array_0000(ctx, &ctx->gb, ctx->decoded[0], &ctx->riceY,
                        blockstodecode);
  }
  
  static void entropy_decode_stereo_0000(APEContext *ctx, int blockstodecode)
  {
      decode_array_0000(ctx, &ctx->gb, ctx->decoded[0], &ctx->riceY,
                        blockstodecode);
      decode_array_0000(ctx, &ctx->gb, ctx->decoded[1], &ctx->riceX,
                        blockstodecode);
  }
  
  static void entropy_decode_mono_3860(APEContext *ctx, int blockstodecode)
  {
      int32_t *decoded0 = ctx->decoded[0];
  
      while (blockstodecode--)
          *decoded0++ = ape_decode_value_3860(ctx, &ctx->gb, &ctx->riceY);
  }
  
  static void entropy_decode_stereo_3860(APEContext *ctx, int blockstodecode)
  {
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
      int blocks = blockstodecode;
  
      while (blockstodecode--)
          *decoded0++ = ape_decode_value_3860(ctx, &ctx->gb, &ctx->riceY);
      while (blocks--)
          *decoded1++ = ape_decode_value_3860(ctx, &ctx->gb, &ctx->riceX);
  }
  
  static void entropy_decode_mono_3900(APEContext *ctx, int blockstodecode)
  {
      int32_t *decoded0 = ctx->decoded[0];
  
      while (blockstodecode--)
          *decoded0++ = ape_decode_value_3900(ctx, &ctx->riceY);
  }
  
  static void entropy_decode_stereo_3900(APEContext *ctx, int blockstodecode)
  {
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
      int blocks = blockstodecode;
  
      while (blockstodecode--)
          *decoded0++ = ape_decode_value_3900(ctx, &ctx->riceY);
      range_dec_normalize(ctx);
      // because of some implementation peculiarities we need to backpedal here
      ctx->ptr -= 1;
      range_start_decoding(ctx);
      while (blocks--)
          *decoded1++ = ape_decode_value_3900(ctx, &ctx->riceX);
  }
  
  static void entropy_decode_stereo_3930(APEContext *ctx, int blockstodecode)
  {
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
  
      while (blockstodecode--) {
          *decoded0++ = ape_decode_value_3900(ctx, &ctx->riceY);
          *decoded1++ = ape_decode_value_3900(ctx, &ctx->riceX);
      }
  }
  
  static void entropy_decode_mono_3990(APEContext *ctx, int blockstodecode)
  {
      int32_t *decoded0 = ctx->decoded[0];
  
      while (blockstodecode--)
          *decoded0++ = ape_decode_value_3990(ctx, &ctx->riceY);
  }
  
  static void entropy_decode_stereo_3990(APEContext *ctx, int blockstodecode)
  {
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
  
      while (blockstodecode--) {
          *decoded0++ = ape_decode_value_3990(ctx, &ctx->riceY);
          *decoded1++ = ape_decode_value_3990(ctx, &ctx->riceX);
      }
  }
  
  static int init_entropy_decoder(APEContext *ctx)
  {
      /* Read the CRC */
      if (ctx->fileversion >= 3900) {
          if (ctx->data_end - ctx->ptr < 6)
              return AVERROR_INVALIDDATA;
          ctx->CRC = bytestream_get_be32(&ctx->ptr);
      } else {
          ctx->CRC = get_bits_long(&ctx->gb, 32);
      }
  
      /* Read the frame flags if they exist */
      ctx->frameflags = 0;
      if ((ctx->fileversion > 3820) && (ctx->CRC & 0x80000000)) {
          ctx->CRC &= ~0x80000000;
  
          if (ctx->data_end - ctx->ptr < 6)
              return AVERROR_INVALIDDATA;
          ctx->frameflags = bytestream_get_be32(&ctx->ptr);
      }
  
      /* Initialize the rice structs */
      ctx->riceX.k = 10;
      ctx->riceX.ksum = (1 << ctx->riceX.k) * 16;
      ctx->riceY.k = 10;
      ctx->riceY.ksum = (1 << ctx->riceY.k) * 16;
  
      if (ctx->fileversion >= 3900) {
          /* The first 8 bits of input are ignored. */
          ctx->ptr++;
  
          range_start_decoding(ctx);
      }
  
      return 0;
  }
  
  static const int32_t initial_coeffs_fast_3320[1] = {
      375,
  };
  
  static const int32_t initial_coeffs_a_3800[3] = {
      64, 115, 64,
  };
  
  static const int32_t initial_coeffs_b_3800[2] = {
      740, 0
  };
  
  static const int32_t initial_coeffs_3930[4] = {
      360, 317, -109, 98
  };
  
  static void init_predictor_decoder(APEContext *ctx)
  {
      APEPredictor *p = &ctx->predictor;
  
