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words.c

////////////////////////////////////////////////////////////////////////////
//                           **** WAVPACK ****                            //
//                  Hybrid Lossless Wavefile Compressor                   //
//              Copyright (c) 1998 - 2006 Conifer Software.               //
//                          All Rights Reserved.                          //
////////////////////////////////////////////////////////////////////////////

// words.c

// This module provides entropy word encoding and decoding functions using
// a variation on the Rice method.  This was introduced in version 3.93
// because it allows splitting the data into a "lossy" stream and a
// "correction" stream in a very efficient manner and is therefore ideal
// for the "hybrid" mode.  For 4.0, the efficiency of this method was
// significantly improved by moving away from the normal Rice restriction of
// using powers of two for the modulus divisions and now the method can be
// used for both hybrid and pure lossless encoding.

// Samples are divided by median probabilities at 5/7 (71.43%), 10/49 (20.41%),
// and 20/343 (5.83%). Each zone has 3.5 times fewer samples than the
// previous. Using standard Rice coding on this data would result in 1.4
// bits per sample average (not counting sign bit). However, there is a
// very simple encoding that is over 99% efficient with this data and
// results in about 1.22 bits per sample.

#include "wavpack_local.h"

#include <stdlib.h>
#include <string.h>

#ifdef DEBUG_ALLOC
#define malloc malloc_db
#define realloc realloc_db
#define free free_db
void *malloc_db (uint32_t size);
void *realloc_db (void *ptr, uint32_t size);
void free_db (void *ptr);
int32_t dump_alloc (void);
#endif

// #define DEBUG_WORDS  // debug module by sending all 32 bits literally

//////////////////////////////// local macros /////////////////////////////////

#define LIMIT_ONES 16   // maximum consecutive 1s sent for "div" data

// these control the time constant "slow_level" which is used for hybrid mode
// that controls bitrate as a function of residual level (HYBRID_BITRATE).
#define SLS 8
#define SLO ((1 << (SLS - 1)))

// these control the time constant of the 3 median level breakpoints
#define DIV0 128  // 5/7 of samples
#define DIV1 64         // 10/49 of samples
#define DIV2 32         // 20/343 of samples

// this macro retrieves the specified median breakpoint (without frac; min = 1)
#define GET_MED(med) (((wps->w.median [med] [chan]) >> 4) + 1)

// These macros update the specified median breakpoints. Note that the median
// is incremented when the sample is higher than the median, else decremented.
// They are designed so that the median will never drop below 1 and the value
// is essentially stationary if there are 2 increments for every 5 decrements.

#define INC_MED0() (wps->w.median [0] [chan] += ((wps->w.median [0] [chan] + DIV0) / DIV0) * 5)
#define DEC_MED0() (wps->w.median [0] [chan] -= ((wps->w.median [0] [chan] + (DIV0-2)) / DIV0) * 2)
#define INC_MED1() (wps->w.median [1] [chan] += ((wps->w.median [1] [chan] + DIV1) / DIV1) * 5)
#define DEC_MED1() (wps->w.median [1] [chan] -= ((wps->w.median [1] [chan] + (DIV1-2)) / DIV1) * 2)
#define INC_MED2() (wps->w.median [2] [chan] += ((wps->w.median [2] [chan] + DIV2) / DIV2) * 5)
#define DEC_MED2() (wps->w.median [2] [chan] -= ((wps->w.median [2] [chan] + (DIV2-2)) / DIV2) * 2)

#define count_bits(av) ( \
 (av) < (1 << 8) ? nbits_table [av] : \
  ( \
   (av) < (1L << 16) ? nbits_table [(av) >> 8] + 8 : \
   ((av) < (1L << 24) ? nbits_table [(av) >> 16] + 16 : nbits_table [(av) >> 24] + 24) \
  ) \
)

///////////////////////////// local table storage ////////////////////////////

const uint32_t bitset [] = {
    1L << 0, 1L << 1, 1L << 2, 1L << 3,
    1L << 4, 1L << 5, 1L << 6, 1L << 7,
    1L << 8, 1L << 9, 1L << 10, 1L << 11,
    1L << 12, 1L << 13, 1L << 14, 1L << 15,
    1L << 16, 1L << 17, 1L << 18, 1L << 19,
    1L << 20, 1L << 21, 1L << 22, 1L << 23,
    1L << 24, 1L << 25, 1L << 26, 1L << 27,
    1L << 28, 1L << 29, 1L << 30, 1L << 31
};

const uint32_t bitmask [] = {
    (1L << 0) - 1, (1L << 1) - 1, (1L << 2) - 1, (1L << 3) - 1,
    (1L << 4) - 1, (1L << 5) - 1, (1L << 6) - 1, (1L << 7) - 1,
    (1L << 8) - 1, (1L << 9) - 1, (1L << 10) - 1, (1L << 11) - 1,
    (1L << 12) - 1, (1L << 13) - 1, (1L << 14) - 1, (1L << 15) - 1,
    (1L << 16) - 1, (1L << 17) - 1, (1L << 18) - 1, (1L << 19) - 1,
    (1L << 20) - 1, (1L << 21) - 1, (1L << 22) - 1, (1L << 23) - 1,
    (1L << 24) - 1, (1L << 25) - 1, (1L << 26) - 1, (1L << 27) - 1,
    (1L << 28) - 1, (1L << 29) - 1, (1L << 30) - 1, 0x7fffffff
};

const char nbits_table [] = {
    0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,   // 0 - 15
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,   // 16 - 31
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,   // 32 - 47
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,   // 48 - 63
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,   // 64 - 79
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,   // 80 - 95
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,   // 96 - 111
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,   // 112 - 127
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,   // 128 - 143
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,   // 144 - 159
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,   // 160 - 175
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,   // 176 - 191
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,   // 192 - 207
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,   // 208 - 223
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,   // 224 - 239
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8    // 240 - 255
};

