Ciao,
Il 2020-09-21 18:16 t...@gmplib.org ha scritto:
overflow. The overflow detection flags some false positives, which is
by design.
But maybe we could avoid the false positive at least for the following
example:
#include <stdio.h>
#include "gmp.h"
int main (void)
{
mpz_t z;
mpz_init (z);
mpz_setbit (z, 0xffffffdf);
printf ("OK\n");
mpz_sub_ui (z, z, 123);
printf ("OK\n");
return 0;
}
We can avoid it simply moving the REALLOC after the branch.
This may save some allocations in many cases.
The proposed patch follows:
diff -r b851f9336a86 mpz/aors_ui.h
--- a/mpz/aors_ui.h Thu Sep 17 12:00:00 2020 +0200
+++ b/mpz/aors_ui.h Mon Sep 21 18:36:33 2020 +0200
@@ -86,21 +86,26 @@
abs_usize = ABS (usize);
- /* If not space for W (and possible carry), increase space. */
- wp = MPZ_REALLOC (w, abs_usize + 1);
-
- /* These must be after realloc (U may be the same as W). */
- up = PTR (u);
-
if (usize VARIATION_CMP 0)
{
mp_limb_t cy;
+
+ /* If not space for W (and possible carry), increase space. */
+ wp = MPZ_REALLOC (w, abs_usize + 1);
+ /* These must be after realloc (U may be the same as W). */
+ up = PTR (u);
+
cy = mpn_add_1 (wp, up, abs_usize, (mp_limb_t) vval);
wp[abs_usize] = cy;
wsize = VARIATION_NEG (abs_usize + cy);
}
else
{
+ /* If not space for W, increase space. */
+ wp = MPZ_REALLOC (w, abs_usize);
+ /* These must be after realloc (U may be the same as W). */
+ up = PTR (u);
+
/* The signs are different. Need exact comparison to determine
which operand to subtract from which. */
if (abs_usize == 1 && up[0] < vval)
Ĝis,
m
--
http://bodrato.it/papers/
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