ref: b691654525bcadb8474734fd421943a8708d4c84
dir: /common/libsndfile/src/wav_ms_adpcm.c/
/*
** Copyright (C) 1999-2000 Erik de Castro Lopo <erikd@zip.com.au>
**
** This program 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.
**
** This program 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 this program; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <math.h>
#include "sndfile.h"
#include "config.h"
#include "sfendian.h"
#include "common.h"
#include "wav.h"
typedef struct
{ unsigned int channels, blocksize, samplesperblock, blocks, dataremaining ;
int blockcount, samplecount ;
unsigned char *block ;
short *samples ;
unsigned char dummydata [4] ; /* Dummy size */
} MSADPCM_PRIVATE ;
/*============================================================================================
** MS ADPCM static data and functions.
*/
static int AdaptationTable [] =
{ 230, 230, 230, 230, 307, 409, 512, 614,
768, 614, 512, 409, 307, 230, 230, 230
} ;
/* TODO : The first 7 coef's are are always hardcode and must
appear in the actual WAVE file. They should be read in
in case a sound program added extras to the list. */
static int AdaptCoeff1 [] =
{ 256, 512, 0, 192, 240, 460, 392
} ;
static int AdaptCoeff2 [] =
{ 0, -256, 0, 64, 0, -208, -232
} ;
/*============================================================================================
** MS ADPCM Block Layout.
** ======================
** Block is usually 256, 512 or 1024 bytes depending on sample rate.
** For a mono file, the block is laid out as follows:
** byte purpose
** 0 block predictor [0..6]
** 1,2 initial idelta (positive)
** 3,4 sample 1
** 5,6 sample 0
** 7..n packed bytecodes
**
** For a stereo file, the block is laid out as follows:
** byte purpose
** 0 block predictor [0..6] for left channel
** 1 block predictor [0..6] for right channel
** 2,3 initial idelta (positive) for left channel
** 4,5 initial idelta (positive) for right channel
** 6,7 sample 1 for left channel
** 8,9 sample 1 for right channel
** 10,11 sample 0 for left channel
** 12,13 sample 0 for right channel
** 14..n packed bytecodes
*/
/*============================================================================================
** Static functions.
*/
static int msadpcm_read_block (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms) ;
static int msadpcm_read (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms, short *ptr, int len) ;
static int msadpcm_write_block (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms) ;
static int msadpcm_write (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms, short *ptr, int len) ;
static unsigned int srate2blocksize (unsigned int srate) ;
static void choose_predictor (unsigned int channels, short *data, int *bpred, int *idelta) ;
/*============================================================================================
** MS ADPCM Read Functions.
*/
int msadpcm_reader_init (SF_PRIVATE *psf, WAV_FMT *fmt)
{ MSADPCM_PRIVATE *pms ;
unsigned int pmssize ;
int count ;
pmssize = sizeof (MSADPCM_PRIVATE) + fmt->msadpcm.blockalign + 3 * fmt->msadpcm.channels * fmt->msadpcm.samplesperblock ;
if (! (psf->fdata = malloc (pmssize)))
return SFE_MALLOC_FAILED ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
memset (pms, 0, pmssize) ;
pms->block = (unsigned char*) pms->dummydata ;
pms->samples = (short*) (pms->dummydata + fmt->msadpcm.blockalign) ;
pms->channels = fmt->msadpcm.channels ;
pms->blocksize = fmt->msadpcm.blockalign ;
pms->samplesperblock = fmt->msadpcm.samplesperblock ;
pms->dataremaining = psf->datalength ;
if (psf->datalength % pms->blocksize)
pms->blocks = psf->datalength / pms->blocksize + 1 ;
else
pms->blocks = psf->datalength / pms->blocksize ;