static const uchar log2_table [] = {
    0x00, 0x01, 0x03, 0x04, 0x06, 0x07, 0x09, 0x0a, 0x0b, 0x0d, 0x0e, 0x10, 0x11, 0x12, 0x14, 0x15,
    0x16, 0x18, 0x19, 0x1a, 0x1c, 0x1d, 0x1e, 0x20, 0x21, 0x22, 0x24, 0x25, 0x26, 0x28, 0x29, 0x2a,
    0x2c, 0x2d, 0x2e, 0x2f, 0x31, 0x32, 0x33, 0x34, 0x36, 0x37, 0x38, 0x39, 0x3b, 0x3c, 0x3d, 0x3e,
    0x3f, 0x41, 0x42, 0x43, 0x44, 0x45, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4d, 0x4e, 0x4f, 0x50, 0x51,
    0x52, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63,
    0x64, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x74, 0x75,
    0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85,
    0x86, 0x87, 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95,
    0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4,
    0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb0, 0xb1, 0xb2, 0xb2,
    0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf, 0xc0, 0xc0,
    0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xcb, 0xcb, 0xcc, 0xcd, 0xce,
    0xcf, 0xd0, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd8, 0xd9, 0xda, 0xdb,
    0xdc, 0xdc, 0xdd, 0xde, 0xdf, 0xe0, 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe4, 0xe5, 0xe6, 0xe7, 0xe7,
    0xe8, 0xe9, 0xea, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xee, 0xef, 0xf0, 0xf1, 0xf1, 0xf2, 0xf3, 0xf4,
    0xf4, 0xf5, 0xf6, 0xf7, 0xf7, 0xf8, 0xf9, 0xf9, 0xfa, 0xfb, 0xfc, 0xfc, 0xfd, 0xfe, 0xff, 0xff
};

static const uchar exp2_table [] = {
    0x00, 0x01, 0x01, 0x02, 0x03, 0x03, 0x04, 0x05, 0x06, 0x06, 0x07, 0x08, 0x08, 0x09, 0x0a, 0x0b,
    0x0b, 0x0c, 0x0d, 0x0e, 0x0e, 0x0f, 0x10, 0x10, 0x11, 0x12, 0x13, 0x13, 0x14, 0x15, 0x16, 0x16,
    0x17, 0x18, 0x19, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1d, 0x1e, 0x1f, 0x20, 0x20, 0x21, 0x22, 0x23,
    0x24, 0x24, 0x25, 0x26, 0x27, 0x28, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,
    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3a, 0x3b, 0x3c, 0x3d,
    0x3e, 0x3f, 0x40, 0x41, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x48, 0x49, 0x4a, 0x4b,
    0x4c, 0x4d, 0x4e, 0x4f, 0x50, 0x51, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
    0x5b, 0x5c, 0x5d, 0x5e, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
    0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,
    0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x87, 0x88, 0x89, 0x8a,
    0x8b, 0x8c, 0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b,
    0x9c, 0x9d, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad,
    0xaf, 0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xbc, 0xbd, 0xbe, 0xbf, 0xc0,
    0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc8, 0xc9, 0xca, 0xcb, 0xcd, 0xce, 0xcf, 0xd0, 0xd2, 0xd3, 0xd4,
    0xd6, 0xd7, 0xd8, 0xd9, 0xdb, 0xdc, 0xdd, 0xde, 0xe0, 0xe1, 0xe2, 0xe4, 0xe5, 0xe6, 0xe8, 0xe9,
    0xea, 0xec, 0xed, 0xee, 0xf0, 0xf1, 0xf2, 0xf4, 0xf5, 0xf6, 0xf8, 0xf9, 0xfa, 0xfc, 0xfd, 0xff
};

static const char ones_count_table [] = {
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,6,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,7,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,6,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,8
};

///////////////////////////// executable code ////////////////////////////////

static int FASTCALL mylog2 (uint32_t avalue);

// Initialize entropy encoder for the specified stream. In lossless mode there
// are no parameters to select; in hybrid mode the bitrate mode and value need
// be initialized.

#ifndef NO_PACK

void init_words (WavpackStream *wps)
{
    CLEAR (wps->w);

    if (wps->wphdr.flags & HYBRID_FLAG)
      word_set_bitrate (wps);
}

// Set up parameters for hybrid mode based on header flags and "bits" field.
// This is currently only set up for the HYBRID_BITRATE mode in which the
// allowed error varies with the residual level (from "slow_level"). The
// simpler mode (which is not used yet) has the error level directly
// controlled from the metadata.

void word_set_bitrate (WavpackStream *wps)
{
    int bitrate_0, bitrate_1;

    if (wps->wphdr.flags & HYBRID_BITRATE) {
      if (wps->wphdr.flags & FALSE_STEREO)
          bitrate_0 = (wps->bits * 2 - 512) < 568 ? 0 : (wps->bits * 2 - 512) - 568;
      else
          bitrate_0 = wps->bits < 568 ? 0 : wps->bits - 568;

      if (!(wps->wphdr.flags & MONO_DATA)) {

          if (wps->wphdr.flags & HYBRID_BALANCE)
            bitrate_1 = (wps->wphdr.flags & JOINT_STEREO) ? 256 : 0;
          else {
            bitrate_1 = bitrate_0;

            if (wps->wphdr.flags & JOINT_STEREO) {
                if (bitrate_0 < 128) {
                  bitrate_1 += bitrate_0;
                  bitrate_0 = 0;
                }
                else {
                  bitrate_0 -= 128;
                  bitrate_1 += 128;
                }
            }
          }
      }
        else
            bitrate_1 = 0;
    }
    else
      bitrate_0 = bitrate_1 = 0;

    wps->w.bitrate_acc [0] = (int32_t) bitrate_0 << 16;
    wps->w.bitrate_acc [1] = (int32_t) bitrate_1 << 16;
}

// Allocates the correct space in the metadata structure and writes the
// current median values to it. Values are converted from 32-bit unsigned
// to our internal 16-bit mylog2 values, and read_entropy_vars () is called
// to read the values back because we must compensate for the loss through
// the log function.

void write_entropy_vars (WavpackStream *wps, WavpackMetadata *wpmd)
{
    uchar *byteptr;
    int temp;

    byteptr = wpmd->data = malloc (12);
    wpmd->id = ID_ENTROPY_VARS;

