lfsr.c

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/******************************************************************************/
/******************************************************************************/

#include "lfsr.h"

void
lfsr_init_start_state(
    uint16_t    seed,
    lfsr_t      *instance
) {
    instance->start_state   = seed;
    instance->lfsr_value    = seed;
}

uint16_t
lfsr_get_next(
    lfsr_t *instance
) {
    unsigned lsb = instance->lfsr_value & 1;/* Get LSB (i.e., the output bit). */

    instance->lfsr_value >>= 1; /* Shift register */

    if (lsb == 1) {
        /* Only apply toggle mask if output bit is 1 */
        instance->lfsr_value ^= 0xB400u;/* Apply toggle mask, value has 1 at bits corresponding
                                                    * to taps, 0 elsewhere. */
    }

    return instance->lfsr_value;
}

void
lfsr_reset(
    lfsr_t *instance
) {
    instance->lfsr_value = instance->start_state;
}