Em qua., 3 de jul. de 2024 às 08:18, Dean Rasheed <dean.a.rash...@gmail.com> escreveu:
> On Tue, 2 Jul 2024 at 21:10, Joel Jacobson <j...@compiler.org> wrote: > > > > I found the bug in the case 3 code, > > and it turns out the same type of bug also exists in the case 2 code: > > > > case 2: > > newdig = (int) var1digits[1] * > var2digits[res_ndigits - 4]; > > > > The problem here is that res_ndigits could become less than 4, > > Yes. It can't be less than 3 though (per an earlier test), so the case > 2 code was correct. > > I've been hacking on this a bit and trying to tidy it up. Firstly, I > moved it to a separate function, because it was starting to look messy > having so much extra code in mul_var(). Then I added a bunch more > comments to explain what's going on, and the limits of the various > variables. Note that most of the boundary checks are actually > unnecessary -- in particular all the ones in or after the main loop, > provided you pull out the first 2 result digits from the main loop in > the 3-digit case. That does seem to work very well, but... > > I wasn't entirely happy with how messy that code is getting, so I > tried a different approach. Similar to div_var_int(), I tried writing > a mul_var_int() function instead. This can be used for 1 and 2 digit > factors, and we could add a similar mul_var_int64() function on > platforms with 128-bit integers. The code looks quite a lot neater, so > it's probably less likely to contain bugs (though I have just written > it in a hurry,so it might still have bugs). In testing, it seemed to > give a decent speedup, but perhaps a little less than before. But > that's to be balanced against having more maintainable code, and also > a function that might be useful elsewhere in numeric.c. > > Anyway, here are both patches for comparison. I'll stop hacking for a > while and let you see what you make of these. > I liked v5-add-mul_var_int.patch better. I think that *var_digits can be const too. + const NumericDigit *var_digits = var->digits; Typo In the comments: - by procssing + by processing best regards, Ranier Vilela