    *byteptr++ = temp = mylog2 (wps->w.median [0] [0]);
    *byteptr++ = temp >> 8;
    *byteptr++ = temp = mylog2 (wps->w.median [1] [0]);
    *byteptr++ = temp >> 8;
    *byteptr++ = temp = mylog2 (wps->w.median [2] [0]);
    *byteptr++ = temp >> 8;

    if (!(wps->wphdr.flags & MONO_DATA)) {
      *byteptr++ = temp = mylog2 (wps->w.median [0] [1]);
      *byteptr++ = temp >> 8;
      *byteptr++ = temp = mylog2 (wps->w.median [1] [1]);
      *byteptr++ = temp >> 8;
      *byteptr++ = temp = mylog2 (wps->w.median [2] [1]);
      *byteptr++ = temp >> 8;
    }

    wpmd->byte_length = (int32_t)(byteptr - (uchar *) wpmd->data);
    read_entropy_vars (wps, wpmd);
}

// Allocates enough space in the metadata structure and writes the current
// high word of the bitrate accumulator and the slow_level values to it. The
// slow_level values are converted from 32-bit unsigned to our internal 16-bit
// mylog2 values. Afterward, read_entropy_vars () is called to read the values
// back because we must compensate for the loss through the log function and
// the truncation of the bitrate.

void write_hybrid_profile (WavpackStream *wps, WavpackMetadata *wpmd)
{
    uchar *byteptr;
    int temp;

    word_set_bitrate (wps);
    byteptr = wpmd->data = malloc (512);
    wpmd->id = ID_HYBRID_PROFILE;

    if (wps->wphdr.flags & HYBRID_BITRATE) {
      *byteptr++ = temp = log2s (wps->w.slow_level [0]);
      *byteptr++ = temp >> 8;

      if (!(wps->wphdr.flags & MONO_DATA)) {
          *byteptr++ = temp = log2s (wps->w.slow_level [1]);
          *byteptr++ = temp >> 8;
      }
    }

    *byteptr++ = temp = wps->w.bitrate_acc [0] >> 16;
    *byteptr++ = temp >> 8;

    if (!(wps->wphdr.flags & MONO_DATA)) {
      *byteptr++ = temp = wps->w.bitrate_acc [1] >> 16;
      *byteptr++ = temp >> 8;
    }

    if (wps->w.bitrate_delta [0] | wps->w.bitrate_delta [1]) {
      *byteptr++ = temp = log2s (wps->w.bitrate_delta [0]);
      *byteptr++ = temp >> 8;

      if (!(wps->wphdr.flags & MONO_DATA)) {
          *byteptr++ = temp = log2s (wps->w.bitrate_delta [1]);
          *byteptr++ = temp >> 8;
      }
    }

    wpmd->byte_length = (int32_t)(byteptr - (uchar *) wpmd->data);
    read_hybrid_profile (wps, wpmd);
}

#endif

// Read the median log2 values from the specifed metadata structure, convert
// them back to 32-bit unsigned values and store them. If length is not
// exactly correct then we flag and return an error.

int read_entropy_vars (WavpackStream *wps, WavpackMetadata *wpmd)
{
    uchar *byteptr = wpmd->data;

    if (wpmd->byte_length != ((wps->wphdr.flags & MONO_DATA) ? 6 : 12))
      return FALSE;

    wps->w.median [0] [0] = exp2s (byteptr [0] + (byteptr [1] << 8));
    wps->w.median [1] [0] = exp2s (byteptr [2] + (byteptr [3] << 8));
    wps->w.median [2] [0] = exp2s (byteptr [4] + (byteptr [5] << 8));

    if (!(wps->wphdr.flags & MONO_DATA)) {
      wps->w.median [0] [1] = exp2s (byteptr [6] + (byteptr [7] << 8));
      wps->w.median [1] [1] = exp2s (byteptr [8] + (byteptr [9] << 8));
      wps->w.median [2] [1] = exp2s (byteptr [10] + (byteptr [11] << 8));
    }

    return TRUE;
}

// Read the hybrid related values from the specifed metadata structure, convert
// them back to their internal formats and store them. The extended profile
// stuff is not implemented yet, so return an error if we get more data than
// we know what to do with.

int read_hybrid_profile (WavpackStream *wps, WavpackMetadata *wpmd)
{
    uchar *byteptr = wpmd->data;
    uchar *endptr = byteptr + wpmd->byte_length;

    if (wps->wphdr.flags & HYBRID_BITRATE) {
      wps->w.slow_level [0] = exp2s (byteptr [0] + (byteptr [1] << 8));
      byteptr += 2;

      if (!(wps->wphdr.flags & MONO_DATA)) {
          wps->w.slow_level [1] = exp2s (byteptr [0] + (byteptr [1] << 8));
          byteptr += 2;
      }
    }

    wps->w.bitrate_acc [0] = (int32_t)(byteptr [0] + (byteptr [1] << 8)) << 16;
    byteptr += 2;

    if (!(wps->wphdr.flags & MONO_DATA)) {
      wps->w.bitrate_acc [1] = (int32_t)(byteptr [0] + (byteptr [1] << 8)) << 16;
      byteptr += 2;
    }

    if (byteptr < endptr) {
      wps->w.bitrate_delta [0] = exp2s ((short)(byteptr [0] + (byteptr [1] << 8)));
      byteptr += 2;

      if (!(wps->wphdr.flags & MONO_DATA)) {
          wps->w.bitrate_delta [1] = exp2s ((short)(byteptr [0] + (byteptr [1] << 8)));
          byteptr += 2;
      }

      if (byteptr < endptr)
          return FALSE;
    }
    else
      wps->w.bitrate_delta [0] = wps->w.bitrate_delta [1] = 0;

    return TRUE;
}

// This function is called during both encoding and decoding of hybrid data to
// update the "error_limit" variable which determines the maximum sample error
// allowed in the main bitstream. In the HYBRID_BITRATE mode (which is the only
// currently implemented) this is calculated from the slow_level values and the
// bitrate accumulators. Note that the bitrate accumulators can be changing.

