[Python-modules-team] Bug#861249: FTBFS: math_test.Vector2TypeTest.test_cross fails

[René Dudfield]

Hello,

this has been fixed in pygame upstream here:
https://github.com/pygame/pygame/pull/391/commits/630b40ecd7be4ac5583d9ace0ad125190c6abf33

It will be part of the pygame 1.9.4 upstream release.

best regards,



On Sun, 21 May 2017 21:50:58 +0100 Edmund Grimley Evans <
edmund.grimley.evans at gmail.com> wrote:
> On arm64 and at least one other architecture, the error says:
>
> -3.2862601528904633e-16 != 0
>
> It looks as though the test is computing (1.2 * 3.4 - 3.4 * 1.2).
>
> Now, the log to base 2 of (1.2 * 3.4) divided by 3.286e-16 is about
> 53.5. There are 52 bits in the mantissa of a 64-bit float, or 53
> including the implicit "1". So I would guess that the error comes from
> multiply and subtract being combined into a single operation, so that
> the error in computing 1.2 * 3.4 is revealed.
>
> If this is a real problem, perhaps "cross" could be implemented in a
> way that prevents multiply-subtract from being used. If it is not a
> real problem, then the test should be made less sensitive, perhaps by
> requiring the absolute value of the result to be less than 1e-12 or
> some other arbitrary epsilon.
>
>
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