1 files changed, 93 insertions, 0 deletions
diff --git a/multimedia/munt/interleave.c b/multimedia/munt/interleave.c
new file mode 100644
index 0000000000..20b666ae12
--- /dev/null
+++ b/multimedia/munt/interleave.c
@@ -0,0 +1,93 @@
+/* interleave.c - B. Watson, April 2023, WTFPL licensed.
+
+   Given two files of the same size, creates a 3rd file whose contents are:
+
+   file 1, byte 1
+   file 2, byte 1
+   file 1, byte 2
+   file 2, byte 2
+   file 1, byte 3
+   file 2, byte 3
+   ...etc.
+
+   If file1 contains "foo" and file2 contains "bar", the output will
+   be "fboaor". The output is always twice the size of one of the
+   input files (or, the same size as both input files combined).
+
+   Output file is silently overwritten if it already exists.
+
+   Exit status is 0 for success, non-zero for failure, with a hopefully
+   useful error message.
+
+   Compile me with:
+     gcc -Wall -O2 -o interleave interleave.c
+
+   This could be done more efficiently and without an artificial file
+   size limit, but the current implementation reads everything into a
+   statically sized buffer for simpliticy.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#define MAX_SIZE (1024 * 1024)
+
+unsigned char blob1[MAX_SIZE + 1], blob2[MAX_SIZE + 1], output[MAX_SIZE * 2 + 1];
+
+void die(const char *msg) {
+	if(msg)
+		fprintf(stderr, "interleave: %s\n", msg);
+	else
+		perror("interleave");
+	exit(1);
+}
+
+int read_file(const char *fname, unsigned char *dest) {
+	int bytes;
+	FILE *f = fopen(fname, "rb");
+
+	if(!f) die(NULL);
+	if( (bytes = fread(dest, 1, MAX_SIZE + 1, f)) < 1 ) die(NULL);
+	fclose(f);
+
+	/* fprintf(stderr, "read %d bytes from %s\n", bytes, fname); */
+
+	return bytes;
+}
+
+void write_output(const char *fname, int bytes) {
+	int i;
+	unsigned char *p = output;
+	FILE *f = fopen(fname, "wb");
+
+	if(!f) die(NULL);
+
+	for(i = 0; i < bytes; i++) {
+		*p++ = blob1[i];
+		*p++ = blob2[i];
+	}
+
+	if( (fwrite(output, 1, bytes * 2, f)) < (bytes * 2) ) die(NULL);
+
+	fclose(f);
+}
+
+int main(int argc, char **argv) {
+	int size1, size2;
+
+	if(argc != 4)
+		die("usage:\n\tinterleave <input1> <input2> <output>");
+
+	size1 = read_file(argv[1], blob1);
+	size2 = read_file(argv[2], blob2);
+
+	if(size1 > MAX_SIZE)
+		die("input file too big (max 1MB each)");
+	if(size1 != size2)
+		die("input files are not the same size");
+
+	write_output(argv[3], size1);
+
+	return 0;
+}