count = 2 * (pms->blocksize - 6 * pms->channels) / pms->channels ;
if (pms->samplesperblock != count)
psf_sprintf (psf, "*** Warning : samplesperblock shoud be %d.\n", count) ;
psf->sf.samples = (psf->datalength / pms->blocksize) * pms->samplesperblock ;
psf_sprintf (psf, " bpred idelta\n") ;
msadpcm_read_block (psf, pms) ;
return 0 ;
} /* msadpcm_reader_init */
static
int msadpcm_read_block (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms)
{ int chan, k, blockindex, sampleindex ;
short bytecode, bpred [2], chan_idelta [2] ;
int predict ;
int current ;
int idelta ;
pms->blockcount ++ ;
pms->samplecount = 0 ;
if (pms->blockcount > pms->blocks)
{ memset (pms->samples, 0, pms->samplesperblock * pms->channels) ;
return 1 ;
} ;
if ((k = fread (pms->block, 1, pms->blocksize, psf->file)) != pms->blocksize)
psf_sprintf (psf, "*** Warning : short read (%d != %d).\n", k, pms->blocksize) ;
/* Read and check the block header. */
if (pms->channels == 1)
{ bpred [0] = pms->block [0] ;
if (bpred [0] >= 7)
psf_sprintf (psf, "MS ADPCM synchronisation error (%d).\n", bpred [0]) ;
chan_idelta [0] = pms->block [1] | (pms->block [2] << 8) ;
chan_idelta [1] = 0 ;
psf_sprintf (psf, "(%d) (%d)\n", bpred [0], chan_idelta [0]) ;
pms->samples [1] = pms->block [3] | (pms->block [4] << 8) ;
pms->samples [0] = pms->block [5] | (pms->block [6] << 8) ;
blockindex = 7 ;
}
else
{ bpred [0] = pms->block [0] ;
bpred [1] = pms->block [1] ;
if (bpred [0] >= 7 || bpred [1] >= 7)
psf_sprintf (psf, "MS ADPCM synchronisation error (%d %d).\n", bpred [0], bpred [1]) ;
chan_idelta [0] = pms->block [2] | (pms->block [3] << 8) ;
chan_idelta [1] = pms->block [4] | (pms->block [5] << 8) ;
psf_sprintf (psf, "(%d, %d) (%d, %d)\n", bpred [0], bpred [1], chan_idelta [0], chan_idelta [1]) ;
pms->samples [2] = pms->block [6] | (pms->block [7] << 8) ;
pms->samples [3] = pms->block [8] | (pms->block [9] << 8) ;
pms->samples [0] = pms->block [10] | (pms->block [11] << 8) ;
pms->samples [1] = pms->block [12] | (pms->block [13] << 8) ;
blockindex = 14 ;
} ;
if (chan_idelta [0] & 0x8000)
chan_idelta [0] -= 0x10000 ;
if (chan_idelta [1] & 0x8000)
chan_idelta [1] -= 0x10000 ;
/* Pull apart the packed 4 bit samples and store them in their
** correct sample positions.
*/
sampleindex = 2 * pms->channels ;
while (blockindex < pms->blocksize)
{ bytecode = pms->block [blockindex++] ;
pms->samples [sampleindex++] = (bytecode >> 4) & 0x0F ;
pms->samples [sampleindex++] = bytecode & 0x0F ;
} ;
/* Decode the encoded 4 bit samples. */
for (k = 2 * pms->channels ; k < (pms->samplesperblock * pms->channels) ; k ++)
{ chan = (pms->channels > 1) ? (k % 2) : 0 ;
bytecode = pms->samples [k] & 0xF ;
/** Compute next Adaptive Scale Factor (ASF) **/
idelta = chan_idelta [chan] ;
chan_idelta [chan] = (AdaptationTable [bytecode] * idelta) >> 8 ; /* => / 256 => FIXED_POINT_ADAPTATION_BASE == 256 */
if (chan_idelta [chan] < 16)
chan_idelta [chan] = 16 ;
if (bytecode & 0x8)
bytecode -= 0x10 ;
predict = ((pms->samples [k - pms->channels] * AdaptCoeff1 [bpred [chan]])
+ (pms->samples [k - 2 * pms->channels] * AdaptCoeff2 [bpred [chan]])) >> 8 ; /* => / 256 => FIXED_POINT_COEFF_BASE == 256 */
current = (bytecode * idelta) + predict;
if (current > 32767)
current = 32767 ;
else if (current < -32768)
current = -32768 ;
pms->samples [k] = current ;
} ;
return 1 ;
} /* msadpcm_read_block */
static
int msadpcm_read (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms, short *ptr, int len)
{ int count, total = 0, index = 0 ;
while (index < len)
{ if (pms->blockcount >= pms->blocks && pms->samplecount >= pms->samplesperblock)
{ memset (&(ptr[index]), 0, (len - index) * sizeof (short)) ;
return total ;
} ;
if (pms->samplecount >= pms->samplesperblock)
msadpcm_read_block (psf, pms) ;
