Re: [ccp4bb]: CCP4 installation on Irix notes

[kay <kay.diederichs@uni-konstanz.de>]

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"David J. Schuller" wrote:
> 
> On Fri, 16 Mar 2001, Kay Diederichs wrote:
> 
> > I would like to make two points about CCP4 installation on Irix.
> > 1) the -n32 ABI has a number of advantages compared to the (old and CCP4
> > default) -o32 (or -32, which is the same) ABI.
> > This runs without problems here (Irix 6.5 and compiler 7.3.1.2m), and is
> > 50-100% faster than -o32.
> 
> you do not describe the hardware you are running on.  the -n32 is
> optimised for the R10000 instruction set.  The reason the -32 option is
> still used is that it uses the R4000 instruction set, which is essential
> for those of us with older hardware(R4000, R4400).
> 

-n32 works on R4x00, R5x00, R8000 and R1x000 chips. What you describe as
a problem with older hardware is an issue of -mips4 (which is supported
by R5x00 and up, but not on R4x00) versus -mips3 . 

-mips4 is the compiler default if you compile on R1x000; so if you want
to make sure your R1x000 - compiled binaries work also on R4x00 then you
should change the compiler default (in /etc/compiler.defaults ) or
manually add -mips3 to the compilation flags (just adapt the recipe I
posted). The gain in speed of -mips4 over -mips3 is - on average - on
the order of a few percent.

-mips3 versus -mips4 is not an issue for the -o32 compiler because it
supports neither of them (it produces mips2 or mips1 binaries) - that's
also one of the reasons why the binaries it produces run slower than the
-n32 binaries. This is covered in the ABI manpage on Irix systems.

To add to my previous posting: it is a common misunderstanding that -64
is required on IRIX64 machines (Octane, Origin), or runs faster than
-n32 on these machines. -64 is only required for programs with array
sizes > 1.8GB (-n32 can address 2GB but the system libraries occupy some
of this) , and I doubt that many crystallographic problems need that!

Summary: -n32 -mips3 will work well on all current SGI hardware, from an
old Indy up to a 128-processor Origin 3000.

Kay
-- 
Kay Diederichs                    
email: Kay.Diederichs@uni-konstanz.de   Tel: +49 7531 88 4049  Fax: 3183
Fakultät für Biologie, M656, Universität Konstanz, D-78457 Konstanz