[R] broken inline exp in glibc/x86??!
tlumley at u.washington.edu
Tue Jul 9 23:22:11 CEST 2002
On Tue, 9 Jul 2002, RenE J.V. Bertin wrote:
> I read the following in acinclude.m4:
> ## R_PROG_CC_FLAG_D__NO_MATH_INLINES
> ## ---------------------------
> ## In current glibc, inline version [x86] of exp is broken.
> ## We fix this by adding '-D__NO_MATH_INLINES' to R_XTRA_CFLAGS rather
> ## than AC_DEFINE(__NO_MATH_INLINES) as the former also takes care of
> ## compiling C code for add-on packages.
> Is this documented anywhere (where?), e.g. what is broken, which glibc
> versions are implicated, etc? If not, could anyone please tell me what
> is the matter -- I to use exp(), and I reckon that gcc will by default
> use the inline version!
I think that the problem was exp(-Inf) giving NaN rather than 0, but
trying to reproduce it with gcc 2.95.4 I can only make it happen with
-ffast-math, not with the -O flags. So it may be version-specific, or I
may have misremembered
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