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/*
tlininterp.c
David Rowe
Jan 2017
Fast linear interpolator for high oversam[pling rates. Upsample
with a decent filter first such that the signal is "low pass" wrt
to the input sample rate.
build: gcc tlininterp.c -o tlininterp -Wall -O2
*/
#include <assert.h>
#include <getopt.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#define NBUF 1000
#define SIGNED_16BIT 0
#define SIGNED_8BIT 1
void display_help(void) {
fprintf(stderr, "\nusage: tlininterp inputRawFile OutputRawFile OverSampleRatio [-c]\n");
fprintf(stderr, "\nUse - for stdin/stdout\n\n");
fprintf(stderr, "-c complex signed 16 bit input and output\n");
fprintf(stderr, "-d complex signed 16 bit input, complex signed 8 bit output\n");
fprintf(stderr, "-f +Fs/4 freq shift\n\n");
}
int main(int argc, char *argv[]) {
FILE *fin, *fout;
short left[2], right[2], out[2*NBUF], i;
float oversample, t;
int8_t out_s8[2*NBUF];
int lo_i[3], lo_q[3];
if (argc < 3) {
display_help();
exit(1);
}
if (strcmp(argv[1], "-") == 0)
fin = stdin;
else
fin = fopen(argv[1], "rb");
assert(fin != NULL);
if (strcmp(argv[2], "-") == 0)
fout = stdout;
else
fout = fopen(argv[2], "wb");
assert(fout != NULL);
oversample = atof(argv[3]);
if (oversample <= 1) {
display_help();
exit(1);
}
int channels = 1;
int freq_shift = 0;
lo_i[0] = -1; lo_i[1] = 0;
lo_q[0] = 0; lo_q[1] = -1;
int format = SIGNED_16BIT;
int opt;
while ((opt = getopt(argc, argv, "cdf")) != -1) {
switch (opt) {
case 'c': channels = 2; break;
case 'd': channels = 2; format = SIGNED_8BIT; break;
case 'f': freq_shift = 1; break;
default:
display_help();
exit(1);
}
}
for (i=0; i<channels; i++)
left[i] = 0;
t = 0.0;
int j = 0;
while(fread(&right, sizeof(short)*channels, 1, fin) == 1) {
while (t < 1.0) {
for (i=0; i<channels; i++) {
out[2*j+i] = (1.0 - t)*left[i] + t*right[i];
}
if (freq_shift) {
/* update local osc recursion */
lo_i[2] = -lo_i[0]; lo_q[2] = -lo_q[0];
/* complex mixer to up-shift complex samples */
int a = out[2*j];
int b = out[2*j+1];
int c = lo_i[2];
int d = lo_q[2];
out[2*j] = a*c - b*d;
out[2*j+1] = b*c + a*d;
//fprintf(stderr, "% d % d % 5d % 5d\n", lo_i[2], lo_q[2], out[0], out[1]);
/* update LO memory */
lo_i[0] = lo_i[1]; lo_i[1] = lo_i[2];
lo_q[0] = lo_q[1]; lo_q[1] = lo_q[2];
}
/* once we have enough samples write to disk */
j++;
if (j == NBUF) {
if (format == SIGNED_16BIT) {
fwrite(&out, sizeof(short)*channels, NBUF, fout);
} else {
for (i=0; i<channels*NBUF; i++) {
out_s8[i] = out[i] >> 8;
}
fwrite(&out_s8, sizeof(int8_t)*channels, NBUF, fout);
}
j = 0;
}
t += 1.0/oversample;
}
t -= 1.0;
for (i=0; i<channels; i++)
left[i] = right[i];
}
/* write remaining samples to disk */
if (format == SIGNED_16BIT) {
fwrite(&out, sizeof(short), j, fout);
} else {
for (i=0; i<j; i++) {
out_s8[i] = out[i] >> 8;
}
fwrite(&out_s8, sizeof(int8_t), j, fout);
}
fclose(fout);
fclose(fin);
return 0;
}
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