jgoenetxea
4/26/2018 - 3:05 PM

Benchmark various sigmoid functions

Benchmark various sigmoid functions

``````#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <math.h>

#define M_PI_2        1.57079632679489661923	/* pi/2 */
#define M_PI_2_INV    (1.0/M_PI_2)
#define M_2_SQRTPI    1.12837916709551257390    /* 2/sqrt(pi) */
#define ERF_COEF      (1.0/M_2_SQRTPI)

const int SIZE=100;
const int CYCLES=10000000;

double benchmark(const char* name, double (*fun)(double)) {
clock_t start, stop;
double xs[SIZE];
double t_ns;

for (int i=0; i<SIZE; i++) {
xs[i] = rand();
}

start = clock();
for (int repeat=0; repeat<CYCLES; repeat++) {
for (int i=0; i<SIZE; i++) {
(*fun)(xs[i]);
}
}
stop = clock();
t_ns = (stop-start)*1.0e9/CLOCKS_PER_SEC/CYCLES/SIZE;
printf("%-17s %6.1f ns\n", name, t_ns);
return t_ns;
}

double with_atan(double x) {
/* normalized atan */
return M_PI_2_INV*atan(M_PI_2*x);
}

double with_exp(double x) {
return 1.0/(1.0 + exp(-x));
}

double with_sqrt(double x) {
return 1.0/sqrt(1.0 + x*x);
}

double with_erf(double x) {
return erf(ERF_COEF*x);
}

double with_fabs(double x) {
return x/(1.0 + fabs(x));
}

int main(int argc, char **argv) {
benchmark("atan(pi*x/2)*2/pi", with_atan);
benchmark("atan(x)", atan);
benchmark("1/(1+exp(-x))", with_exp);
benchmark("1/sqrt(1+x^2)", with_sqrt);
benchmark("erf(sqrt(pi)*x/2)", with_erf);
benchmark("tanh(x)", tanh);
benchmark("x/(1+|x|)", with_fabs);
}

``````