static void update_error_limit (WavpackStream *wps)
{
    int bitrate_0 = (wps->w.bitrate_acc [0] += wps->w.bitrate_delta [0]) >> 16;

    if (wps->wphdr.flags & MONO_DATA) {
      if (wps->wphdr.flags & HYBRID_BITRATE) {
          int slow_log_0 = (wps->w.slow_level [0] + SLO) >> SLS;

          if (slow_log_0 - bitrate_0 > -0x100)
            wps->w.error_limit [0] = exp2s (slow_log_0 - bitrate_0 + 0x100);
          else
            wps->w.error_limit [0] = 0;
      }
      else
          wps->w.error_limit [0] = exp2s (bitrate_0);
    }
    else {
      int bitrate_1 = (wps->w.bitrate_acc [1] += wps->w.bitrate_delta [1]) >> 16;

      if (wps->wphdr.flags & HYBRID_BITRATE) {
          int slow_log_0 = (wps->w.slow_level [0] + SLO) >> SLS;
          int slow_log_1 = (wps->w.slow_level [1] + SLO) >> SLS;

          if (wps->wphdr.flags & HYBRID_BALANCE) {
            int balance = (slow_log_1 - slow_log_0 + bitrate_1 + 1) >> 1;

            if (balance > bitrate_0) {
                bitrate_1 = bitrate_0 * 2;
                bitrate_0 = 0;
            }
            else if (-balance > bitrate_0) {
                bitrate_0 = bitrate_0 * 2;
                bitrate_1 = 0;
            }
            else {
                bitrate_1 = bitrate_0 + balance;
                bitrate_0 = bitrate_0 - balance;
            }
          }

          if (slow_log_0 - bitrate_0 > -0x100)
            wps->w.error_limit [0] = exp2s (slow_log_0 - bitrate_0 + 0x100);
          else
            wps->w.error_limit [0] = 0;

          if (slow_log_1 - bitrate_1 > -0x100)
            wps->w.error_limit [1] = exp2s (slow_log_1 - bitrate_1 + 0x100);
          else
            wps->w.error_limit [1] = 0;
      }
      else {
          wps->w.error_limit [0] = exp2s (bitrate_0);
          wps->w.error_limit [1] = exp2s (bitrate_1);
      }
    }
}

#ifndef NO_PACK

// This function writes the specified word to the open bitstream "wvbits" and,
// if the bitstream "wvcbits" is open, writes any correction data there. This
// function will work for either lossless or hybrid but because a version
// optimized for lossless exits below, it would normally be used for the hybrid
// mode only. The return value is the actual value stored to the stream (even
// if a correction file is being created) and is used as feedback to the
// predictor.

int32_t FASTCALL send_word (WavpackStream *wps, int32_t value, int chan)
{
    uint32_t ones_count, low, mid, high;
    int sign = (value < 0) ? 1 : 0;

#ifdef DEBUG_WORDS
    mid = value;
    ones_count = 32;
    while (ones_count--) {
      putbit (value & 1, &wps->wvbits);
      value >>= 1;
    }
    return mid;
#endif

    if (!(wps->w.median [0] [0] & ~1) && !wps->w.holding_zero && !(wps->w.median [0] [1] & ~1)) {
      if (wps->w.zeros_acc) {
          if (value)
            flush_word (wps);
          else {
            wps->w.slow_level [chan] -= (wps->w.slow_level [chan] + SLO) >> SLS;
            wps->w.zeros_acc++;
            return 0;
          }
      }
      else if (value) {
          putbit_0 (&wps->wvbits);
      }
      else {
          wps->w.slow_level [chan] -= (wps->w.slow_level [chan] + SLO) >> SLS;
          CLEAR (wps->w.median);
          wps->w.zeros_acc = 1;
          return 0;
      }
    }

    if (sign)
      value = ~value;

    if ((wps->wphdr.flags & HYBRID_FLAG) && !chan)
      update_error_limit (wps);

    if (value < (int32_t) GET_MED (0)) {
      ones_count = low = 0;
      high = GET_MED (0) - 1;
      DEC_MED0 ();
    }
    else {
      low = GET_MED (0);
      INC_MED0 ();

      if (value - low < GET_MED (1)) {
          ones_count = 1;
          high = low + GET_MED (1) - 1;
          DEC_MED1 ();
      }
      else {
          low += GET_MED (1);
          INC_MED1 ();

          if (value - low < GET_MED (2)) {
            ones_count = 2;
            high = low + GET_MED (2) - 1;
            DEC_MED2 ();
          }
          else {
            ones_count = 2 + (value - low) / GET_MED (2);
            low += (ones_count - 2) * GET_MED (2);
            high = low + GET_MED (2) - 1;
            INC_MED2 ();
          }
      }
    }

    mid = (high + low + 1) >> 1;

    if (wps->w.holding_zero) {
      if (ones_count)
          wps->w.holding_one++;

      flush_word (wps);

      if (ones_count) {
          wps->w.holding_zero = 1;
          ones_count--;
      }
      else
          wps->w.holding_zero = 0;
    }
    else
      wps->w.holding_zero = 1;

    wps->w.holding_one = ones_count * 2;

    if (!wps->w.error_limit [chan]) {
      if (high != low) {      
          uint32_t maxcode = high - low, code = value - low;
          int bitcount = count_bits (maxcode);
          uint32_t extras = bitset [bitcount] - maxcode - 1;

          if (code < extras) {
            wps->w.pend_data |= code << wps->w.pend_count;
            wps->w.pend_count += bitcount - 1;
          }
          else {
            wps->w.pend_data |= ((code + extras) >> 1) << wps->w.pend_count;
            wps->w.pend_count += bitcount - 1;
            wps->w.pend_data |= ((code + extras) & 1) << wps->w.pend_count++;
          }
      }

      mid = value;
    }
    else
      while (high - low > wps->w.error_limit [chan])
          if (value < (int32_t) mid) {
            mid = ((high = mid - 1) + low + 1) >> 1;
            wps->w.pend_count++;
          }
          else {
            mid = (high + (low = mid) + 1) >> 1;
            wps->w.pend_data |= bitset [wps->w.pend_count++];
          }

    wps->w.pend_data |= ((int32_t) sign << wps->w.pend_count++);

