81 lines
2.0 KiB
C
81 lines
2.0 KiB
C
/*
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* Pretend to be a modem by throttling output.
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*
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* 2023-09-12
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* Neale Pickett <neale@woozle.org>
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*
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* To the extent possible under law,
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* I waive all copyright and related or neighboring rights to this software.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <stddef.h>
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#include <sysexits.h>
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#include <unistd.h>
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const int MICROSECOND = 1;
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const int MILLISECOND = 1000 * MICROSECOND;
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const int SECOND = 1000 * MILLISECOND;
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const int NOISINESS_DENOMINATOR = 36000;
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const int NOISELEN_DEFAULT = 16;
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int
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usage(char *me, char *error) {
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if (error) {
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fprintf(stderr, "ERROR: %s\n", error);
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}
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fprintf(stderr, "Usage: %s BAUD [NOISINESS] [NOISELEN]\n", me);
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fprintf(stderr, "\n");
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fprintf(stderr, "Reads stdin, and writes it back to stdout at BAUD bits per second.\n");
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fprintf(stderr, "\n");
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fprintf(stderr, "NOISINESS\tEvery bit can begin line noise, with probability NOISINESS/%d\n", NOISINESS_DENOMINATOR);
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fprintf(stderr, "NOISELEN\tUp to this many bits of noise happens per burst (default: %d)\n", NOISELEN_DEFAULT);
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return EX_USAGE;
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}
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int
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main(int argc, char *argv[]) {
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if (argc < 2) {
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return usage(argv[0], NULL);
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}
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int baud = atoi(argv[1]);
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if (baud < 1) {
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return usage(argv[0], "Invalid baud rate");
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}
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int noisiness = 0;
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if (argc > 2) {
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noisiness = atoi(argv[2]);
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}
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int noiselen = NOISELEN_DEFAULT;
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if (argc > 3) {
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noiselen = atoi(argv[3]);
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}
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int cps = baud / 10; // 8N1 has 10 bits per octet: 8 data, 1 start, 1 parity
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int delay = SECOND / cps;
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int noisybits = 0;
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int c;
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while ((c = getchar()) != EOF) {
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usleep(delay);
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for (int bit = 0; bit < 8; bit++) {
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int r = rand() % NOISINESS_DENOMINATOR;
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if (r < noisiness) {
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noisybits = rand() % noiselen;
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}
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if (noisybits) {
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c ^= (rand() & 1) << bit;
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noisybits -= 1;
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}
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}
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putchar(c);
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fflush(stdout);
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}
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return EX_OK;
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}
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