Add a program to skew an input using a skew control signal.

diff --git a/do-skew.c b/do-skew.c
new file mode 100644 (file)
index 0000000..6062999
--- /dev/null
+++ b/do-skew.c
@@ -0,0 +1,74 @@
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+#include <stdlib.h>
+
+double frac(double x)
+{
+       return x - (int)x;
+}
+
+int main(int argc, char **argv)
+{
+       FILE *in, *skew, *out;
+
+       // open input
+       if (strcmp(argv[1], "-") == 0) {
+               in = stdin;
+       } else {
+               in = fopen(argv[1], "rb");
+               if (in == NULL) {
+                       perror(argv[1]);
+                       exit(1);
+               }
+       }
+
+       // open skew
+       if (strcmp(argv[2], "-") == 0) {
+               skew = stdin;
+       } else {
+               skew = fopen(argv[2], "rb");
+               if (skew == NULL) {
+                       perror(argv[2]);
+                       exit(1);
+               }
+       }
+
+       // open output
+       if (strcmp(argv[3], "-") == 0) {
+               out = stderr;
+       } else {
+               out = fopen(argv[3], "wb");
+               if (in == NULL) {
+                       perror(argv[3]);
+                       exit(1);
+               }
+       }
+
+       short prev_sample, sample = 0;
+       unsigned in_pos = -1;
+       double p = -1.0;
+
+       while (!feof(in) && !feof(skew)) {
+               double delta_p;
+               if (fread(&delta_p, sizeof(double), 1, skew) != 1) {
+                       exit(0);
+               }
+
+               p += delta_p;
+
+               // read samples until we're at the right position
+               while ((unsigned)(ceil(p)) > in_pos) {
+                       prev_sample = sample;
+                       if (fread(&sample, sizeof(short), 1, in) != 1) {
+                               exit(0);
+                       }
+               }
+
+               // linear interpolation (works well since delta_p varies so slowly)
+               double t = frac(p);
+               short intp_sample = prev_sample * (1.0 - t) + sample * t;
+
+               fwrite(&intp_sample, sizeof(short), 1, out);
+       }
+}