Re: [PATCH v3] Don't spin around multiplying zeroes in __mul

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

On Wed, Jan 16, 2013 at 07:18:20AM -0600, Ryan S. Arnold wrote:
> Siddhesh, What are you running to gather your performance numbers? I'd
> like to do a comparison on Power.
> 

I'm using the program below, which is modified from:

http://entropymine.com/imageworsener/slowpow/

The method of getting the numbers is the same as the benchmark suite
patch I had posted, i.e. using CLOCK_MONOTONIC_RAW around the function
call over multiple calls and getting the average, so it should get the
same results.

The input I use is:

./powtest 100000 1.0000000000000020 1.5000000000000000

which for x86_64 hits the slowest computation path, which uses a
precision of 32 mantissa digits in mp_no, i.e. 768bits.  For Power,
you might want to make sure that it escapes the ldbl code and actually
enters the mp code; I think it does, but I don't remember right now.


Siddhesh


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

struct timespec start, end;

int main(int argc,char**argv)
{
  int i;
  volatile double b, e, x;
  uint64_t total = 0, max = 0, min = 0x7fffffffffffffff, count;
  double avg;

  if (argc<4) { printf("error\n"); return 1; }
  count = atoi(argv[1]);
  b = atof(argv[2]);
  e = atof(argv[3]);

  for (i=0;i<count;i++) {
    clock_gettime(CLOCK_REALTIME, &start);
    x = pow(b,e);
    clock_gettime(CLOCK_REALTIME, &end);
    uint64_t diff = end.tv_nsec - start.tv_nsec + 1000000000 * (end.tv_sec - start.tv_sec);

    if (diff > max)
      max = diff;
    if (diff < min)
      min = diff;
    total += diff;
  }
  printf("(count=%d) %.16f^%.16f = %.16f\n",count,b,e,x);
  printf ("Total:%lld, Fastest:%lld, Slowest:%lld, Avg:%lf\n",
	  total, min, max, (double) total / count);
  return 0;
}