Mark Dickinson <[EMAIL PROTECTED]> added the comment: Thanks for the updated patch! Looks good, on a quick scan.
(One comment typo I noticed: there's a line BASE - 3 = 2*MASK - 1 presumably this should be 2*BASE - 3 on the LHS.) Just out of interest, is it possible to go further, and combine 4 partial multiplications at once instead of 2? Or does the extra bookkeeping involved make it not worth it? I think it's important to make sure that any changes to longobject.c don't slow down operations on small integers (where "small" means "less than 2**32") noticeably. Re: possible changes to PyLong_SHIFT Yes, changing PyLong_SHIFT to 16 (or 32) would be complicated, and would involve almost a complete rewrite of longobject.c, together with much else... It wasn't really a serious suggestion, but it probably would provide a speedup. The code in GMP gives some idea how things might work. Changing PyLong_SHIFT to 30 doesn't seem like a totally ridiculous idea, though. One problem is that there's no 64-bit integer type (for twodigits) in *standard* C89; so since Python is only allowed to assume C89 there would have to be some fallback code for those (very few, surely) platforms that didn't have a 64-bit integer type available. On 64-bit machines one could presumably go further, and have PyLong_SHIFT be 60 (or 62, or 63 --- but those break the assumption in long_pow that the PyLong_SHIFT is a multiple of 5). This would depend on the compiler providing a 128-bit type for twodigits (like __uint128_t on gcc/x86-64). Probably not worth it, especially if it ends up slowing down operations on everyday small integers. Any of these changes is also going to affect a good few other parts of the codebase (e.g. marshal, pickle?, struct?, floatobject.c, ...). It shouldn't be difficult to find most of the files affected (just look to see which files include longintrepr.h), but I have a suspicion there are a couple of other places that just assume PyLong_SHIFT is 15). _______________________________________ Python tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue3944> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
