m-sequence output as wav file from LFSR

msequence_16_4taps.c

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

/* 
 Run with:
 make msequence_16_4taps && ./msequence_16_4taps 4847 2 | sox -q -t .raw -r 44100 -c 1 -b 16 -e signed-integer - output.wav
 
 
 Uses code from Wikipedia article "Pseudorandom binary sequence"
 Feedback taps from tabulated values at:
 http://www.newwaveinstruments.com/resources/articles/m_sequence_linear_feedback_shift_register_lfsr.htm
 More values:
 15 Stages, 4 taps:
 [15, 14, 9, 8]
 [15, 14, 9, 3]
 [15, 14, 9, 2]
 [15, 14, 8, 5]
 [15, 14, 8, 4]
 31 stages, 6 taps:
 [31, 30, 29, 28, 18, 6]
 [31, 30, 29, 28, 17, 9]
 [31, 30, 29, 28, 17, 7]
 [31, 30, 29, 28, 16, 8]
 [31, 30, 29, 28, 14, 6]
 [31, 30, 29, 28, 14, 3]
 */

void print_binary(uint16_t c) {
	for (size_t i = 8 * sizeof(c); i-- > 0; ) {
		fprintf(stderr, "%d", (c >> i) & 1);
	}
    fprintf(stderr, "\n");
}

int main(int argc, char* argv[]) {
    if (argc < 3) {
        fprintf(stderr, "%s: Error, provide a seed value and symbol length\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    uint16_t start = atoi(argv[1]);
    uint16_t symbol_length = atoi(argv[2]);
    if (symbol_length < 2) {
        fprintf(stderr, "Error: Minimum symbol length is 2. Setting it to 2. (\"%hd\" was entered)\n", symbol_length);
        symbol_length = 2;
    }

	/* Data for symbol output */
    int16_t * symbol_one = malloc(sizeof(int16_t) * symbol_length);
    int16_t * symbol_zero = malloc(sizeof(int16_t) * symbol_length);
    for (size_t i = 0; i < symbol_length; i++) {
        symbol_one[i] = 0x7FFF;
        symbol_zero[i] = -0x7FFF;
    }

    /* Linear Feedback Shift Register */
    uint16_t a = start;
    fprintf(stderr, "First in sequence: ");
    print_binary(a);
    for(size_t i = 1;; i++) {
        uint16_t newbit = ((((a >> 15)
                              ^ (a >> 14)
                              ^ (a >> 9)
                              ^ (a >> 3))
                            & 1));
        a = ((a << 1) | newbit) & 0xffff;
		/* print_binary(a); */

        if (0x1 == newbit) {
            fwrite(symbol_one, sizeof(int16_t), symbol_length, stdout);
        } else {
			fwrite(symbol_zero, sizeof(int16_t), symbol_length, stdout);
        }

        if (a == start) {
            fprintf(stderr, "m-sequency repetition period is %zu\n", i);
            break;
        }

        if (i > 0xfffff) {
            fprintf(stderr, "Max Count Reached.\n");
            exit(EXIT_FAILURE);
        }
    }
    fflush(stdout);
    fclose(stdout);
}