    if (!wps->w.holding_zero)
      flush_word (wps);

    if (bs_is_open (&wps->wvcbits) && wps->w.error_limit [chan]) {
      uint32_t code = value - low, maxcode = high - low;
      int bitcount = count_bits (maxcode);
      uint32_t extras = bitset [bitcount] - maxcode - 1;

      if (bitcount) {
          if (code < extras) {
            putbits (code, bitcount - 1, &wps->wvcbits);
          }
          else {
            putbits ((code + extras) >> 1, bitcount - 1, &wps->wvcbits);
            putbit ((code + extras) & 1, &wps->wvcbits);
          }
      }
    }

    if (wps->wphdr.flags & HYBRID_BITRATE) {
      wps->w.slow_level [chan] -= (wps->w.slow_level [chan] + SLO) >> SLS;
      wps->w.slow_level [chan] += mylog2 (mid);
    }

    return sign ? ~mid : mid;
}

// This function is an optimized version of send_word() that only handles
// lossless (error_limit == 0). It does not return a value because it always
// encodes the exact value passed.

void FASTCALL send_word_lossless (WavpackStream *wps, int32_t value, int chan)
{
    int sign = (value < 0) ? 1 : 0;
    uint32_t ones_count, low, high;

#ifdef DEBUG_WORDS
    ones_count = 32;
    while (ones_count--) {
      putbit (value & 1, &wps->wvbits);
      value >>= 1;
    }
    return;
#endif

    if (!(wps->w.median [0] [0] & ~1) && !wps->w.holding_zero && !(wps->w.median [0] [1] & ~1)) {
      if (wps->w.zeros_acc) {
          if (value)
            flush_word (wps);
          else {
            wps->w.zeros_acc++;
            return;
          }
      }
      else if (value) {
          putbit_0 (&wps->wvbits);
      }
      else {
          CLEAR (wps->w.median);
          wps->w.zeros_acc = 1;
          return;
      }
    }

    if (sign)
      value = ~value;

    if (value < (int32_t) GET_MED (0)) {
      ones_count = low = 0;
      high = GET_MED (0) - 1;
      DEC_MED0 ();
    }
    else {
      low = GET_MED (0);
      INC_MED0 ();

      if (value - low < GET_MED (1)) {
          ones_count = 1;
          high = low + GET_MED (1) - 1;
          DEC_MED1 ();
      }
      else {
          low += GET_MED (1);
          INC_MED1 ();

          if (value - low < GET_MED (2)) {
            ones_count = 2;
            high = low + GET_MED (2) - 1;
            DEC_MED2 ();
          }
          else {
            ones_count = 2 + (value - low) / GET_MED (2);
            low += (ones_count - 2) * GET_MED (2);
            high = low + GET_MED (2) - 1;
            INC_MED2 ();
          }
      }
    }

    if (wps->w.holding_zero) {
      if (ones_count)
          wps->w.holding_one++;

      flush_word (wps);

      if (ones_count) {
          wps->w.holding_zero = 1;
          ones_count--;
      }
      else
          wps->w.holding_zero = 0;
    }
    else
      wps->w.holding_zero = 1;

    wps->w.holding_one = ones_count * 2;

    if (high != low) {  
      uint32_t maxcode = high - low, code = value - low;
      int bitcount = count_bits (maxcode);
      uint32_t extras = bitset [bitcount] - maxcode - 1;

      if (code < extras) {
          wps->w.pend_data |= code << wps->w.pend_count;
          wps->w.pend_count += bitcount - 1;
      }
      else {
          wps->w.pend_data |= ((code + extras) >> 1) << wps->w.pend_count;
          wps->w.pend_count += bitcount - 1;
          wps->w.pend_data |= ((code + extras) & 1) << wps->w.pend_count++;
      }
    }

    wps->w.pend_data |= ((int32_t) sign << wps->w.pend_count++);

    if (!wps->w.holding_zero)
      flush_word (wps);
}

// Used by send_word() and send_word_lossless() to actually send most the
// accumulated data onto the bitstream. This is also called directly from
// clients when all words have been sent.

void flush_word (WavpackStream *wps)
{
    if (wps->w.zeros_acc) {
      int cbits = count_bits (wps->w.zeros_acc);

      while (cbits--) {
          putbit_1 (&wps->wvbits);
      }

      putbit_0 (&wps->wvbits);

      while (wps->w.zeros_acc > 1) {
          putbit (wps->w.zeros_acc & 1, &wps->wvbits);
          wps->w.zeros_acc >>= 1;
      }

      wps->w.zeros_acc = 0;
    }

    if (wps->w.holding_one) {
#ifdef LIMIT_ONES
      if (wps->w.holding_one >= LIMIT_ONES) {
          int cbits;

          putbits ((1L << LIMIT_ONES) - 1, LIMIT_ONES + 1, &wps->wvbits);
          wps->w.holding_one -= LIMIT_ONES;
          cbits = count_bits (wps->w.holding_one);

          while (cbits--) {
            putbit_1 (&wps->wvbits);
          }

          putbit_0 (&wps->wvbits);

          while (wps->w.holding_one > 1) {
            putbit (wps->w.holding_one & 1, &wps->wvbits);
            wps->w.holding_one >>= 1;
          }

          wps->w.holding_zero = 0;
      }
      else
          putbits (bitmask [wps->w.holding_one], wps->w.holding_one, &wps->wvbits);

      wps->w.holding_one = 0;
#else
      do {
          putbit_1 (&wps->wvbits);
      } while (--wps->w.holding_one);
#endif
    }

    if (wps->w.holding_zero) {
      putbit_0 (&wps->wvbits);
      wps->w.holding_zero = 0;
    }

    if (wps->w.pend_count) {
      putbits (wps->w.pend_data, wps->w.pend_count, &wps->wvbits);
      wps->w.pend_data = wps->w.pend_count = 0;
    }
}

// This function is similar to send_word() except that no data is actually
// written to any stream, but it does return the value that would have been
// sent to a hybrid stream. It is used to determine beforehand how much noise
// will be added to samples.

