test.c

#include <math.h>

#ifdef USE_RESTRICT
#else
#define __restrict
#endif


void transform (float * __restrict dest, float * __restrict src, 
                float * __restrict matrix, int n) __attribute__ ((noinline));

void transform (float * __restrict dest, float * __restrict src, 
                float * __restrict matrix, int n)
{
  int i;

  // simple transform loop.

  // written with aliasing in mind. dest, src and matrix 
  // are potentially aliasing, so the compiler is forced to reload
  // the values of matrix and src for each iteration.

  for (i=0; i<n; i++)
  {
    dest[0] = src[0] * matrix[0] + src[1] * matrix[1] + 
              src[2] * matrix[2] + src[3] * matrix[3];

    dest[1] = src[0] * matrix[4] + src[1] * matrix[5] + 
              src[2] * matrix[6] + src[3] * matrix[7];

    dest[2] = src[0] * matrix[8] + src[1] * matrix[9] + 
              src[2] * matrix[10] + src[3] * matrix[11];

    dest[3] = src[0] * matrix[12] + src[1] * matrix[13] + 
              src[2] * matrix[14] + src[3] * matrix[15];

    src  += 4;
    dest += 4;
  }
}

float srcdata[4*10000];
float dstdata[4*10000];

int main (int argc, char**args)
{
  int i,j;
  float matrix[16];

  // init all source-data, so we don't get NANs  
  for (i=0; i<16; i++)   matrix[i] = 1;
  for (i=0; i<4*10000; i++) srcdata[i] = i;

  // do a bunch of tests for benchmarking. 
  for (j=0; j<10000; j++)
    transform (dstdata, srcdata, matrix, 10000);
}