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/*
* July 5, 1991
* Copyright 1991 Lance Norskog And Sundry Contributors
* This source code is freely redistributable and may be used for
* any purpose. This copyright notice must be maintained.
* Lance Norskog And Sundry Contributors are not responsible for
* the consequences of using this software.
*/
/*
* Sound Tools rate change effect file.
*/
#include <math.h>
#include "st.h"
/*
* Least Common Multiple Linear Interpolation
*
* Find least common multiple of the two sample rates.
* Construct the signal at the LCM by interpolating successive
* input samples as straight lines. Pull output samples from
* this line at output rate.
*
* Of course, actually calculate only the output samples.
*
* LCM must be 32 bits or less. Two prime number sample rates
* between 32768 and 65535 will yield a 32-bit LCM, so this is
* stretching it.
*/
/*
* Algorithm:
*
* Generate a master sample clock from the LCM of the two rates.
* Interpolate linearly along it. Count up input and output skips.
*
* Input: |inskip | | | | |
*
*
*
* LCM: | | | | | | | | | | |
*
*
*
* Output: | outskip | | |
*
*
*/
/* Private data for Lerp via LCM file */
typedef struct ratestuff {
u_l lcmrate; /* least common multiple of rates */
u_l inskip, outskip; /* LCM increments for I & O rates */
u_l total;
u_l intot, outtot; /* total samples in LCM basis */
long lastsamp; /* history */
} *rate_t;
/*
* Process options
*/
rate_getopts(effp, n, argv)
eff_t effp;
int n;
char **argv;
{
if (n)
fail("Rate effect takes no options.");
}
/*
* Prepare processing.
*/
rate_start(effp)
eff_t effp;
{
rate_t rate = (rate_t) effp->priv;
IMPORT long lcm();
rate->lcmrate = lcm((long)effp->ininfo.rate, (long)effp->outinfo.rate);
/* Cursory check for LCM overflow.
* If both rate are below 65k, there should be no problem.
* 16 bits x 16 bits = 32 bits, which we can handle.
*/
rate->inskip = rate->lcmrate / effp->ininfo.rate;
rate->outskip = rate->lcmrate / effp->outinfo.rate;
rate->total = rate->intot = rate->outtot = 0;
rate->lastsamp = 0;
}
/*
* Processed signed long samples from ibuf to obuf.
* Return number of samples processed.
*/
rate_flow(effp, ibuf, obuf, isamp, osamp)
eff_t effp;
long *ibuf, *obuf;
int *isamp, *osamp;
{
rate_t rate = (rate_t) effp->priv;
int len, done;
long *istart = ibuf;
long last;
done = 0;
if (rate->total == 0) {
/* Emit first sample. We know the fence posts meet. */
*obuf = *ibuf++;
rate->lastsamp = *obuf++ / 65536;
done = 1;
rate->total = 1;
/* advance to second output */
rate->outtot += rate->outskip;
/* advance input range to span next output */
while ((rate->intot + rate->inskip) <= rate->outtot){
last = *ibuf++ / 65536;
rate->intot += rate->inskip;
}
}
/* start normal flow-through operation */
last = rate->lastsamp;
/* number of output samples the input can feed */
len = (*isamp * rate->inskip) / rate->outskip;
if (len > *osamp)
len = *osamp;
for(; done < len; done++) {
*obuf = last;
*obuf += ((float)((*ibuf / 65536) - last)* ((float)rate->outtot -
rate->intot))/rate->inskip;
*obuf *= 65536;
obuf++;
/* advance to next output */
rate->outtot += rate->outskip;
/* advance input range to span next output */
while ((rate->intot + rate->inskip) <= rate->outtot){
last = *ibuf++ / 65536;
rate->intot += rate->inskip;
if (ibuf - istart == *isamp)
goto out;
}
/* long samples with high LCM's overrun counters! */
if (rate->outtot == rate->intot)
rate->outtot = rate->intot = 0;
}
out:
*isamp = ibuf - istart;
*osamp = len;
rate->lastsamp = last;
}
/*
* Do anything required when you stop reading samples.
* Don't close input file!
*/
rate_stop(effp)
eff_t effp;
{
/* nothing to do */
}
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