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Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication



On 05/10/2004, at 2:08 PM, Dale Johannesen wrote:


On 05/10/2004, at 1:12 PM, Gabriel Dos Reis wrote:

Geoffrey Keating <geoffk@geoffk.org> writes:
That flag is clearly the right flag to pick. See the explanation he gave.
It contains an example that illustrates the problem too.

Fariborz said


For different values of "x" this leads to undeserved or absent floating point exceptions

So, why not flag_trapping_math? The case involves an infinity, what about flag_finite_math_only?

It is not just exceptions. It is possible that X* (C*C) would overflow, or lose some low-order bits,
where (X*C)*C would not, for large C and small X.

OK. I am not going to re-design Fariborz's patch for him in an e-mail exchange. It is clear that the explanation of the patch is inadequate to determine whether or not the patch is correct, so the patch is rejected. Fariborz, please re-post the patch with a better explanation, and addressing the other points I mentioned.

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