ARM testers, make note.

[Johannes Pfau]

Am Fri, 16 Aug 2013 18:33:14 +0200
schrieb "Iain Buclaw" <ibuclaw at ubuntu.com>:

> I've pushed in pure implementations of functions in std.math, 
> removing the workaround in core.stdc.math.
> 
> This passes for x64/x32. Can any ARM testers please report any 
> problems causecd by this update?
> 
> Thanks
> Iain.

I found a bug in the floor implementation for 64 bit reals:

int exp = (vu[F.EXPPOS_SHORT] & 0x7ff) - 0x3ff;
The constants are wrong: At least 0x7ff must be 0x7ff0.

(Remember, the 16 bits are s|eeeeeeeeeee|???? )

However, the results are still wrong and I don't really understand how
that equation should work.

The 'naive' and working way to write this is
--------
int exp = ((vu[F.EXPPOS_SHORT] & 0x7ff0) >> 4) -1023;
--------

I assume 0x3ff should be changed to 0x3ff0 which is 1023 << 4. But then
the result is still left-shifted by 4 and needs to be right-shifted:
-------
int exp = (((vu[F.EXPPOS_SHORT] & 0x7ff0)) - 0x3ff0) >> 4;
-------

is also working, but I don't know what's the advantage of this version.

floatTraits also has EXPBIAS = 0x3f_e_0? How was that value obtained?