      /* Zero the history buffers */
      memset(p->historybuffer, 0, PREDICTOR_SIZE * sizeof(*p->historybuffer));
      p->buf = p->historybuffer;
  
      /* Initialize and zero the coefficients */
      if (ctx->fileversion < 3930) {
          if (ctx->compression_level == COMPRESSION_LEVEL_FAST) {
              memcpy(p->coeffsA[0], initial_coeffs_fast_3320,
                     sizeof(initial_coeffs_fast_3320));
              memcpy(p->coeffsA[1], initial_coeffs_fast_3320,
                     sizeof(initial_coeffs_fast_3320));
          } else {
              memcpy(p->coeffsA[0], initial_coeffs_a_3800,
                     sizeof(initial_coeffs_a_3800));
              memcpy(p->coeffsA[1], initial_coeffs_a_3800,
                     sizeof(initial_coeffs_a_3800));
          }
      } else {
          memcpy(p->coeffsA[0], initial_coeffs_3930, sizeof(initial_coeffs_3930));
          memcpy(p->coeffsA[1], initial_coeffs_3930, sizeof(initial_coeffs_3930));
      }
      memset(p->coeffsB, 0, sizeof(p->coeffsB));
      if (ctx->fileversion < 3930) {
          memcpy(p->coeffsB[0], initial_coeffs_b_3800,
                 sizeof(initial_coeffs_b_3800));
          memcpy(p->coeffsB[1], initial_coeffs_b_3800,
                 sizeof(initial_coeffs_b_3800));
      }
  
      p->filterA[0] = p->filterA[1] = 0;
      p->filterB[0] = p->filterB[1] = 0;
      p->lastA[0]   = p->lastA[1]   = 0;
  
      p->sample_pos = 0;
  }
  
  /** Get inverse sign of integer (-1 for positive, 1 for negative and 0 for zero) */
  static inline int APESIGN(int32_t x) {
      return (x < 0) - (x > 0);
  }
  
  static av_always_inline int filter_fast_3320(APEPredictor *p,
                                               const int decoded, const int filter,
                                               const int delayA)
  {
      int32_t predictionA;
  
      p->buf[delayA] = p->lastA[filter];
      if (p->sample_pos < 3) {
          p->lastA[filter]   = decoded;
          p->filterA[filter] = decoded;
          return decoded;
      }
  
      predictionA = p->buf[delayA] * 2 - p->buf[delayA - 1];
      p->lastA[filter] = decoded + (predictionA  * p->coeffsA[filter][0] >> 9);
  
      if ((decoded ^ predictionA) > 0)
          p->coeffsA[filter][0]++;
      else
          p->coeffsA[filter][0]--;
  
      p->filterA[filter] += p->lastA[filter];
  
      return p->filterA[filter];
  }
  
  static av_always_inline int filter_3800(APEPredictor *p,
                                          const int decoded, const int filter,
                                          const int delayA,  const int delayB,
                                          const int start,   const int shift)
  {
      int32_t predictionA, predictionB, sign;
      int32_t d0, d1, d2, d3, d4;
  
      p->buf[delayA] = p->lastA[filter];
      p->buf[delayB] = p->filterB[filter];
      if (p->sample_pos < start) {
          predictionA = decoded + p->filterA[filter];
          p->lastA[filter]   = decoded;
          p->filterB[filter] = decoded;
          p->filterA[filter] = predictionA;
          return predictionA;
      }
      d2 =  p->buf[delayA];
      d1 = (p->buf[delayA] - p->buf[delayA - 1]) << 1;
      d0 =  p->buf[delayA] + ((p->buf[delayA - 2] - p->buf[delayA - 1]) << 3);
      d3 =  p->buf[delayB] * 2 - p->buf[delayB - 1];
      d4 =  p->buf[delayB];
  
      predictionA = d0 * p->coeffsA[filter][0] +
                    d1 * p->coeffsA[filter][1] +
                    d2 * p->coeffsA[filter][2];
  
      sign = APESIGN(decoded);
      p->coeffsA[filter][0] += (((d0 >> 30) & 2) - 1) * sign;
      p->coeffsA[filter][1] += (((d1 >> 28) & 8) - 4) * sign;
      p->coeffsA[filter][2] += (((d2 >> 28) & 8) - 4) * sign;
  
      predictionB = d3 * p->coeffsB[filter][0] -
                    d4 * p->coeffsB[filter][1];
      p->lastA[filter] = decoded + (predictionA >> 11);
      sign = APESIGN(p->lastA[filter]);
      p->coeffsB[filter][0] += (((d3 >> 29) & 4) - 2) * sign;
      p->coeffsB[filter][1] -= (((d4 >> 30) & 2) - 1) * sign;
  
