swap test

swap.c

#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/time.h>
#include <time.h>

static long long int ts_us()
{
	struct timeval tv;
	struct timezone tz;
	gettimeofday(&tv, &tz);
	return ((long long int)tv.tv_sec * 1000000) + tv.tv_usec;
}

static inline void memswap1(uint8_t *a, uint8_t *b, size_t size)
{
	while(size--) {
		*a ^= *b;
		*b ^= *a;
		*a ^= *b;
		a++;
		b++;
	}
}

static inline void memswap2(uint8_t *a, uint8_t *b, size_t size)
{
	uint8_t v;
	while(size--) {
		v = *b;
		*b = *a;
		*a = v;
		a++;
		b++;
	}
}

int main ()
{
	struct {
		int a, b, c; char d, e; int f;
	} A = {12414, 42542, 253252, 123, 43, 134151},
		  B = {145151, 422, 123141, 12, 45, 13141511};

	/* int A = 10, B = 20; */

	long long int n, b4, af;

	n = 1000000000;
	b4 = ts_us();
	while(n--)
		memswap1((uint8_t *)&A, (uint8_t *)&B, sizeof(A));
	af = ts_us();

	printf("Swap1\nElapsed %lld us\nPer swap: %f ns\n\n",
	       af - b4, (double)(af-b4)/1000000.0);

	n = 1000000000;
	b4 = ts_us();
	while(n--)
		memswap2((uint8_t *)&A, (uint8_t *)&B, sizeof(A));
	af = ts_us();

	printf("Swap2\nElapsed %lld us\nPer swap: %f ns\n\n",
	       af - b4, (double)(af-b4)/1000000.0);

	n = 1000000000;
	b4 = ts_us();
	typeof(A) tmp;
	while(n--) {
		tmp = A;
		A = B;
		B = tmp;
	}
	af = ts_us();

	printf("Swap3\nElapsed %lld us\nPer swap: %f ns\n\n",
	       af - b4, (double)(af-b4)/1000000.0);
}