Added PDM converter.

The program requires a mono 78670Hz 32-bit-float headerless PCM file.

converter.c

@@ -0,0 +1,90 @@
+#define _CRT_NONSTDC_NO_WARNINGS
+#define _CRT_SECURE_NO_WARNINGS
+#include <io.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+#include <sys/stat.h>
+
+#define BITS 8
+
+void main(int argc, const char *argv[])
+{
+    if (argc != 2)
+    {
+        fprintf(stderr, "usage: %s file\n", argv[0]);
+        return;
+    }
+
+    char name[256];
+
+    sprintf(name, "%s.raw", argv[1]);
+    int source = open(name, O_RDONLY | O_BINARY);
+    fprintf(stderr, "source: %s\n", name);
+    if (source == -1)
+    {
+        perror("source");
+        return;
+    }
+
+    sprintf(name, "%s.a2stream", argv[1]);
+    int target = open(name, O_WRONLY | O_BINARY | O_CREAT | O_TRUNC, S_IREAD | S_IWRITE);
+    fprintf(stderr, "target: %s\n", name);
+    if (target == -1)
+    {
+        close(source);
+        perror("target");
+        return;
+    }
+
+    int samples = 0;
+    int size;
+    float error = 0.0;
+    bool last = false;
+    do
+    {
+        float x[256 * BITS];
+        size = read(source, x, sizeof(x)) / sizeof(float);
+        if (size == -1)
+        {
+            perror("source");
+            close(source);
+            close(target);
+            return;
+        }
+
+        unsigned char y[256];
+        memset(y, 0, sizeof(y));
+
+        // first-order delta-sigma converter
+        for (int n = 0; n < size; n++)
+        {
+            bool next = x[n] >= error;
+            error = (next ? 1.0 : -1.0) - x[n] + error;
+            if (next != last)
+            {
+                y[n / BITS] |= 1 << (n % BITS);
+            }
+            last = next;
+        }
+
+        if (write(target, y, size / BITS) != size / BITS)
+        {
+            perror("target");
+            close(source);
+            close(target);
+            return;
+        }
+
+        samples += size;
+        int h = (samples / 78670 / 3600);
+        int m = (samples / 78670 /   60) % 60;
+        int s = (samples / 78670       ) % 60;
+        fprintf(stderr, "offset: %02d:%02d:%02d\r", h, m, s);
+    }
+    while (size);
+
+    close(source);
+    close(target);
+}