      p->filterB[filter] = p->lastA[filter] + (predictionB >> shift);
      p->filterA[filter] = p->filterB[filter] + ((p->filterA[filter] * 31) >> 5);
  
      return p->filterA[filter];
  }
  
  static void long_filter_high_3800(int32_t *buffer, int order, int shift,
                                    int32_t *coeffs, int32_t *delay, int length)
  {
      int i, j;
      int32_t dotprod, sign;
  
      memset(coeffs, 0, order * sizeof(*coeffs));
      for (i = 0; i < order; i++)
          delay[i] = buffer[i];
      for (i = order; i < length; i++) {
          dotprod = 0;
          sign = APESIGN(buffer[i]);
          for (j = 0; j < order; j++) {
              dotprod += delay[j] * coeffs[j];
              coeffs[j] -= (((delay[j] >> 30) & 2) - 1) * sign;
          }
          buffer[i] -= dotprod >> shift;
          for (j = 0; j < order - 1; j++)
              delay[j] = delay[j + 1];
          delay[order - 1] = buffer[i];
      }
  }
  
  static void long_filter_ehigh_3830(int32_t *buffer, int length)
  {
      int i, j;
      int32_t dotprod, sign;
      int32_t coeffs[8], delay[8];
  
      memset(coeffs, 0, sizeof(coeffs));
      memset(delay,  0, sizeof(delay));
      for (i = 0; i < length; i++) {
          dotprod = 0;
          sign = APESIGN(buffer[i]);
          for (j = 7; j >= 0; j--) {
              dotprod += delay[j] * coeffs[j];
              coeffs[j] -= (((delay[j] >> 30) & 2) - 1) * sign;
          }
          for (j = 7; j > 0; j--)
              delay[j] = delay[j - 1];
          delay[0] = buffer[i];
          buffer[i] -= dotprod >> 9;
      }
  }
  
  static void predictor_decode_stereo_3800(APEContext *ctx, int count)
  {
      APEPredictor *p = &ctx->predictor;
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
      int32_t coeffs[256], delay[256];
      int start = 4, shift = 10;
  
      if (ctx->compression_level == COMPRESSION_LEVEL_HIGH) {
          start = 16;
          long_filter_high_3800(decoded0, 16, 9, coeffs, delay, count);
          long_filter_high_3800(decoded1, 16, 9, coeffs, delay, count);
      } else if (ctx->compression_level == COMPRESSION_LEVEL_EXTRA_HIGH) {
          int order = 128, shift2 = 11;
  
          if (ctx->fileversion >= 3830) {
              order <<= 1;
              shift++;
              shift2++;
              long_filter_ehigh_3830(decoded0 + order, count - order);
              long_filter_ehigh_3830(decoded1 + order, count - order);
          }
          start = order;
          long_filter_high_3800(decoded0, order, shift2, coeffs, delay, count);
          long_filter_high_3800(decoded1, order, shift2, coeffs, delay, count);
      }
  
      while (count--) {
          int X = *decoded0, Y = *decoded1;
          if (ctx->compression_level == COMPRESSION_LEVEL_FAST) {
              *decoded0 = filter_fast_3320(p, Y, 0, YDELAYA);
              decoded0++;
              *decoded1 = filter_fast_3320(p, X, 1, XDELAYA);
              decoded1++;
          } else {
              *decoded0 = filter_3800(p, Y, 0, YDELAYA, YDELAYB,
                                      start, shift);
              decoded0++;
              *decoded1 = filter_3800(p, X, 1, XDELAYA, XDELAYB,
                                      start, shift);
              decoded1++;
          }
  
          /* Combined */
          p->buf++;
          p->sample_pos++;
  
          /* Have we filled the history buffer? */
          if (p->buf == p->historybuffer + HISTORY_SIZE) {
              memmove(p->historybuffer, p->buf,
                      PREDICTOR_SIZE * sizeof(*p->historybuffer));
              p->buf = p->historybuffer;
          }
      }
  }
  
  static void predictor_decode_mono_3800(APEContext *ctx, int count)
  {
      APEPredictor *p = &ctx->predictor;
      int32_t *decoded0 = ctx->decoded[0];
      int32_t coeffs[256], delay[256];
      int start = 4, shift = 10;
  
      if (ctx->compression_level == COMPRESSION_LEVEL_HIGH) {
          start = 16;
          long_filter_high_3800(decoded0, 16, 9, coeffs, delay, count);
      } else if (ctx->compression_level == COMPRESSION_LEVEL_EXTRA_HIGH) {
          int order = 128, shift2 = 11;
  