count = (pms->samplesperblock - pms->samplecount) * pms->channels ;
count = (len - index > count) ? count : len - index ;
memcpy (&(ptr[index]), &(pms->samples [pms->samplecount * pms->channels]), count * sizeof (short)) ;
index += count ;
pms->samplecount += count / pms->channels ;
total = index ;
} ;
return total ;
} /* msadpcm_read */
int msadpcm_read_s (SF_PRIVATE *psf, short *ptr, int len)
{ MSADPCM_PRIVATE *pms ;
int total ;
if (! psf->fdata)
return 0 ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
total = msadpcm_read (psf, pms, ptr, len) ;
return total ;
} /* msadpcm_read_s */
int msadpcm_read_i (SF_PRIVATE *psf, int *ptr, int len)
{ MSADPCM_PRIVATE *pms ;
short *sptr ;
int k, bufferlen, readcount = 0, count ;
int index = 0, total = 0 ;
if (! psf->fdata)
return 0 ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
sptr = (short*) psf->buffer ;
bufferlen = ((SF_BUFFER_LEN / psf->blockwidth) * psf->blockwidth) / sizeof (short) ;
while (len > 0)
{ readcount = (len >= bufferlen) ? bufferlen : len ;
count = msadpcm_read (psf, pms, sptr, readcount) ;
for (k = 0 ; k < readcount ; k++)
ptr [index+k] = (int) (sptr [k]) ;
index += readcount ;
total += count ;
len -= readcount ;
} ;
return total ;
} /* msadpcm_read_i */
int msadpcm_read_d (SF_PRIVATE *psf, double *ptr, int len, int normalize)
{ MSADPCM_PRIVATE *pms ;
short *sptr ;
int k, bufferlen, readcount = 0, count ;
int index = 0, total = 0 ;
double normfact ;
normfact = (normalize ? 1.0 / ((double) 0x8000) : 1.0) ;
if (! psf->fdata)
return 0 ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
sptr = (short*) psf->buffer ;
bufferlen = ((SF_BUFFER_LEN / psf->blockwidth) * psf->blockwidth) / sizeof (short) ;
while (len > 0)
{ readcount = (len >= bufferlen) ? bufferlen : len ;
count = msadpcm_read (psf, pms, sptr, readcount) ;
for (k = 0 ; k < readcount ; k++)
ptr [index+k] = normfact * (double) (sptr [k]) ;
index += readcount ;
total += count ;
len -= readcount ;
} ;
return total ;
} /* msadpcm_read_d */
off_t msadpcm_seek (SF_PRIVATE *psf, off_t offset, int whence)
{ MSADPCM_PRIVATE *pms ;
int newblock, newsample ;
if (! psf->fdata)
return 0 ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
if (! (psf->blockwidth && psf->datalength && psf->dataoffset))
{ psf->error = SFE_BAD_SEEK ;
return ((off_t) -1) ;
} ;
switch (whence)
{ case SEEK_SET :
if (offset < 0 || offset > pms->blocks * pms->samplesperblock)
{ psf->error = SFE_BAD_SEEK ;
return ((off_t) -1) ;
} ;
newblock = offset / pms->samplesperblock ;
newsample = offset % pms->samplesperblock ;
break ;
case SEEK_CUR :
if (psf->current + offset < 0 || psf->current + offset > pms->blocks * pms->samplesperblock)
{ psf->error = SFE_BAD_SEEK ;
return ((off_t) -1) ;
} ;
newblock = (psf->current + offset) / pms->samplesperblock ;
newsample = (psf->current + offset) % pms->samplesperblock ;
break ;
case SEEK_END :
if (offset > 0 || pms->samplesperblock * pms->blocks + offset < 0)
{ psf->error = SFE_BAD_SEEK ;
return ((off_t) -1) ;
} ;
newblock = (pms->samplesperblock * pms->blocks + offset) / pms->samplesperblock ;
newsample = (pms->samplesperblock * pms->blocks + offset) % pms->samplesperblock ;
break ;
default :
psf->error = SFE_BAD_SEEK ;
return ((off_t) -1) ;
} ;
if (psf->mode == SF_MODE_READ)
{ fseek (psf->file, (int) (psf->dataoffset + newblock * pms->blocksize), SEEK_SET) ;
pms->blockcount = newblock ;
msadpcm_read_block (psf, pms) ;
pms->samplecount = newsample ;
}
else
{ /* What to do about write??? */
psf->error = SFE_BAD_SEEK ;
return ((off_t) -1) ;
} ;
psf->current = newblock * pms->samplesperblock + newsample ;
return psf->current ;
} /* msadpcm_seek */
/*==========================================================================================
