/* link with -lm */

#define _XOPEN_SOURCE 500

#include <stdio.h>

#include <math.h>

#include <complex.h>

#include <time.h>

double mycos (double rads) {

double perc = fabs(rads / M_PI);

/* perc may be zero. C declares 0 ** 0 == NaN.

** use the same point on the next cycle instead.

*/

perc = perc ? perc : 2;

return pow(perc, perc) * creal(cpow(-perc, -perc));

}

double clock_diff (struct timespec *b, struct timespec *a) {

return a->tv_sec - b->tv_sec

+ (float)(a->tv_nsec - b->tv_nsec) / 1000000000;

}

int main (void) {

struct timespec before, after;

double trash;

clock_gettime(CLOCK_MONOTONIC_RAW, &before);

for (float i = 0; i < 2 * M_PI; i += (float)M_PI / 1000000) trash = cos(i);

clock_gettime(CLOCK_MONOTONIC_RAW, &after);

float time_a = clock_diff(&before, &after);

printf("cos() took %f seconds\n", time_a);

clock_gettime(CLOCK_MONOTONIC_RAW, &before);

for (float i = 0; i < 2 * M_PI; i += (float)M_PI / 1000000) trash = mycos(i);

clock_gettime(CLOCK_MONOTONIC_RAW, &after);

float time_b = clock_diff(&before, &after);

printf("mycos() took %f seconds\n", time_b);

trash = trash;

printf("mycos() takes approximately %.15f times longer to run than cos()\n",

time_b / time_a

);

puts("sanity:");

for (float i = 0; i < 2 * M_PI; i += 1) {

printf("cos (%.15f):\t%+.15f\n", i, cos(i));

printf("mycos(%.15f):\t%+.15f\n", i, mycos(i));

}

return 0;

}