polyml 5.5.2-4

[James Clarke]

Hi Gianfranco,

>> I think it’s implemented in glibc, not gcc; certainly fe{g,s}etround are. Should I get in touch with debian-arm?
> 
> probably yes, even if I don't care there are much armel porters there...
> 
> You might end up in asking ftpmaster to remove the armel binary.

Ok, I think I’ve worked out what’s going on. The software floating-point implementation seems to only support FE_NEAREST. On an ARM device without an FPU, fe{g,s}etround are not supported and should return 1. However, if you are running on an ARM device which has an FPU, fe{g,s}etround will change the FPU’s rounding mode and return 0 for success, but because the floating-point operations are done in software, the rounding mode has no effect. In short, there’s no way for polyml to have proper rounding support on armel. Evidence supporting this is below.

On cortex-r5:

    Current rounding: 0
    Setting to FE_UPWARD (4194304): 1     <- rounding mode not supported
    Current rounding: 0
    1.0 / 3.0: 0.333333333333333315
    1.0 / 3.0 * 1.0: 1.000000000000000000
    Current rounding: 0

On cortex-a8:

    Current rounding: 0
    Setting to FE_UPWARD (4194304): 0
    Current rounding: 4194304
    1.0 / 3.0: 0.333333333333333315
    1.0 / 3.0 * 1.0: 1.000000000000000000
    Current rounding: 4194304

Given that libc ships on armel but does not conform to the standard for rounding, would it make sense to ship polyml for armel with this test disabled? It seems a shame not to support armel at all.

Regards,
James
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