          if (ctx->fileversion >= 3830) {
              order <<= 1;
              shift++;
              shift2++;
              long_filter_ehigh_3830(decoded0 + order, count - order);
          }
          start = order;
          long_filter_high_3800(decoded0, order, shift2, coeffs, delay, count);
      }
  
      while (count--) {
          if (ctx->compression_level == COMPRESSION_LEVEL_FAST) {
              *decoded0 = filter_fast_3320(p, *decoded0, 0, YDELAYA);
              decoded0++;
          } else {
              *decoded0 = filter_3800(p, *decoded0, 0, YDELAYA, YDELAYB,
                                      start, shift);
              decoded0++;
          }
  
          /* Combined */
          p->buf++;
          p->sample_pos++;
  
          /* Have we filled the history buffer? */
          if (p->buf == p->historybuffer + HISTORY_SIZE) {
              memmove(p->historybuffer, p->buf,
                      PREDICTOR_SIZE * sizeof(*p->historybuffer));
              p->buf = p->historybuffer;
          }
      }
  }
  
  static av_always_inline int predictor_update_3930(APEPredictor *p,
                                                    const int decoded, const int filter,
                                                    const int delayA)
  {
      int32_t predictionA, sign;
      int32_t d0, d1, d2, d3;
  
      p->buf[delayA]     = p->lastA[filter];
      d0 = p->buf[delayA    ];
      d1 = p->buf[delayA    ] - p->buf[delayA - 1];
      d2 = p->buf[delayA - 1] - p->buf[delayA - 2];
      d3 = p->buf[delayA - 2] - p->buf[delayA - 3];
  
      predictionA = d0 * p->coeffsA[filter][0] +
                    d1 * p->coeffsA[filter][1] +
                    d2 * p->coeffsA[filter][2] +
                    d3 * p->coeffsA[filter][3];
  
      p->lastA[filter] = decoded + (predictionA >> 9);
      p->filterA[filter] = p->lastA[filter] + ((p->filterA[filter] * 31) >> 5);
  
      sign = APESIGN(decoded);
      p->coeffsA[filter][0] += ((d0 < 0) * 2 - 1) * sign;
      p->coeffsA[filter][1] += ((d1 < 0) * 2 - 1) * sign;
      p->coeffsA[filter][2] += ((d2 < 0) * 2 - 1) * sign;
      p->coeffsA[filter][3] += ((d3 < 0) * 2 - 1) * sign;
  
      return p->filterA[filter];
  }
  
  static void predictor_decode_stereo_3930(APEContext *ctx, int count)
  {
      APEPredictor *p = &ctx->predictor;
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
  
      ape_apply_filters(ctx, ctx->decoded[0], ctx->decoded[1], count);
  
      while (count--) {
          /* Predictor Y */
          int Y = *decoded1, X = *decoded0;
          *decoded0 = predictor_update_3930(p, Y, 0, YDELAYA);
          decoded0++;
          *decoded1 = predictor_update_3930(p, X, 1, XDELAYA);
          decoded1++;
  
          /* Combined */
          p->buf++;
  
          /* Have we filled the history buffer? */
          if (p->buf == p->historybuffer + HISTORY_SIZE) {
              memmove(p->historybuffer, p->buf,
                      PREDICTOR_SIZE * sizeof(*p->historybuffer));
              p->buf = p->historybuffer;
          }
      }
  }
  
  static void predictor_decode_mono_3930(APEContext *ctx, int count)
  {
      APEPredictor *p = &ctx->predictor;
      int32_t *decoded0 = ctx->decoded[0];
  
      ape_apply_filters(ctx, ctx->decoded[0], NULL, count);
  
      while (count--) {
          *decoded0 = predictor_update_3930(p, *decoded0, 0, YDELAYA);
          decoded0++;
  
          p->buf++;
  
          /* Have we filled the history buffer? */
          if (p->buf == p->historybuffer + HISTORY_SIZE) {
              memmove(p->historybuffer, p->buf,
                      PREDICTOR_SIZE * sizeof(*p->historybuffer));
              p->buf = p->historybuffer;
          }
      }
  }
  
  static av_always_inline int predictor_update_filter(APEPredictor *p,
                                                      const int decoded, const int filter,
                                                      const int delayA,  const int delayB,
                                                      const int adaptA,  const int adaptB)
  {
      int32_t predictionA, predictionB, sign;
  
      p->buf[delayA]     = p->lastA[filter];
      p->buf[adaptA]     = APESIGN(p->buf[delayA]);
      p->buf[delayA - 1] = p->buf[delayA] - p->buf[delayA - 1];
      p->buf[adaptA - 1] = APESIGN(p->buf[delayA - 1]);
  
      predictionA = p->buf[delayA    ] * p->coeffsA[filter][0] +
                    p->buf[delayA - 1] * p->coeffsA[filter][1] +
                    p->buf[delayA - 2] * p->coeffsA[filter][2] +
                    p->buf[delayA - 3] * p->coeffsA[filter][3];
  
