A 32bit/64bit performance data point

[Bill Allombert <allomber@math.u-bordeaux.fr>]

Hello Debian-amd64,

When porting PARI/GP, I have made some random benchmarks of 32bit vs
64bit on amd64 that you might find useful.

Here the results (on ravel, Opteron 1333MHz):

       |32bit+asm  32bit    64bit+asm 64bit
-----------------------------------------------------
general|  463        800     380       530
factor |11661      26491    4836      9723

The +asm versions are build with inline assembly code, the other are in
pure C.  The 'factor' bench use heavily multiprecision where 64bit
integers are useful.

So thoses computational tasks, 64bit is faster than 32bit probably 
thanks to the extra registers. 

Also amd64 is the only 64bit extension I know that have a hardware
64bitx64bit-to-128bit multiplication. Running this bench on sparc64
or hppa64 give inverse results, the 32bit version being always faster.

Cheers,
-- 
Bill. <ballombe@debian.org>

Imagine a large red swirl here.