Re: Has anyone noticed -ffast-math (gcc) fights against NaN's?

[Taj Khattra <taj.khattra@...>]

> I've been revising the LNUM patch (more of that later) and spend several
> hours today trying to understand what exactly -ffast-math does with regard
> to NaN's (not-a-numbers).

from the gcc docs:

`-ffast-math'
     Sets `-fno-math-errno', `-funsafe-math-optimizations',
     `-fno-trapping-math', `-ffinite-math-only', `-fno-rounding-math'
     and `-fno-signaling-nans'.

     This option causes the preprocessor macro `__FAST_MATH__' to be
     defined.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications for math
     functions.

`-ffinite-math-only'
     Allow optimizations for floating-point arithmetic that assume that
     arguments and results are not NaNs or +-Infs.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications.

     The default is `-fno-finite-math-only'.