On Tue, 8 Feb 2022, Marco Bodrato wrote:
Ciao Marc,
Il 2022-01-22 23:40 Marc Glisse ha scritto:
the documentation for mpz_gcd_ui(rop, op1, op2) says "If rop is not
NULL, store the result there." and indeed the main code contains two
tests "if (w != NULL)". However, mpz_gcd_ui also contains special code
for the case where op2 (an unsigned long) does not fit in a limb. And
that code calls mpz_gcd without checking if the first argument is
NULL. That probably does not affect any platform, since nails are not
supported and I don't see anything defining __GMP_SHORT_LIMB.
What about the following (untested)?
Makes sense to me. I am just not sure if 3 is the right number and if we
are consistent about it. Shouldn't 2 be enough? Or is it to be safe in
case mpz_gcd decides to overallocate? 3 isn't a problem at all, but I
think a comment explaining it may avoid confusion in the future.
(replacing 2-3 with something larger would be up to a potential small-limb
branch)
I don't think we need to set SIZ(lw) but it looks cleaner and can't be
very expensive.
diff -r ed0406cf3c70 mpz/gcd_ui.c
--- a/mpz/gcd_ui.c Wed Feb 02 19:16:36 2022 +0100
+++ b/mpz/gcd_ui.c Tue Feb 08 09:30:53 2022 +0100
@@ -41,7 +41,16 @@
if (v > GMP_NUMB_MAX)
{
mpz_t vz;
- mp_limb_t vlimbs[2];
+ mpz_t lw;
+ mp_limb_t vlimbs[2], wlimbs[3];
+
+ if (w == NULL)
+ {
+ PTR(lw) = wlimbs;
+ ALLOC(lw) = 3;
+ SIZ(lw) = 0;
+ w = lw;
+ }
vlimbs[0] = v & GMP_NUMB_MASK;
vlimbs[1] = v >> GMP_NUMB_BITS;
PTR(vz) = vlimbs;
Ĝis,
m
--
Marc Glisse
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