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[Bug target/37390] wrong-code on i486-linux-gnu with -O[12], -O0 works
- From: "vincent at vinc17 dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 6 Sep 2008 18:42:39 -0000
- Subject: [Bug target/37390] wrong-code on i486-linux-gnu with -O[12], -O0 works
- References: <bug-37390-11764@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #8 from vincent at vinc17 dot org 2008-09-06 18:42 -------
(In reply to comment #7)
> Does increasing bits cause floating point errors. How could 64 bit precison
> give correct result where as 80 bit give incorrect one.
You can have rounding errors whether you increase the precision or not. In
particular, in practice, function pow() is not correctly rounded, and worse,
the error may be quite high. So, I'd say that whatever the choice made by
Linux, your code may be regarded as wrong (and I think this bug is just
invalid, as you could have similar problems with SSE2).
> junk@edubuntu:~/prog/tju$ gcc -O2 -mfpmath=sse bug_short.c -lm
> bug_short.c:1: warning: SSE instruction set disabled, using 387 arithmetics
You probably need another compilation flag, like -march=pentium4.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37390