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copied!<ul> <li>This function is perfectly amenable to SIMD processing. Look into your compiler documentation for the intrinsic functions that correspond to the SSE instructions.</li> <li>You could break up the dependence chain on the <code>sum</code> variable. Instead of a single <code>sum</code> accumulator, use two accumulators <code>sum1</code> and <code>sum2</code> alternately - one for even, one for odd indices. Add them up afterwards.</li> <li>The single biggest performance bottleneck here is the <code>log()</code> function. Check if an approximation would be sufficient. The calculation of this could also be vectorized - I believe Intel published a high-performance math library - including vectorized versions of functions like <code>log()</code>. You may like to use this.</li> <li>You are operating on <code>float</code>s here, and <code>log()</code> uses <code>double</code> precision. Use <code>logf()</code> instead. It may (or may not) be faster. It will certainly be no slower.</li> <li>If your compiler understands C99, place a <code>restrict</code> qualifier on the pointers which are function arguments. This tells the compiler that those arrays do not overlap, and may help it generate more efficient code.</li> <li>Change the way matrices are kept in memory. Instead of an array of pointers pointing to disjoint memory blocks, use a single array M*N elements in size.</li> </ul> <p>So, to put it together, this is how the function should look like. This is portable C99. Using the compiler-specific SIMD intrinsics, this could be made WAAAAY faster.</p> <p><strong>UPDATE:</strong> Note that I changed the way input matrices are defined. A matrix is a single, large array.</p> <pre><code>float fnFrequentFunction(const float *restrict x, const float *restrict y, const float *restrict z, const float *restrict a, const float *restrict b, float *restrict c, int n) { float ret = 0; const float *restrict yy = y; //for readability const float *restrict zz = z; // -||- for (int i = 0; i < n; i++, yy += M, zz += M) // n == 1, 2, 4, or 8 { float sum = 0; float sum2 = 0; for(int j = 0; j < 10; j += 2) { float tmp = x[j] - yy[j]; sum += tmp * tmp * zz[j]; float tmp2 = x[j+1] - yy[j+1]; sum2 += tmp2 * tmp2 * zz[j+1]; } sum += sum2; ret += (c[i] = logf(a[i] * b[i]) + sum); } return ret; } </code></pre>

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