int32_t nosend_word (WavpackStream *wps, int32_t value, int chan)
{
    uint32_t ones_count, low, mid, high;
    int sign = (value < 0) ? 1 : 0;

    if (sign)
      value = ~value;

    if ((wps->wphdr.flags & HYBRID_FLAG) && !chan)
      update_error_limit (wps);

    if (value < (int32_t) GET_MED (0)) {
      low = 0;
      high = GET_MED (0) - 1;
      DEC_MED0 ();
    }
    else {
      low = GET_MED (0);
      INC_MED0 ();

      if (value - low < GET_MED (1)) {
          high = low + GET_MED (1) - 1;
          DEC_MED1 ();
      }
      else {
          low += GET_MED (1);
          INC_MED1 ();

          if (value - low < GET_MED (2)) {
            high = low + GET_MED (2) - 1;
            DEC_MED2 ();
          }
          else {
            ones_count = 2 + (value - low) / GET_MED (2);
            low += (ones_count - 2) * GET_MED (2);
            high = low + GET_MED (2) - 1;
            INC_MED2 ();
          }
      }
    }

    mid = (high + low + 1) >> 1;

    if (!wps->w.error_limit [chan])
      mid = value;
    else
      while (high - low > wps->w.error_limit [chan])
          if (value < (int32_t) mid)
            mid = ((high = mid - 1) + low + 1) >> 1;
          else
            mid = (high + (low = mid) + 1) >> 1;

    wps->w.slow_level [chan] -= (wps->w.slow_level [chan] + SLO) >> SLS;
    wps->w.slow_level [chan] += mylog2 (mid);

    return sign ? ~mid : mid;
}

// This function is used to scan some number of samples to set the variables
// "slow_level" and the "median" array. In pure symetrical encoding mode this
// would not be needed because these values would simply be continued from the
// previous block. However, in the -X modes and the 32-bit modes we cannot do
// this because parameters may change between blocks and the variables might
// not apply. This function can work in mono or stereo and can scan a block
// in either direction.

void scan_word (WavpackStream *wps, int32_t *samples, uint32_t num_samples, int dir)
{
    uint32_t flags = wps->wphdr.flags, value, low;
    int chan;

    init_words (wps);

    if (flags & MONO_DATA) {
      if (dir < 0) {
          samples += (num_samples - 1);
          dir = -1;
      }
      else
          dir = 1;
    }
    else {
      if (dir < 0) {
          samples += (num_samples - 1) * 2;
          dir = -2;
      }
      else
          dir = 2;
    }

    while (num_samples--) {

      value = labs (samples [chan = 0]);

      if (flags & HYBRID_BITRATE) {
          wps->w.slow_level [0] -= (wps->w.slow_level [0] + SLO) >> SLS;
          wps->w.slow_level [0] += mylog2 (value);
      }

      if (value < GET_MED (0)) {
          DEC_MED0 ();
      }
      else {
          low = GET_MED (0);
          INC_MED0 ();

          if (value - low < GET_MED (1)) {
            DEC_MED1 ();
          }
          else {
            low += GET_MED (1);
            INC_MED1 ();

            if (value - low < GET_MED (2)) {
                DEC_MED2 ();
            }
            else {
                INC_MED2 ();
            }
          }
      }

      if (!(flags & MONO_DATA)) {
          value = labs (samples [chan = 1]);

          if (wps->wphdr.flags & HYBRID_BITRATE) {
            wps->w.slow_level [1] -= (wps->w.slow_level [1] + SLO) >> SLS;
            wps->w.slow_level [1] += mylog2 (value);
          }

          if (value < GET_MED (0)) {
            DEC_MED0 ();
          }
          else {
            low = GET_MED (0);
            INC_MED0 ();

            if (value - low < GET_MED (1)) {
                DEC_MED1 ();
            }
            else {
                low += GET_MED (1);
                INC_MED1 ();

                if (value - low < GET_MED (2)) {
                  DEC_MED2 ();
                }
                else {
                  INC_MED2 ();
                }
            }
          }
      }

      samples += dir;
    }
}

#endif

#ifndef NO_UNPACK

static uint32_t FASTCALL read_code (Bitstream *bs, uint32_t maxcode);

// Read the next word from the bitstream "wvbits" and return the value. This
// function can be used for hybrid or lossless streams, but since an
// optimized version is available for lossless this function would normally
// be used for hybrid only. If a hybrid lossless stream is being read then
// the "correction" offset is written at the specified pointer. A return value
// of WORD_EOF indicates that the end of the bitstream was reached (all 1s) or
// some other error occurred.

int32_t FASTCALL get_word (WavpackStream *wps, int chan, int32_t *correction)
{
    uint32_t ones_count, low, mid, high;
    int next8, sign;
    int32_t value;

    if (correction)
      *correction = 0;

#ifdef DEBUG_WORDS
    ones_count = 32;
    while (ones_count--)
      value = getbit (&wps->wvbits) ? (value >> 1) | 0x80000000 : (value >> 1) & 0x7fffffff;
    return value;
#endif

    if (!(wps->w.median [0] [0] & ~1) && !wps->w.holding_zero && !wps->w.holding_one && !(wps->w.median [0] [1] & ~1)) {
      uint32_t mask;
      int cbits;

      if (wps->w.zeros_acc) {
          if (--wps->w.zeros_acc) {
            wps->w.slow_level [chan] -= (wps->w.slow_level [chan] + SLO) >> SLS;
            return 0;
          }
      }
      else {
          for (cbits = 0; cbits < 33 && getbit (&wps->wvbits); ++cbits);

          if (cbits == 33)
            return WORD_EOF;

          if (cbits < 2)
            wps->w.zeros_acc = cbits;
          else {
            for (mask = 1, wps->w.zeros_acc = 0; --cbits; mask <<= 1)
                if (getbit (&wps->wvbits))
                  wps->w.zeros_acc |= mask;

            wps->w.zeros_acc |= mask;
          }

          if (wps->w.zeros_acc) {
            wps->w.slow_level [chan] -= (wps->w.slow_level [chan] + SLO) >> SLS;
            CLEAR (wps->w.median);
            return 0;
          }
      }
    }