      /*  Apply a scaled first-order filter compression */
      p->buf[delayB]     = p->filterA[filter ^ 1] - ((p->filterB[filter] * 31) >> 5);
      p->buf[adaptB]     = APESIGN(p->buf[delayB]);
      p->buf[delayB - 1] = p->buf[delayB] - p->buf[delayB - 1];
      p->buf[adaptB - 1] = APESIGN(p->buf[delayB - 1]);
      p->filterB[filter] = p->filterA[filter ^ 1];
  
      predictionB = p->buf[delayB    ] * p->coeffsB[filter][0] +
                    p->buf[delayB - 1] * p->coeffsB[filter][1] +
                    p->buf[delayB - 2] * p->coeffsB[filter][2] +
                    p->buf[delayB - 3] * p->coeffsB[filter][3] +
                    p->buf[delayB - 4] * p->coeffsB[filter][4];
  
      p->lastA[filter] = decoded + ((predictionA + (predictionB >> 1)) >> 10);
      p->filterA[filter] = p->lastA[filter] + ((p->filterA[filter] * 31) >> 5);
  
      sign = APESIGN(decoded);
      p->coeffsA[filter][0] += p->buf[adaptA    ] * sign;
      p->coeffsA[filter][1] += p->buf[adaptA - 1] * sign;
      p->coeffsA[filter][2] += p->buf[adaptA - 2] * sign;
      p->coeffsA[filter][3] += p->buf[adaptA - 3] * sign;
      p->coeffsB[filter][0] += p->buf[adaptB    ] * sign;
      p->coeffsB[filter][1] += p->buf[adaptB - 1] * sign;
      p->coeffsB[filter][2] += p->buf[adaptB - 2] * sign;
      p->coeffsB[filter][3] += p->buf[adaptB - 3] * sign;
      p->coeffsB[filter][4] += p->buf[adaptB - 4] * sign;
  
      return p->filterA[filter];
  }
  
  static void predictor_decode_stereo_3950(APEContext *ctx, int count)
  {
      APEPredictor *p = &ctx->predictor;
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
  
      ape_apply_filters(ctx, ctx->decoded[0], ctx->decoded[1], count);
  
      while (count--) {
          /* Predictor Y */
          *decoded0 = predictor_update_filter(p, *decoded0, 0, YDELAYA, YDELAYB,
                                              YADAPTCOEFFSA, YADAPTCOEFFSB);
          decoded0++;
          *decoded1 = predictor_update_filter(p, *decoded1, 1, XDELAYA, XDELAYB,
                                              XADAPTCOEFFSA, XADAPTCOEFFSB);
          decoded1++;
  
          /* Combined */
          p->buf++;
  
          /* Have we filled the history buffer? */
          if (p->buf == p->historybuffer + HISTORY_SIZE) {
              memmove(p->historybuffer, p->buf,
                      PREDICTOR_SIZE * sizeof(*p->historybuffer));
              p->buf = p->historybuffer;
          }
      }
  }
  
  static void predictor_decode_mono_3950(APEContext *ctx, int count)
  {
      APEPredictor *p = &ctx->predictor;
      int32_t *decoded0 = ctx->decoded[0];
      int32_t predictionA, currentA, A, sign;
  
      ape_apply_filters(ctx, ctx->decoded[0], NULL, count);
  
      currentA = p->lastA[0];
  
      while (count--) {
          A = *decoded0;
  
          p->buf[YDELAYA] = currentA;
          p->buf[YDELAYA - 1] = p->buf[YDELAYA] - p->buf[YDELAYA - 1];
  
          predictionA = p->buf[YDELAYA    ] * p->coeffsA[0][0] +
                        p->buf[YDELAYA - 1] * p->coeffsA[0][1] +
                        p->buf[YDELAYA - 2] * p->coeffsA[0][2] +
                        p->buf[YDELAYA - 3] * p->coeffsA[0][3];
  
          currentA = A + (predictionA >> 10);
  
          p->buf[YADAPTCOEFFSA]     = APESIGN(p->buf[YDELAYA    ]);
          p->buf[YADAPTCOEFFSA - 1] = APESIGN(p->buf[YDELAYA - 1]);
  
          sign = APESIGN(A);
          p->coeffsA[0][0] += p->buf[YADAPTCOEFFSA    ] * sign;
          p->coeffsA[0][1] += p->buf[YADAPTCOEFFSA - 1] * sign;
          p->coeffsA[0][2] += p->buf[YADAPTCOEFFSA - 2] * sign;
          p->coeffsA[0][3] += p->buf[YADAPTCOEFFSA - 3] * sign;
  
          p->buf++;
  