** MS ADPCM Write Functions.
*/
int msadpcm_writer_init (SF_PRIVATE *psf, WAV_FMT *fmt)
{ MSADPCM_PRIVATE *pms ;
unsigned int k, pmssize ;
if (fmt->format != 0x0002)
psf_sprintf (psf, "*** Warning : format tag != WAVE_FORMAT_MS_ADPCM.\n") ;
fmt->msadpcm.blockalign = srate2blocksize (fmt->msadpcm.samplerate) ;
fmt->msadpcm.bitwidth = 4 ;
fmt->msadpcm.extrabytes = 32 ;
fmt->msadpcm.samplesperblock = 2 + 2 * (fmt->msadpcm.blockalign - 7 * fmt->msadpcm.channels) / fmt->msadpcm.channels ;
fmt->msadpcm.bytespersec = (fmt->msadpcm.samplerate * fmt->msadpcm.blockalign) / fmt->msadpcm.samplesperblock ;
fmt->msadpcm.numcoeffs = 7 ;
for (k = 0 ; k < 7 ; k++)
{ fmt->msadpcm.coeffs[k].coeff1 = AdaptCoeff1 [k] ;
fmt->msadpcm.coeffs[k].coeff2 = AdaptCoeff2 [k] ;
} ;
pmssize = sizeof (MSADPCM_PRIVATE) + fmt->msadpcm.blockalign + 3 * fmt->msadpcm.channels * fmt->msadpcm.samplesperblock ;
if (! (psf->fdata = malloc (pmssize)))
return SFE_MALLOC_FAILED ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
memset (pms, 0, pmssize) ;
pms->channels = fmt->msadpcm.channels ;
pms->blocksize = fmt->msadpcm.blockalign ;
pms->samplesperblock = fmt->msadpcm.samplesperblock ;
pms->block = (unsigned char*) pms->dummydata ;
pms->samples = (short*) (pms->dummydata + fmt->msadpcm.blockalign) ;
pms->samplecount = 0 ;
return 0 ;
} /* msadpcm_writer_init */
/*==========================================================================================
*/
static
int msadpcm_write_block (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms)
{ unsigned int blockindex ;
unsigned char byte ;
int chan, k, predict, bpred [2], idelta [2], errordelta, newsamp ;
choose_predictor (pms->channels, pms->samples, bpred, idelta) ;
/* Write the block header. */
if (pms->channels == 1)
{ pms->block [0] = bpred [0] ;
pms->block [1] = idelta [0] & 0xFF ;
pms->block [2] = idelta [0] >> 8 ;
pms->block [3] = pms->samples [1] & 0xFF ;
pms->block [4] = pms->samples [1] >> 8 ;
pms->block [5] = pms->samples [0] & 0xFF ;
pms->block [6] = pms->samples [0] >> 8 ;
blockindex = 7 ;
byte = 0 ;
/* Encode the samples as 4 bit. */
for (k = 2 ; k < pms->samplesperblock ; k++)
{ predict = (pms->samples [k-1] * AdaptCoeff1 [bpred [0]] + pms->samples [k-2] * AdaptCoeff2 [bpred [0]]) >> 8 ;
errordelta = (pms->samples [k] - predict) / idelta [0] ;
if (errordelta < -8)
errordelta = -8 ;
else if (errordelta > 7)
errordelta = 7 ;
newsamp = predict + (idelta [0] * errordelta) ;
if (newsamp > 32767)
newsamp = 32767 ;
else if (newsamp < -32768)
newsamp = -32768 ;
if (errordelta < 0)
errordelta += 0x10 ;
byte = (byte << 4) | (errordelta & 0xF) ;
if (k % 2)
{ pms->block [blockindex++] = byte ;
byte = 0 ;
} ;
idelta [0] = (idelta [0] * AdaptationTable [errordelta]) >> 8 ;
if (idelta [0] < 16)
idelta [0] = 16 ;
pms->samples [k] = newsamp ;
} ;
}
else
{ /* Stereo file. */
pms->block [0] = bpred [0] ;
pms->block [1] = bpred [1] ;
pms->block [2] = idelta [0] & 0xFF ;
pms->block [3] = idelta [0] >> 8 ;
pms->block [4] = idelta [1] & 0xFF ;
pms->block [5] = idelta [1] >> 8 ;
pms->block [6] = pms->samples [2] & 0xFF ;
pms->block [7] = pms->samples [2] >> 8 ;
pms->block [8] = pms->samples [3] & 0xFF ;
pms->block [9] = pms->samples [3] >> 8 ;
pms->block [10] = pms->samples [0] & 0xFF ;
pms->block [11] = pms->samples [0] >> 8 ;
pms->block [12] = pms->samples [1] & 0xFF ;
pms->block [13] = pms->samples [1] >> 8 ;
blockindex = 14 ;
byte = 0 ;
chan = 1 ;
for (k = 4 ; k < pms->samplesperblock ; k+=2)
{ chan = chan ? 0 : 1 ;