    if (wps->w.holding_zero)
      ones_count = wps->w.holding_zero = 0;
    else {
      if (wps->wvbits.bc < 8) {
          if (++(wps->wvbits.ptr) == wps->wvbits.end)
            wps->wvbits.wrap (&wps->wvbits);

          next8 = (wps->wvbits.sr |= *(wps->wvbits.ptr) << wps->wvbits.bc) & 0xff;
          wps->wvbits.bc += 8;
      }
      else
          next8 = wps->wvbits.sr & 0xff;

      if (next8 == 0xff) {
          wps->wvbits.bc -= 8;
          wps->wvbits.sr >>= 8;

          for (ones_count = 8; ones_count < (LIMIT_ONES + 1) && getbit (&wps->wvbits); ++ones_count);

          if (ones_count == (LIMIT_ONES + 1))
            return WORD_EOF;

          if (ones_count == LIMIT_ONES) {
            uint32_t mask;
            int cbits;

            for (cbits = 0; cbits < 33 && getbit (&wps->wvbits); ++cbits);

            if (cbits == 33)
                return WORD_EOF;

            if (cbits < 2)
                ones_count = cbits;
            else {
                for (mask = 1, ones_count = 0; --cbits; mask <<= 1)
                  if (getbit (&wps->wvbits))
                      ones_count |= mask;

                ones_count |= mask;
            }

            ones_count += LIMIT_ONES;
          }
      }
      else {
          wps->wvbits.bc -= (ones_count = ones_count_table [next8]) + 1;
          wps->wvbits.sr >>= ones_count + 1;
      }

      if (wps->w.holding_one) {
          wps->w.holding_one = ones_count & 1;
          ones_count = (ones_count >> 1) + 1;
      }
      else {
          wps->w.holding_one = ones_count & 1;
          ones_count >>= 1;
      }

      wps->w.holding_zero = ~wps->w.holding_one & 1;
    }

    if ((wps->wphdr.flags & HYBRID_FLAG) && !chan)
      update_error_limit (wps);

    if (ones_count == 0) {
      low = 0;
      high = GET_MED (0) - 1;
      DEC_MED0 ();
    }
    else {
      low = GET_MED (0);
      INC_MED0 ();

      if (ones_count == 1) {
          high = low + GET_MED (1) - 1;
          DEC_MED1 ();
      }
      else {
          low += GET_MED (1);
          INC_MED1 ();

          if (ones_count == 2) {
            high = low + GET_MED (2) - 1;
            DEC_MED2 ();
          }
          else {
            low += (ones_count - 2) * GET_MED (2);
            high = low + GET_MED (2) - 1;
            INC_MED2 ();
          }
      }
    }

    mid = (high + low + 1) >> 1;

    if (!wps->w.error_limit [chan])
      mid = read_code (&wps->wvbits, high - low) + low;
    else while (high - low > wps->w.error_limit [chan]) {
      if (getbit (&wps->wvbits))
          mid = (high + (low = mid) + 1) >> 1;
      else
          mid = ((high = mid - 1) + low + 1) >> 1;
    }

    sign = getbit (&wps->wvbits);

    if (bs_is_open (&wps->wvcbits) && wps->w.error_limit [chan]) {
      value = read_code (&wps->wvcbits, high - low) + low;

      if (correction)
          *correction = sign ? (mid - value) : (value - mid);
    }

    if (wps->wphdr.flags & HYBRID_BITRATE) {
      wps->w.slow_level [chan] -= (wps->w.slow_level [chan] + SLO) >> SLS;
      wps->w.slow_level [chan] += mylog2 (mid);
    }

    return sign ? ~mid : mid;
}

// This is an optimized version of get_word() that is used for lossless only
// (error_limit == 0). There are two versions of an internal section; they
// are identical from a functional standpoint, but one may be faster than the
// other under different compilers / processors.

int32_t FASTCALL get_word_lossless (WavpackStream *wps, int chan)
{
    uint32_t ones_count, low, high;
    int next8;

#ifdef DEBUG_WORDS
    ones_count = 32;
    while (ones_count--)
      low = getbit (&wps->wvbits) ? (low >> 1) | 0x80000000 : (low >> 1) & 0x7fffffff;
    return low;
#endif

    if (!(wps->w.median [0] [0] & ~1) && !wps->w.holding_zero && !wps->w.holding_one && !(wps->w.median [0] [1] & ~1)) {
      uint32_t mask;
      int cbits;

      if (wps->w.zeros_acc) {
          if (--wps->w.zeros_acc)
            return 0;
      }
      else {
          for (cbits = 0; cbits < 33 && getbit (&wps->wvbits); ++cbits);

          if (cbits == 33)
            return WORD_EOF;

          if (cbits < 2)
            wps->w.zeros_acc = cbits;
          else {
            for (mask = 1, wps->w.zeros_acc = 0; --cbits; mask <<= 1)
                if (getbit (&wps->wvbits))
                  wps->w.zeros_acc |= mask;

            wps->w.zeros_acc |= mask;
          }

          if (wps->w.zeros_acc) {
            CLEAR (wps->w.median);
            return 0;
          }
      }
    }

    if (wps->w.holding_zero)
      ones_count = wps->w.holding_zero = 0;
    else {
      if (wps->wvbits.bc < 8) {
          if (++(wps->wvbits.ptr) == wps->wvbits.end)
            wps->wvbits.wrap (&wps->wvbits);

          next8 = (wps->wvbits.sr |= *(wps->wvbits.ptr) << wps->wvbits.bc) & 0xff;
          wps->wvbits.bc += 8;
      }
      else
          next8 = wps->wvbits.sr & 0xff;

      if (next8 == 0xff) {
          wps->wvbits.bc -= 8;
          wps->wvbits.sr >>= 8;

          for (ones_count = 8; ones_count < (LIMIT_ONES + 1) && getbit (&wps->wvbits); ++ones_count);

          if (ones_count == (LIMIT_ONES + 1))
            return WORD_EOF;

          if (ones_count == LIMIT_ONES) {
            uint32_t mask;
            int cbits;

            for (cbits = 0; cbits < 33 && getbit (&wps->wvbits); ++cbits);

            if (cbits == 33)
                return WORD_EOF;