          /* Have we filled the history buffer? */
          if (p->buf == p->historybuffer + HISTORY_SIZE) {
              memmove(p->historybuffer, p->buf,
                      PREDICTOR_SIZE * sizeof(*p->historybuffer));
              p->buf = p->historybuffer;
          }
  
          p->filterA[0] = currentA + ((p->filterA[0] * 31) >> 5);
          *(decoded0++) = p->filterA[0];
      }
  
      p->lastA[0] = currentA;
  }
  
  static void do_init_filter(APEFilter *f, int16_t *buf, int order)
  {
      f->coeffs = buf;
      f->historybuffer = buf + order;
      f->delay       = f->historybuffer + order * 2;
      f->adaptcoeffs = f->historybuffer + order;
  
      memset(f->historybuffer, 0, (order * 2) * sizeof(*f->historybuffer));
      memset(f->coeffs, 0, order * sizeof(*f->coeffs));
      f->avg = 0;
  }
  
  static void init_filter(APEContext *ctx, APEFilter *f, int16_t *buf, int order)
  {
      do_init_filter(&f[0], buf, order);
      do_init_filter(&f[1], buf + order * 3 + HISTORY_SIZE, order);
  }
  
  static void do_apply_filter(APEContext *ctx, int version, APEFilter *f,
                              int32_t *data, int count, int order, int fracbits)
  {
      int res;
      int absres;
  
      while (count--) {
          /* round fixedpoint scalar product */
          res = ctx->dsp.scalarproduct_and_madd_int16(f->coeffs, f->delay - order,
                                                      f->adaptcoeffs - order,
                                                      order, APESIGN(*data));
          res = (res + (1 << (fracbits - 1))) >> fracbits;
          res += *data;
          *data++ = res;
  
          /* Update the output history */
          *f->delay++ = av_clip_int16(res);
  
          if (version < 3980) {
              /* Version ??? to < 3.98 files (untested) */
              f->adaptcoeffs[0]  = (res == 0) ? 0 : ((res >> 28) & 8) - 4;
              f->adaptcoeffs[-4] >>= 1;
              f->adaptcoeffs[-8] >>= 1;
          } else {
              /* Version 3.98 and later files */
  
              /* Update the adaption coefficients */
              absres = FFABS(res);
              if (absres)
                  *f->adaptcoeffs = ((res & (-1<<31)) ^ (-1<<30)) >>
                                    (25 + (absres <= f->avg*3) + (absres <= f->avg*4/3));
              else
                  *f->adaptcoeffs = 0;
  
              f->avg += (absres - f->avg) / 16;
  
              f->adaptcoeffs[-1] >>= 1;
              f->adaptcoeffs[-2] >>= 1;
              f->adaptcoeffs[-8] >>= 1;
          }
  
          f->adaptcoeffs++;
  
          /* Have we filled the history buffer? */
          if (f->delay == f->historybuffer + HISTORY_SIZE + (order * 2)) {
              memmove(f->historybuffer, f->delay - (order * 2),
                      (order * 2) * sizeof(*f->historybuffer));
              f->delay = f->historybuffer + order * 2;
              f->adaptcoeffs = f->historybuffer + order;
          }
      }
  }
  
  static void apply_filter(APEContext *ctx, APEFilter *f,
                           int32_t *data0, int32_t *data1,
                           int count, int order, int fracbits)
  {
      do_apply_filter(ctx, ctx->fileversion, &f[0], data0, count, order, fracbits);
      if (data1)
          do_apply_filter(ctx, ctx->fileversion, &f[1], data1, count, order, fracbits);
  }
  
  static void ape_apply_filters(APEContext *ctx, int32_t *decoded0,
                                int32_t *decoded1, int count)
  {
      int i;
  
      for (i = 0; i < APE_FILTER_LEVELS; i++) {
          if (!ape_filter_orders[ctx->fset][i])
              break;
          apply_filter(ctx, ctx->filters[i], decoded0, decoded1, count,
                       ape_filter_orders[ctx->fset][i],
                       ape_filter_fracbits[ctx->fset][i]);
      }
  }
  
  static int init_frame_decoder(APEContext *ctx)
  {
      int i, ret;
      if ((ret = init_entropy_decoder(ctx)) < 0)
          return ret;
      init_predictor_decoder(ctx);
  
