Time mesurement for decimal to binary change function.

time_dec2bin.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <mach/mach_time.h>

#define DEBUG 0

int digit3(unsigned long n)
{
        if ( n == 0 ) return 1;
	int max = sizeof(unsigned long)*8;
	for ( int i = 0; i < max; i++, n>>=1 ) {
		if (n==0) {
			return i;
		} 
	}
	return 1;
}

int digit2(unsigned long n)
{
	if ( n == 0 ) return 1;
	int max = sizeof(unsigned long)*8;
	unsigned long mask = (unsigned long)1<<(max-1);
#if DEBUG
	printf("%d %lx %lx\n",max,mask,n);
#endif
	for ( int i = max; i > 0; i--,mask>>=1 ) {
		if (n&mask) {
			return i;
		} 
	}
	return 1;
}

int digit(unsigned long n)
{
	if ( n == 0 ) return 1;
	int k = (int)(log2(n));
	return k+1;
}

char *binary(long decimal,char *buff,int length)
{
	int d = digit(decimal);
#if DEBUG
	printf("digit = %d\n",d);
#endif
	if ( buff == NULL || length == 0 ) {
		buff = malloc(d+1);
	}
	buff[d] = 0;
	for ( int i = 0; i < d; i++ ) {
		if ( ( decimal >> (d-i-1) ) % 2 ) {
			buff[i] = '1';
		} else {
			buff[i] = '0';
		}
	}
#if DEBUG
	printf("decimal = %ld\n",decimal);
	printf("binary = %s\n",buff);
#endif
	return buff;
}

int main(int argc,char *argv[])
{
	if ( argc < 2 ) {
		fprintf(stderr,"Usage : %s repeat_count\n",argv[0]);
		return -1;
	}
	srandom((unsigned int)time(NULL));
	int count = atoi(argv[1]);
	char result[sizeof(long)*8+1];
	uint64_t start, elapsed;
	mach_timebase_info_data_t base;
	mach_timebase_info(&base);
	start = mach_absolute_time();

	for ( int i = 0; i < count; i++ ) {
		long decimal = (long)random();
#if DEBUG
		decimal &= 0x0ffff;
#endif
		binary(decimal,result,sizeof(result));
	}
	elapsed = mach_absolute_time() - start;
	uint64_t nsec = elapsed * base.numer / base.denom;
	printf("time = %lld(nsec) : count = %d\n",nsec,count);
	printf("time = %lld(nsec)\n",nsec/count);

	return 0;
}