On 6/2/14, Mark Kettenis <[email protected]> wrote:
>> Date: Mon, 2 Jun 2014 10:17:53 +0200 (CEST)
>> From: Mark Kettenis <[email protected]>
>>
>> > Date: Mon, 02 Jun 2014 09:34:20 +0200
>> > From: Benjamin Baier <[email protected]>
>> >
>> > You might want to read up on floating point arithmetic. (rounding and
>> > representation)
>>
>> Well, the difference between 4.994404 and 5.0 is a bit large to blame
>> rounding and binary representation. And other OpenBSD platforms
>> (amd64, sparc64, powerpc) return the expected result. So I'd say that
>> there is a bug in the i386-specific implementation of exp2(3).
>
> And here is a fix. There actually isn't any i386-specific code, but
> i386 is "special" and needs STRICT_ALIGN() to work properly for double
> as well as float. FreeBSD made the same change a while ago:
>
> http://svnweb.FreeBSD.org/base/head/lib/msun/src/math_private.h?revision=240827&view=markup
You are quick. Thanks for figuring this out.
Ugh ... "it was intentionally left broken as an optimization". That's crazy.
OK martynas@.
> Haven't run the regression tests yet with this change.
>
>
> Index: src/math_private.h
> ===================================================================
> RCS file: /cvs/src/lib/libm/src/math_private.h,v
> retrieving revision 1.16
> diff -u -p -r1.16 math_private.h
> --- src/math_private.h 12 Nov 2013 20:35:09 -0000 1.16
> +++ src/math_private.h 2 Jun 2014 09:30:13 -0000
> @@ -349,7 +349,7 @@ do {
> \
> #define STRICT_ASSIGN(type, lval, rval) do { \
> volatile type __lval; \
> \
> - if (sizeof(type) >= sizeof(double)) \
> + if (sizeof(type) >= sizeof(long double)) \
> (lval) = (rval); \
> else { \
> __lval = (rval); \
>
