Comparison of strlen and for(;;buf++)

strlen-bench.c

/*
	Compile me:
	$	gcc -Wall -o strlen-bench strlen-bench.c -lrt -g -ggdb -O3
*/

#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include <time.h>
#include <endian.h>

const char *x = "HTTP/0.9 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
                "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\nxxxxxxxxxxxxxxx"
                "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\n";

typedef int (*testfunc)( const char *buf );

typedef union {
	const unsigned char *c;
	const uint32_t *i;
	const uint64_t *q;
	const char *_c1;
} uniptr;


static int test1(const char *buf) {
	const char *p = buf;
	for (;;p++) {
		if (*p ==0) return p-buf;
	}
	return 0;
}

static int test2(const char *buf) {
	return strlen(buf);
}

typedef struct {
	time_t      sec;
	long int    nsec;
	intmax_t    delta;
} mytimediff;

mytimediff timedelta( struct timespec t1, struct timespec t2 ) {
	mytimediff d;
	intmax_t delta_nsec = ( (intmax_t)t2.tv_nsec - (intmax_t)t1.tv_nsec );
	intmax_t delta_sec = (intmax_t)t2.tv_sec - (intmax_t)t1.tv_sec;
	if (delta_nsec < 0) { delta_nsec += 1E9; delta_sec -=1; }
	if (delta_sec < 0) { delta_nsec = 1E9 - delta_nsec; }
	intmax_t delta = delta_sec*1E9 + delta_nsec;
	
	d.sec   = delta_sec;
	d.nsec  = delta_nsec;
	d.delta = delta;
	return d;
}

long double timeit( intmax_t maxtime, testfunc test, const char * data ) {
	struct timespec t0,t1,t2;
	mytimediff d;
	intmax_t i,k, total;
	
	clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &t0);
	long double ops;
	for ( i = 1; i < 0xfffffff ; i <<= 1 ) {
		clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &t1);
		
		for ( k=0; k < i; k++) {
			test(data);
		}
		
		clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &t2);
		
		total += i;
		
		d = timedelta( t1,t2 );
		ops = i*1E9/d.delta;
		
		d = timedelta( t0,t2 );
		
		if ( d.delta > maxtime ) {
			printf(" delta = %jd.%09jds (%jd us); (ops = %.0Lf/s)\n", d.sec, d.nsec, d.delta, ops );
			return ops;
			break;
		}
		
	}
	return -1;
}

int main(void) {
	//return;
	const char *test = x;
	printf("test1 = %d\n", test1(test));
	printf("test2 = %d\n", test2(test));
	
	long double ops1 = timeit( 1E09, test1, test );
	long double ops2 = timeit( 1E09, test2, test );
	
	printf("ops1 = %Lf\n", ops1);
	printf("ops2 = %Lf\n", ops2);
	printf("ops2/ops1 = ( %+0.2Lf%% = x%0.1Lf )\n", 100.0 * ( ops2 - ops1 ) / ops1, ops2/ops1 );
	printf("ops1/ops2 = ( %+0.2Lf%% = x%0.1Lf )\n", 100.0 * ( ops1 - ops2 ) / ops2, ops1/ops2 );
	
	return 0;
}