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/*
* gbsplay is a Gameboy sound player
*
* 2003-2006 (C) by Tobias Diedrich <ranma+gbsplay@tdiedrich.de>
* Licensed under GNU GPL.
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "impulsegen.h"
static double sinc(double x)
{
double a = M_PI*x;
if (a == 0.0) return 1.0;
return sin(a)/a;
}
static double blackman(double n, double m)
{
return 0.42 - 0.5 * cos(2*n*M_PI/m) + 0.08 * cos(4*n*M_PI/m);
}
short *gen_impulsetab(long w_shift, long n_shift, double cutoff)
{
long i;
double j;
long width = 1 << w_shift;
long n = 1 << n_shift;
long m = width/2;
long size = width*n*sizeof(short);
short *pulsetab = malloc(size);
short *ptr = pulsetab;
if (!pulsetab)
return NULL;
for (j=0; j<1.0; j+=1.0/n) {
long sum=0;
long corr;
long n = 0;
double div = IMPULSE_HEIGHT;
double dcorr = cutoff;
do {
sum = 0;
for (i=-m+1; i<=m; i++) {
double xd = dcorr*IMPULSE_HEIGHT*sinc((i-j)*cutoff)*blackman(i-j+width/2,width);
short x = rint(xd);
sum += x;
}
corr = IMPULSE_HEIGHT - sum;
dcorr *= 1.0 + corr / div;
div *= 1.3;
} while ((corr != 0) && (n++ < 20));
sum = 0;
for (i=-m+1; i<=m; i++) {
double xd = dcorr*IMPULSE_HEIGHT*sinc((i-j)*cutoff)*blackman(i-j+width/2,width);
short x = rint(xd);
*(ptr++) = x;
sum += x;
}
*(ptr - m) += IMPULSE_HEIGHT - sum;
}
return pulsetab;
}
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