Attachment 7191 Details for Bug 15936 – C program showing an slow behavior of sin/cos

C program showing an slow behavior of sin/cos

bug-avx.c (text/x-csrc), 1.62 KB, created by Francesc Alted on 2013-09-06 09:53:01 UTC

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Creator: Francesc Alted

Created: 2013-09-06 09:53:01 UTC

Size: 1.62 KB

patch

obsolete

>/* ####################################################################### */
>/* This script compares the speed of the computation of a polynomial       */
>/* in C in a couple of different ways.                                     */
>/*                                                                         */
>/* Author: Francesc Alted                                                  */
>/* Date: 2013-09-04                                                        */
>/* ####################################################################### */
>
>
>#include <stdio.h>
>#include <math.h>
>#include <unistd.h>
>#include <sys/time.h>
>#include <fenv.h>
>#include <time.h>
>#include <string.h>
>
>#define N  10*1000*1000
>
>double x[N];
>double y[N];
>
>/* Given two timeval stamps, return the difference in seconds */
>float getseconds(struct timeval last, struct timeval current) {
>  int sec, usec;
>
>  sec = current.tv_sec - last.tv_sec;
>  usec = current.tv_usec - last.tv_usec;
>  return (float)(((double)sec + usec*1e-6));
>}
>
>int main(void) {
>  long i;
>  double inf_ = 0;
>  double dN = 2./N;
>  struct timeval last, current;
>  float tspend;
>
>  /* Initialize array */
>  for(i=0; i<N; i++) {
>    x[i] = inf_ + i*dN;
>  }
>
>  /* Commit the y vector (just to be fair with the Python counterparts) */
>  memset(y, 0, sizeof(y));
>
>  /* Perform actual computation */
>  printf("Starting computation...\n");
>  gettimeofday(&last, NULL);
>  for(i=0; i<N; i++) {
>    double t_c = cos(x[i]);
>    double t_s = sin(x[i]);
>    y[i] = t_s * t_s + t_c * t_c;
>  }
>  gettimeofday(&current, NULL);
>  tspend = getseconds(last, current);
>  printf("Compute time:\t %.3f s\n", tspend);
>
>  return(0);
>}
>

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Attachments on bug 15936: 7191