predict = (pms->samples [k-2] * AdaptCoeff1 [bpred [chan]] + pms->samples [k-4] * AdaptCoeff2 [bpred [chan]]) >> 8 ;
errordelta = (pms->samples [k] - predict) / idelta [chan] ;
if (errordelta < -8)
errordelta = -8 ;
else if (errordelta > 7)
errordelta = 7 ;
newsamp = predict + (idelta [chan] * errordelta) ;
if (newsamp > 32767)
newsamp = 32767 ;
else if (newsamp < -32768)
newsamp = -32768 ;
if (errordelta < 0)
errordelta += 0x10 ;
byte = (byte << 4) | (errordelta & 0xF) ;
if (k % 2)
{ pms->block [blockindex++] = byte ;
byte = 0 ;
} ;
idelta [chan] = (idelta [chan] * AdaptationTable [errordelta]) >> 8 ;
if (idelta [chan] < 16)
idelta [chan] = 16 ;
pms->samples [k-2] = newsamp ;
} ;
} ;
/* Write the block to disk. */
if ((k = fwrite (pms->block, 1, pms->blocksize, psf->file)) != pms->blocksize)
psf_sprintf (psf, "*** Warning : short write (%d != %d).\n", k, pms->blocksize) ;
memset (pms->samples, 0, pms->samplesperblock * sizeof (short)) ;
pms->blockcount ++ ;
pms->samplecount = 0 ;
return 1 ;
} /* msadpcm_write_block */
static
int msadpcm_write (SF_PRIVATE *psf, MSADPCM_PRIVATE *pms, short *ptr, int len)
{ int count, total = 0, index = 0 ;
while (index < len)
{ count = (pms->samplesperblock - pms->samplecount) * pms->channels ;
if (count > len - index)
count = len - index ;
memcpy (&(pms->samples [pms->samplecount * pms->channels]), &(ptr [index]), count * sizeof (short)) ;
index += count ;
pms->samplecount += count / pms->channels ;
total = index ;
if (pms->samplecount >= pms->samplesperblock)
msadpcm_write_block (psf, pms) ;
} ;
return total ;
} /* msadpcm_write */
int msadpcm_write_s (SF_PRIVATE *psf, short *ptr, int len)
{ MSADPCM_PRIVATE *pms ;
int total ;
if (! psf->fdata)
return 0 ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
total = msadpcm_write (psf, pms, ptr, len) ;
return total ;
} /* msadpcm_write_s */
int msadpcm_write_i (SF_PRIVATE *psf, int *ptr, int len)
{ MSADPCM_PRIVATE *pms ;
short *sptr ;
int k, bufferlen, writecount = 0, count ;
int index = 0, total = 0 ;
if (! psf->fdata)
return 0 ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
sptr = (short*) psf->buffer ;
bufferlen = ((SF_BUFFER_LEN / psf->blockwidth) * psf->blockwidth) / sizeof (short) ;
while (len > 0)
{ writecount = (len >= bufferlen) ? bufferlen : len ;
for (k = 0 ; k < writecount ; k++)
sptr [k] = (short) ptr [index+k] ;
count = msadpcm_write (psf, pms, sptr, writecount) ;
index += writecount ;
total += count ;
len -= writecount ;
} ;
return total ;
} /* msadpcm_write_i */
int msadpcm_write_d (SF_PRIVATE *psf, double *ptr, int len, int normalize)
{ MSADPCM_PRIVATE *pms ;
short *sptr ;
int k, bufferlen, writecount = 0, count ;
int index = 0, total = 0 ;
double normfact ;
normfact = (normalize ? ((double) 0x8000) : 1.0) ;
if (! psf->fdata)
return 0 ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
sptr = (short*) psf->buffer ;
bufferlen = ((SF_BUFFER_LEN / psf->blockwidth) * psf->blockwidth) / sizeof (short) ;
while (len > 0)
{ writecount = (len >= bufferlen) ? bufferlen : len ;
for (k = 0 ; k < writecount ; k++)
sptr [k] = (short) (normfact * ptr [index+k]) ;
count = msadpcm_write (psf, pms, sptr, writecount) ;
index += writecount ;
total += count ;
len -= writecount ;
} ;
return total ;
} /* msadpcm_write_d */
/*========================================================================================
*/
int msadpcm_close (SF_PRIVATE *psf)
{ MSADPCM_PRIVATE *pms ;
unsigned int dword ;
if (! psf->fdata)
return wav_close (psf) ;
pms = (MSADPCM_PRIVATE*) psf->fdata ;
if (psf->mode == SF_MODE_WRITE)
