A simple implementation of twitter snowflake in C

snowflake.c

#include<time.h>
#include<unistd.h>

/*
 * snowflake.c
 *
 * a simple implementation of twitter snowflake in C
 *
 * [email protected]
 */

#define BITS 8
#define SEQ 256

unsigned long last = 0;
unsigned char seq = 0;

unsigned long milliseconds();
unsigned long generate();

unsigned long milliseconds() {
    struct timespec spec = {0};
    clock_gettime(CLOCK_REALTIME, &spec);
    return spec.tv_sec * 1000 + spec.tv_nsec / 1000000;
}

unsigned long generate() {
    unsigned long current = 0;
    while (last > (current = milliseconds())) {
        usleep(1000);
    }
    if (last != current) {
        seq = 0;
    } else {
        seq = (seq + 1) % SEQ;
        if (0 == seq) {
            while (last >= (current = milliseconds())) {
                usleep(1);
            }
        }
    }
    last = current;
    return (current << BITS) + seq;
}