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Re: [ccp4bb]: REFMAC5 under CCP4 4.1
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>>>>> "GM" == Garib Murshudov <email@example.com> writes:
GM> Here is very small program wich behaves differently with -O2
GM> (result 6 1) and -O0 (result 6 6). This type of code may be seen
That doesn't mean that it's good code. The g77 manual has discussion
and useful references about floating-point arithmetic, particularly
the perils of the x86 architecture and floating-point comparisons.
However, the result above does look like a code generation bug. The
`submodel' defaults with which the compiler was built (see the SPECS
file) could affect this unless you specify -mcpu and -march, at least.
Using -O0 can easily give you an order of magnitude speed hit, but
there are various handles to turn individual optimizations on and off.
GM> (red hat version 7.0, gcc 2.96 g77 0.5.24)
Damn RedHat. <URL:http://gcc.gnu.org/gcc-2.96.html> (and the last
released version of g77 was 0.5.25). Get a packaged version of GCC
2.95.2 or build it from scratch, which is easy.
[I recommend Debian GNU/Linux for various reasons, even though they
don't clearly label things in the distribution like GCC as somewhat
modified versions (sigh).]