{ /* Now we know for certain the length of the file we can
** re-write correct values for the RIFF and data chunks.
*/
if (pms->samplecount && pms->samplecount < pms->samplesperblock)
msadpcm_write_block (psf, pms) ;
fseek (psf->file, 0, SEEK_END) ;
psf->filelength = ftell (psf->file) ;
/* Fix RIFF size. */
dword = H2LE_INT (psf->filelength - 2 * sizeof (dword)) ;
fseek (psf->file, sizeof (dword), SEEK_SET) ;
fwrite (&dword, sizeof (dword), 1, psf->file) ;
psf->datalength = psf->filelength - psf->dataoffset ;
fseek (psf->file, (int) (psf->dataoffset - sizeof (dword)), SEEK_SET) ;
dword = H2LE_INT (psf->datalength) ;
fwrite (&dword, sizeof (dword), 1, psf->file) ;
} ;
if (psf->fdata)
free (psf->fdata) ;
psf->fdata = NULL ;
return 0 ;
} /* msadpcm_close */
/*========================================================================================
** Static functions.
*/
static
unsigned int srate2blocksize (unsigned int srate)
{ if (srate < 12000)
return 256 ;
if (srate < 23000)
return 512 ;
return 1024 ;
} /* srate2blocksize */
/*----------------------------------------------------------------------------------------
** Choosing the block predictor.
** Each block requires a predictor and an idelta for each channel.
** The predictor is in the range [0..6] which is an index into the two AdaptCoeff tables.
** The predictor is chosen by trying all of the possible predictors on a small set of
** samples at the beginning of the block. The predictor with the smallest average
** abs (idelta) is chosen as the best predictor for this block.
** The value of idelta is chosen to to give a 4 bit code value of +/- 4 (approx. half the
** max. code value). If the average abs (idelta) is zero, the sixth predictor is chosen.
** If the value of idelta is less then 16 it is set to 16.
**
** Microsoft uses an IDELTA_COUNT (number of sample pairs used to choose best predictor)
** value of 3. The best possible results would be obtained by using all the samples to
** choose the predictor.
*/
#define IDELTA_COUNT 3
static
void choose_predictor (unsigned int channels, short *data, int *block_pred, int *idelta)
{ unsigned int chan, k, bpred, idelta_sum, best_bpred, best_idelta ;
for (chan = 0 ; chan < channels; chan++)
{ best_bpred = best_idelta = 0 ;
for (bpred = 0 ; bpred < 7 ; bpred++)
{ idelta_sum = 0 ;
for (k = 2 ; k < 2 + IDELTA_COUNT ; k++)
idelta_sum += abs (data [k*channels] - ((data [(k-1)*channels] * AdaptCoeff1 [bpred] + data [(k-2)*channels] * AdaptCoeff2 [bpred]) >> 8)) ;
idelta_sum /= (4 * IDELTA_COUNT) ;
if (bpred == 0 || idelta_sum < best_idelta)
{ best_bpred = bpred ;
best_idelta = idelta_sum ;
} ;
if (! idelta_sum)
{ best_bpred = bpred ;
best_idelta = 16 ;
break ;
} ;
} ; /* for bpred ... */
if (best_idelta < 16)
best_idelta = 16 ;
block_pred [chan] = best_bpred ;
idelta [chan] = best_idelta ;
} ;
return ;
} /* choose_predictor */