Thread safe random numbers in c

thread_safe_random_numbers.c

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

//#define NUM_THREADS 7

// Thread safe random numbers by tempering the upper 32 bits
// of a 64 bit int.  The calculations are based on a seed.
//
// Create a single seed per thread and use that for every call 
// lcg64_temper.
//
// credit: http://stackoverflow.com/a/19083740/2635342
static int32_t temper(int32_t x)
{
	x ^= x>>11;
	x ^= x<<7 & 0x9D2C5680;
	x ^= x<<15 & 0xEFC60000;
	x ^= x>>18;
	return x;
}

int32_t lcg64_temper(uint64_t *seed)
{
	*seed = 6364136223846793005ULL * *seed + 1;
	return temper(*seed >> 32);
}

int threadFunction(void* data)
{
	int32_t id = *(int32_t*)data;
	printf("%d-th thread up\n", id);

	uint64_t threadSeed = time(NULL) ^ id;

	int32_t n = lcg64_temper(&threadSeed) % 20 + 1;
	thrd_sleep(&(struct timespec){ .tv_sec = n }, NULL); // Sleep for a random number of seconds.

	printf("%d-th thread done\n", id);
	return 0;
}


int main(void)
{
	const size_t NUM_THREADS = 7;

	int32_t threadData[NUM_THREADS];
	thrd_t threads[NUM_THREADS];

	// Initialize data for each thread.
	for (size_t i = 0; i < NUM_THREADS; ++i)
	{
        	threadData[i] = i;
	}

	// Create the threads.
	for (size_t i = 0; i < NUM_THREADS; ++i)
	{
		if (thrd_create(threads+i, threadFunction, threadData+i) != thrd_success)
		{
			printf("%zu-th thread create error\n", i);
            		return 1;
		}
	}

	// Wait for all threads to complete.
	for (size_t i = 0; i < NUM_THREADS; ++i)
		thrd_join(threads[i], NULL);

	return 0;
}