      for (i = 0; i < APE_FILTER_LEVELS; i++) {
          if (!ape_filter_orders[ctx->fset][i])
              break;
          init_filter(ctx, ctx->filters[i], ctx->filterbuf[i],
                      ape_filter_orders[ctx->fset][i]);
      }
      return 0;
  }
  
  static void ape_unpack_mono(APEContext *ctx, int count)
  {
      if (ctx->frameflags & APE_FRAMECODE_STEREO_SILENCE) {
          /* We are pure silence, so we're done. */
          av_log(ctx->avctx, AV_LOG_DEBUG, "pure silence mono\n");
          return;
      }
  
      ctx->entropy_decode_mono(ctx, count);
  
      /* Now apply the predictor decoding */
      ctx->predictor_decode_mono(ctx, count);
  
      /* Pseudo-stereo - just copy left channel to right channel */
      if (ctx->channels == 2) {
          memcpy(ctx->decoded[1], ctx->decoded[0], count * sizeof(*ctx->decoded[1]));
      }
  }
  
  static void ape_unpack_stereo(APEContext *ctx, int count)
  {
      int32_t left, right;
      int32_t *decoded0 = ctx->decoded[0];
      int32_t *decoded1 = ctx->decoded[1];
  
      if (ctx->frameflags & APE_FRAMECODE_STEREO_SILENCE) {
          /* We are pure silence, so we're done. */
          av_log(ctx->avctx, AV_LOG_DEBUG, "pure silence stereo\n");
          return;
      }
  
      ctx->entropy_decode_stereo(ctx, count);
  
      /* Now apply the predictor decoding */
      ctx->predictor_decode_stereo(ctx, count);
  
      /* Decorrelate and scale to output depth */
      while (count--) {
          left = *decoded1 - (*decoded0 / 2);
          right = left + *decoded0;
  
          *(decoded0++) = left;
          *(decoded1++) = right;
      }
  }
  
  static int ape_decode_frame(AVCodecContext *avctx, void *data,
                              int *got_frame_ptr, AVPacket *avpkt)
  {
      AVFrame *frame     = data;
      const uint8_t *buf = avpkt->data;
      APEContext *s = avctx->priv_data;
      uint8_t *sample8;
      int16_t *sample16;
      int32_t *sample24;
      int i, ch, ret;
      int blockstodecode;
  
      /* this should never be negative, but bad things will happen if it is, so
         check it just to make sure. */
      av_assert0(s->samples >= 0);
  
      if(!s->samples){
          uint32_t nblocks, offset;
          int buf_size;
  
          if (!avpkt->size) {
              *got_frame_ptr = 0;
              return 0;
          }
          if (avpkt->size < 8) {
              av_log(avctx, AV_LOG_ERROR, "Packet is too small\n");
              return AVERROR_INVALIDDATA;
          }
          buf_size = avpkt->size & ~3;
          if (buf_size != avpkt->size) {
              av_log(avctx, AV_LOG_WARNING, "packet size is not a multiple of 4. "
                     "extra bytes at the end will be skipped.\n");
          }
          if (s->fileversion < 3950) // previous versions overread two bytes
              buf_size += 2;
          av_fast_malloc(&s->data, &s->data_size, buf_size);
          if (!s->data)
              return AVERROR(ENOMEM);
          s->dsp.bswap_buf((uint32_t*)s->data, (const uint32_t*)buf, buf_size >> 2);
          memset(s->data + (buf_size & ~3), 0, buf_size & 3);
          s->ptr = s->data;
          s->data_end = s->data + buf_size;
  
          nblocks = bytestream_get_be32(&s->ptr);
          offset  = bytestream_get_be32(&s->ptr);
          if (s->fileversion >= 3900) {
              if (offset > 3) {
                  av_log(avctx, AV_LOG_ERROR, "Incorrect offset passed\n");
                  s->data = NULL;
                  return AVERROR_INVALIDDATA;
              }
              if (s->data_end - s->ptr < offset) {
                  av_log(avctx, AV_LOG_ERROR, "Packet is too small\n");
                  return AVERROR_INVALIDDATA;
              }
              s->ptr += offset;
          } else {
              init_get_bits(&s->gb, s->ptr, (s->data_end - s->ptr) * 8);
              if (s->fileversion > 3800)
                  skip_bits_long(&s->gb, offset * 8);
              else
                  skip_bits_long(&s->gb, offset);
          }
  
          if (!nblocks || nblocks > INT_MAX) {
              av_log(avctx, AV_LOG_ERROR, "Invalid sample count: %u.\n", nblocks);
              return AVERROR_INVALIDDATA;
          }
          s->samples = nblocks;
  
