Hello, For readers of gmp-discuss and Daniel Schepler: this concerns a bug reported to Debian regarding GMP on the x32 architecture. In a nutshell: x32 selects a limb size of 8, which means it is larger than a pointer and some software (gap, pari) fail to build. The question is whether it makes sense to change the limb size to 4 on x32. I'd appreciate your thoughts.
See full thread at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=724320 Thanks, -Steve On September 24, 2013 10:54:11 PM Bill Allombert wrote: > On Mon, Sep 23, 2013 at 04:44:15PM -0500, Steve M. Robbins wrote: > > Bill, > > > > Thanks for clarifying the issue. > > > > On Mon, Sep 23, 2013 at 08:14:58PM +0200, Bill Allombert wrote: > > > Admittedly, this is a bug in pari and gap for having such requirement. > > > However, it seems unlikely to be ever fixed, hence this report. > > > > > > Using 8 should result in a faster library, so this is a trade-off, even > > > if I do not expect that people will use x32 for HPC. > > > > OK, so this trade-off is the real issue. What is the best choice? > > > > On the one hand, 8 should be faster but how much faster? Enough to > > matter? If not, the choice is clear: switch to 4. > > I suppose it will depend of the hardware. I do not know who will choose > to use x32 rather than x86_64. > If the purpose is to save memory, they it could be argued that using 4 is > better, since this saves 2 bytes on average for each GMP integers. > (e.g. Numbers < 2^32 are stored on 4 bytes instead of 8). > > > If the speed difference matters, then the question is whether pari and > > gap are important enough to x32 that we should accept the lower speed. > > I don't know, myself, but my gut instinct is to leave the size at 8 > > and exclude x32 from the architectures for pari and gap. > > Well, there might be other packages affected, I did not do a full search. > (It affects packages that uses the mpn class of functions) > The problem of excluding pari and gap is that this also excludes their > reverse dependencies. > > Alternatively, both version of ligmp-dev could be provided on x32. > > Cheers, > Bill.
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