Ciao,
Il 2022-08-30 10:25 Vincent Lefevre ha scritto:
or even (mn == 0 check just above this code rules out |m| < 1)
mpz_set_ui (r, mpz_cmpabs_ui (m, 1));
I agree with this solution. Will you commit it?
Concerning this second solution, the GMP manual says:
-- Function: int mpz_cmpabs_ui (const mpz_t OP1, unsigned long int
OP2)
Compare the absolute values of OP1 and OP2. Return a positive
value if abs(OP1) > abs(OP2), zero if abs(OP1) = abs(OP2), or a
negative value if abs(OP1) < abs(OP2).
So if the mpz_cmpabs_ui implementation is changed so that it can
return a value larger than 1, you need to make sure to remember to
update the code.
I propose to also add a couple of tests to mini-gmp/tests/t-powm.c , to
keep track of this.
----8<------
diff -r b0d6b9f5807e mini-gmp/tests/t-powm.c
--- a/mini-gmp/tests/t-powm.c Sat Aug 20 18:44:17 2022 +0200
+++ b/mini-gmp/tests/t-powm.c Mon Sep 05 19:02:23 2022 +0200
@@ -53,6 +53,31 @@
abort ();
}
}
+
+ if (mpz_cmp_ui (res, 1) <= 0)
+ mpz_add_ui (res, res, 9);
+
+ mpz_set_ui (e, 0);
+ /* Test the case m^0 (mod m), expect 1 (m is greater than 1). */
+ mpz_powm (res, res, e, res);
+ if (mpz_cmp_ui (res, 1) != 0)
+ {
+ fprintf (stderr, "mpz_powm failed: b=m, e=0; 1 expected,\n");
+ dump ("m", res);
+ dump ("r", res);
+ abort ();
+ }
+
+ /* Now res is 1. */
+ /* Test the case 1^0 (mod 1), expect 0. */
+ mpz_powm (res, res, e, res);
+ if (mpz_size (res))
+ {
+ fprintf (stderr, "mpz_powm failed: b=1, e=0, m=1; 0
expected,\n");
+ dump ("r", res);
+ abort ();
+ }
+
mpz_clear (b);
mpz_clear (e);
mpz_clear (m);
----8<------
Ĝis,
m
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