            if (cbits < 2)
                ones_count = cbits;
            else {
                for (mask = 1, ones_count = 0; --cbits; mask <<= 1)
                  if (getbit (&wps->wvbits))
                      ones_count |= mask;

                ones_count |= mask;
            }

            ones_count += LIMIT_ONES;
          }
      }
      else {
          wps->wvbits.bc -= (ones_count = ones_count_table [next8]) + 1;
          wps->wvbits.sr >>= ones_count + 1;
      }

      if (wps->w.holding_one) {
          wps->w.holding_one = ones_count & 1;
          ones_count = (ones_count >> 1) + 1;
      }
      else {
          wps->w.holding_one = ones_count & 1;
          ones_count >>= 1;
      }

      wps->w.holding_zero = ~wps->w.holding_one & 1;
    }

    if (ones_count == 0) {
      low = 0;
      high = GET_MED (0) - 1;
      DEC_MED0 ();
    }
    else {
      low = GET_MED (0);
      INC_MED0 ();

      if (ones_count == 1) {
          high = low + GET_MED (1) - 1;
          DEC_MED1 ();
      }
      else {
          low += GET_MED (1);
          INC_MED1 ();

          if (ones_count == 2) {
            high = low + GET_MED (2) - 1;
            DEC_MED2 ();
          }
          else {
            low += (ones_count - 2) * GET_MED (2);
            high = low + GET_MED (2) - 1;
            INC_MED2 ();
          }
      }
    }

    low += read_code (&wps->wvbits, high - low);
    return (getbit (&wps->wvbits)) ? ~low : low;
}

// Read a single unsigned value from the specified bitstream with a value
// from 0 to maxcode. If there are exactly a power of two number of possible
// codes then this will read a fixed number of bits; otherwise it reads the
// minimum number of bits and then determines whether another bit is needed
// to define the code.

static uint32_t FASTCALL read_code (Bitstream *bs, uint32_t maxcode)
{
    int bitcount = count_bits (maxcode);
    uint32_t extras = bitset [bitcount] - maxcode - 1, code;

    if (!bitcount)
      return 0;

    getbits (&code, bitcount - 1, bs);
    code &= bitmask [bitcount - 1];

    if (code >= extras) {
      code = (code << 1) - extras;

      if (getbit (bs))
          ++code;
    }

    return code;
}

#endif

// The concept of a base 2 logarithm is used in many parts of WavPack. It is
// a way of sufficiently accurately representing 32-bit signed and unsigned
// values storing only 16 bits (actually fewer). It is also used in the hybrid
// mode for quickly comparing the relative magnitude of large values (i.e.
// division) and providing smooth exponentials using only addition.

// These are not strict logarithms in that they become linear around zero and
// can therefore represent both zero and negative values. They have 8 bits
// of precision and in "roundtrip" conversions the total error never exceeds 1
// part in 225 except for the cases of +/-115 and +/-195 (which error by 1).


// This function returns the log2 for the specified 32-bit unsigned value.
// The maximum value allowed is about 0xff800000 and returns 8447.

static int FASTCALL mylog2 (uint32_t avalue)
{
    int dbits;

    if ((avalue += avalue >> 9) < (1 << 8)) {
      dbits = nbits_table [avalue];
      return (dbits << 8) + log2_table [(avalue << (9 - dbits)) & 0xff];
    }
    else {
      if (avalue < (1L << 16))
          dbits = nbits_table [avalue >> 8] + 8;
      else if (avalue < (1L << 24))
          dbits = nbits_table [avalue >> 16] + 16;
      else
          dbits = nbits_table [avalue >> 24] + 24;

      return (dbits << 8) + log2_table [(avalue >> (dbits - 9)) & 0xff];
    }
}

// This function scans a buffer of longs and accumulates the total log2 value
// of all the samples. This is useful for determining maximum compression
// because the bitstream storage required for entropy coding is proportional
// to the base 2 log of the samples.

uint32_t log2buffer (int32_t *samples, uint32_t num_samples, int limit)
{
    uint32_t result = 0, avalue;
    int dbits;

    while (num_samples--) {
      avalue = abs (*samples++);

      if ((avalue += avalue >> 9) < (1 << 8)) {
          dbits = nbits_table [avalue];
          result += (dbits << 8) + log2_table [(avalue << (9 - dbits)) & 0xff];
      }
      else {
          if (avalue < (1L << 16))
            dbits = nbits_table [avalue >> 8] + 8;
          else if (avalue < (1L << 24))
            dbits = nbits_table [avalue >> 16] + 16;
          else
            dbits = nbits_table [avalue >> 24] + 24;

          result += dbits = (dbits << 8) + log2_table [(avalue >> (dbits - 9)) & 0xff];

          if (limit && dbits >= limit)
            return (uint32_t) -1;
      }
    }

    return result;
}

// This function returns the log2 for the specified 32-bit signed value.
// All input values are valid and the return values are in the range of
// +/- 8192.

int log2s (int32_t value)
{
    return (value < 0) ? -mylog2 (-value) : mylog2 (value);
}

// This function returns the original integer represented by the supplied
// logarithm (at least within the provided accuracy). The log is signed,
// but since a full 32-bit value is returned this can be used for unsigned
// conversions as well (i.e. the input range is -8192 to +8447).

int32_t exp2s (int log)
{
    uint32_t value;

    if (log < 0)
      return -exp2s (-log);

    value = exp2_table [log & 0xff] | 0x100;

    if ((log >>= 8) <= 9)
      return value >> (9 - log);
    else
      return value << (log - 9);
}

// These two functions convert internal weights (which are normally +/-1024)
// to and from an 8-bit signed character version for storage in metadata. The
// weights are clipped here in the case that they are outside that range.

signed char store_weight (int weight)
{
    if (weight > 1024)
      weight = 1024;
    else if (weight < -1024)
      weight = -1024;

    if (weight > 0)
      weight -= (weight + 64) >> 7;

    return (weight + 4) >> 3;
}

int restore_weight (signed char weight)
{
    int result;

    if ((result = (int) weight << 3) > 0)
      result += (result + 64) >> 7;

    return result;
}

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