Re: [parisc-linux] uninline in bitops.c as ia64 or sparc64?

["Michael S. Zick" <mszick@goquest.com>]

On Mon August 9 2004 09:54, Michael S. Zick wrote:
>
-------
> 
> Mike
> 
> Index: include/asm-parisc/bitops.h
> ===================================================================
> RCS file: /opt/lib/cvs/parisc/include/asm-parisc/bitops.h,v
> retrieving revision 1.1.1.1
> diff -u -3 -p -r1.1.1.1 bitops.h
Sorry for the self-reply...

If compiled with 32-bit compiler the NOT(__LP64__) path will compile.
If the resultant program is loaded on a 64-bit machine running 'narrow mode';
it will fail.  Since the mode bit only changes the addressing not the 
bit-position numbering.(1)

Translation:
As submitted, it should compile for 64-bit and run 64-Wide;
it should compile for 32-bit and run 32-bit.
It is only the case of compiling for 32-bit and then trying to
run it on a 64-bit machine in narrow mode that should fail.

I'll work on this - I probably will abuse the shift-right-double
instruction to come up with a compiles correctly, runs anywhere
version.

Two other problems I am considering:

1) It only beats on two (not counting GR0) registers;
it will probably cause register stalls on pipelined machines.

2) It is bigger than a cache line, probably executes in less
than a memory cycle - so it will probably 'starve' the cpu;
waiting for the next memory cycle to fill the next i-cache line.

Taken all together - an interesting problem.

Mike
(1) Does 32-bit gcc ever generate extract/deposit? This might
cause problems running anything 32-bit on 64-bit-narrow.
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