          /* Initialize the frame decoder */
          if (init_frame_decoder(s) < 0) {
              av_log(avctx, AV_LOG_ERROR, "Error reading frame header\n");
              return AVERROR_INVALIDDATA;
          }
      }
  
      if (!s->data) {
          *got_frame_ptr = 0;
          return avpkt->size;
      }
  
      blockstodecode = FFMIN(s->blocks_per_loop, s->samples);
      // for old files coefficients were not interleaved,
      // so we need to decode all of them at once
      if (s->fileversion < 3930)
          blockstodecode = s->samples;
  
      /* reallocate decoded sample buffer if needed */
      av_fast_malloc(&s->decoded_buffer, &s->decoded_size,
                     2 * FFALIGN(blockstodecode, 8) * sizeof(*s->decoded_buffer));
      if (!s->decoded_buffer)
          return AVERROR(ENOMEM);
      memset(s->decoded_buffer, 0, s->decoded_size);
      s->decoded[0] = s->decoded_buffer;
      s->decoded[1] = s->decoded_buffer + FFALIGN(blockstodecode, 8);
  
      /* get output buffer */
      frame->nb_samples = blockstodecode;
      if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
          return ret;
  
      s->error=0;
  
      if ((s->channels == 1) || (s->frameflags & APE_FRAMECODE_PSEUDO_STEREO))
          ape_unpack_mono(s, blockstodecode);
      else
          ape_unpack_stereo(s, blockstodecode);
      emms_c();
  
      if (s->error) {
          s->samples=0;
          av_log(avctx, AV_LOG_ERROR, "Error decoding frame\n");
          return AVERROR_INVALIDDATA;
      }
  
      switch (s->bps) {
      case 8:
          for (ch = 0; ch < s->channels; ch++) {
              sample8 = (uint8_t *)frame->data[ch];
              for (i = 0; i < blockstodecode; i++)
                  *sample8++ = (s->decoded[ch][i] + 0x80) & 0xff;
          }
          break;
      case 16:
          for (ch = 0; ch < s->channels; ch++) {
              sample16 = (int16_t *)frame->data[ch];
              for (i = 0; i < blockstodecode; i++)
                  *sample16++ = s->decoded[ch][i];
          }
          break;
      case 24:
          for (ch = 0; ch < s->channels; ch++) {
              sample24 = (int32_t *)frame->data[ch];
              for (i = 0; i < blockstodecode; i++)
                  *sample24++ = s->decoded[ch][i] << 8;
          }
          break;
      }
  
      s->samples -= blockstodecode;
  
      *got_frame_ptr = 1;
  
      return !s->samples ? avpkt->size : 0;
  }
  
  static void ape_flush(AVCodecContext *avctx)
  {
      APEContext *s = avctx->priv_data;
      s->samples= 0;
  }
  
  #define OFFSET(x) offsetof(APEContext, x)
  #define PAR (AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_AUDIO_PARAM)
  static const AVOption options[] = {
      { "max_samples", "maximum number of samples decoded per call",             OFFSET(blocks_per_loop), AV_OPT_TYPE_INT,   { .i64 = 4608 },    1,       INT_MAX, PAR, "max_samples" },
      { "all",         "no maximum. decode all samples for each packet at once", 0,                       AV_OPT_TYPE_CONST, { .i64 = INT_MAX }, INT_MIN, INT_MAX, PAR, "max_samples" },
      { NULL},
  };
  
  static const AVClass ape_decoder_class = {
      .class_name = "APE decoder",
      .item_name  = av_default_item_name,
      .option     = options,
      .version    = LIBAVUTIL_VERSION_INT,
  };
  
  AVCodec ff_ape_decoder = {
      .name           = "ape",
      .type           = AVMEDIA_TYPE_AUDIO,
      .id             = AV_CODEC_ID_APE,
      .priv_data_size = sizeof(APEContext),
      .init           = ape_decode_init,
      .close          = ape_decode_close,
      .decode         = ape_decode_frame,
      .capabilities   = CODEC_CAP_SUBFRAMES | CODEC_CAP_DELAY | CODEC_CAP_DR1,
      .flush          = ape_flush,
      .long_name      = NULL_IF_CONFIG_SMALL("Monkey's Audio"),
      .sample_fmts    = (const enum AVSampleFormat[]) { AV_SAMPLE_FMT_U8P,
                                                        AV_SAMPLE_FMT_S16P,
                                                        AV_SAMPLE_FMT_S32P,
                                                        AV_SAMPLE_FMT_NONE },
      .priv_class     = &ape_decoder_class,
  };
  