Am 22.11.18 um 18:30 schrieb Will Godfrey:
While testing some mixed floating point and integer calculations I found a quite surprising difference when this compiler option was set (gcc 6.x). It was clearly different at only 100 iterations and got dramatically worse with larger counts.My test routine was this: int a = 0; float b = 0; float c = 0; float inc = 0.1f; float dec = 0.05f; int it = 100; for (int i = 0; i < it; ++ i) { a = (int)truncf(b); c = b - floorf(b); b += inc; a = (int)truncf(b); c = b - floorf(b); b -= dec; } cout << "int " << a << " rem " << c << endl; My suspicion is that the difference is due to accumulated rounding errors. Curiously without the decrements the behavior with and without -ffast-math seems to be identical well into the millions.
In the guitarix project we've disabled -ffast-math several years ago, when I remember right it was at gcc3, as it could lead to different un-reproduciable calculations. Last option I've disabled on gcc8 now, is -ffinite-math-only, this one leads to nan's and inf's in several cases, which been as well not reproducible.
_______________________________________________ Linux-audio-dev mailing list Linux-audio-dev@lists.linuxaudio.org https://lists.linuxaudio.org/listinfo/linux-audio-dev
