Re: mpz_gcd_ui(NULL, ...) with small limbs
Ciao Marc,
Il 2022-02-08 10:05 Marc Glisse ha scritto:
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
You are right. 2 should be enough.
I think that if a not realloc-able mpz is used as a target for a
function, it should contain at least one extra limb. But we are not
consistent about this.
If ones try
gmp$ grep MPZ_TMP_INIT -r mpz
many +1 are found...
But specifically for the gcd one can find
gmp$ grep MPZ_TMP_INIT -r mpq/aors.c
MPZ_TMP_INIT (gcd, MIN (op1_den_size, op2_den_size));
I don't think we need to set SIZ(lw) but it looks cleaner and can't be
very expensive.
I agree, not really needed, but it's probably better to always pass a
well defined mpz_t to functions.
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
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Re: mpz_gcd_ui(NULL, ...) with small limbs
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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Re: mpz_gcd_ui(NULL, ...) with small limbs
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)?
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
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Re: mpz_gcd_ui(NULL, ...) with small limbs
Ciao, Il Sab, 22 Gennaio 2022 11:40 pm, Marc Glisse ha scritto: > 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 Keeping unused code error-free is not easy, because it is not tested... But I think we should always correct it, when we run into a possible issue. The alternative, IMO, is to remove the unused_and_incorrect code. Yet another 2-limbs array, and dummy allocation are needed, I believe. Ĝis, m ___ gmp-bugs mailing list gmp-bugs@gmplib.org https://gmplib.org/mailman/listinfo/gmp-bugs
