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Re: GCC beaten by ICC in stupid trig test!

Toon Moene wrote:

Laurent GUERBY wrote:

All Monte Carlo based algorithms are also likely to be in
the -ffast-math category. You're happy with 3-4 digits
of "accuracy" thanks to 1/sqrt(n) convergence :).

Another example is all computation where reducing the continuous physics to discrete mathematics already introduced truncation errors larger than any floating point rounding error at 24 bit mantissa precision.

Well I don't know exactly what stuff is in -ffast-math, but I suspect it is a mistake to just think in terms of rounding error vs the mantissa length. For example, if -ffast-math is so sloppy as to consider
that (a+b)+c can be replaced by a+(b+c), then all bets are off.
It is easy to construct cases where the former has a value of 1.0
and the latter has a value of 0.0.



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