I rewrote my modem/baud simulator

content/misc/baud.c

@@ -0,0 +1,84 @@
+/*
+ * Pretend to be a modem by throttling output.
+ *
+ * 2023-09-12 
+ * Neale Pickett <neale@woozle.org>
+ *
+ * To the extent possible under law, 
+ * I waive all copyright and related or neighboring rights to this software.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <sysexits.h>
+#include <unistd.h>
+
+const int MICROSECOND = 1;
+const int MILLISECOND = 1000 * MICROSECOND;
+const int SECOND = 1000 * MILLISECOND;
+
+const int NOISINESS_DENOMINATOR = 36000;
+const int NOISELEN_DEFAULT = 16;
+
+int
+usage(char *me, char *error) {
+    if (error) {
+        fprintf(stderr, "ERROR: %s\n", error);
+    }
+    fprintf(stderr, "Usage: %s BAUD [NOISINESS] [NOISELEN]\n", me);
+    fprintf(stderr, "\n");
+    fprintf(stderr, "Reads stdin, and writes it back to stdout at BAUD bits per second.\n");
+    fprintf(stderr, "\n");
+    fprintf(stderr, "NOISINESS\tEvery bit can begin line noise, with probability NOISINESS/%d\n", NOISINESS_DENOMINATOR);
+    fprintf(stderr, "NOISELEN\tUp to this many bits of noise happens per burst (default: %d)\n", NOISELEN_DEFAULT);
+    return EX_USAGE;
+}
+
+int
+main(int argc, char *argv[]) {
+    if (argc < 2) {
+        return usage(argv[0], NULL);
+    }
+
+    int baud = atoi(argv[1]);
+    if (baud < 1) {
+        return usage(argv[0], "Invalid baud rate");
+    }
+
+    int noisiness = 0;
+    if (argc > 2) {
+        noisiness = atoi(argv[2]);
+    }
+    int noiselen = NOISELEN_DEFAULT;
+    if (argc > 3) {
+        noiselen = atoi(argv[3]);
+    }
+
+    int cps = baud / 8;
+    int delay = SECOND / cps;
+    int noisybits = 0;
+    int c;
+    while ((c = getchar()) != EOF) {
+        usleep(delay);
+        for (int bit = 0; bit < 8; bit++) {
+            int r = rand() % NOISINESS_DENOMINATOR;
+            if (r < noisiness) {
+                noisybits = rand() % noiselen;
+            }
+
+            if (noisybits) {
+                if (rand() < RAND_MAX/2) {
+                    c &= ~(1<<bit);
+                } else {
+                    c |= 1<<bit;
+                }
+                noisybits -= 1;
+            }
+        }
+        putchar(c);
+        fflush(stdout);
+    }
+    
+    return EX_OK;
+}