Different output on x86_64 and i686

[erikrk]

Output files generated on different CPU architectures are not identical. This is probably due to rounding errors. The test environment does not handle this. The current MD5 checksums correspond to output generated on x86_64, Consequently, "make check" fails in i686.

[erikrk]

I think this is the reason.

http://www.network-theory.co.uk/docs/gccintro/gccintro_70.html

It's all about the internal precision of the FPU. The x86_64 code uses SSE instructions which use 64-bit precision internally and the i686 code uses x87 instructions which use 80-bit precision internally.

I don't think it really matters for practical purposes, but it's kind of annoying that you get different results.

[mmroden]

Yeah, different outputs for different processors doesn't worry me.
Different outputs for the same processor would be terrifying.

On Wednesday, May 6, 2015, Erik Karlsson [email protected] wrote:

I think this is the reason.

http://www.network-theory.co.uk/docs/gccintro/gccintro_70.html

It's all about the internal precision of the FPU. The x86_64 code uses SSE
instructions which use 64-bit precision internally and the i686 code uses
x87 instructions which use 80-bit precision internally.

I don't think it really matters for practical purposes, but it's kind of
annoying that you get different results.

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