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Why does this bit of code, const float x[16] = { 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6}; const float z[16] = {1.123, 1.234, 1.345, 156.467, 1.578, 1.689, 1.790, 1.812, 1.923, 2.034, 2.145, 2.256, 2.367, 2.478, 2.589, 2.690}; float y[16]; for (int i = 0; i < 16; i++) { y[i] = x[i]; } for (int j = 0; j < 9000000; j++) { for (int i = 0; i < 16; i++) { y[i] *= x[i]; y[i] /= z[i]; y[i] = y[i] + 0.1f; // <-- y[i] = y[i] - 0.1f; // <-- } } run more than 10 times faster than the following bit (identical except where noted)? const float x[16] = { 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6}; const float z[16] = {1.123, 1.234, 1.345, 156.467, 1.578, 1.689, 1.790, 1.812, 1.923, 2.034, 2.145, 2.256, 2.367, 2.478, 2.589, 2.690}; float y[16]; for (int i = 0; i < 16; i++) { y[i] = x[i]; } for (int j = 0; j < 9000000; j++) { for (int i = 0; i < 16; i++) { y[i] *= x[i]; y[i] /= z[i]; y[i] = y[i] + 0; // <-- y[i] = y[i] - 0; // <-- } } when compiling with Visual Studio 2010 SP1. The optimization level was -02 with sse2 enabled. I haven't tested with other compilers.

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