[Gmp-commit] /var/hg/gmp: 2 new changesets

[mercurial at gmplib.org]

details:   /var/hg/gmp/rev/1f8a8fefb5c2
changeset: 17631:1f8a8fefb5c2
user:      Marco Bodrato <bodrato at mail.dm.unipi.it>
date:      Mon May 28 06:22:20 2018 +0200
description:
tests/mpz/t-gcd_ui.c (check_ui_factors): New check triggering a possible bug.

details:   /var/hg/gmp/rev/e4849ae7c974
changeset: 17632:e4849ae7c974
user:      Marco Bodrato <bodrato at mail.dm.unipi.it>
date:      Mon May 28 06:24:27 2018 +0200
description:
mpn/generic/gcd_1.c: Avoid an undefined behaviour

diffstat:

 mpn/generic/gcd_1.c  |   2 +-
 tests/mpz/t-gcd_ui.c |  94 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+), 1 deletions(-)

diffs (122 lines):

diff -r aab8a010d10f -r e4849ae7c974 mpn/generic/gcd_1.c
--- a/mpn/generic/gcd_1.c	Mon May 21 00:13:27 2018 +0200
+++ b/mpn/generic/gcd_1.c	Mon May 28 06:24:27 2018 +0200
@@ -184,7 +184,7 @@
 	}
       count_trailing_zeros (c, t);
 #endif
-      ulimb >>= (c + 1);
+      ulimb = (ulimb >> c) >> 1;
     }
 
   vlimb = (vlimb << 1) | 1;
diff -r aab8a010d10f -r e4849ae7c974 tests/mpz/t-gcd_ui.c
--- a/tests/mpz/t-gcd_ui.c	Mon May 21 00:13:27 2018 +0200
+++ b/tests/mpz/t-gcd_ui.c	Mon May 28 06:24:27 2018 +0200
@@ -50,12 +50,106 @@
   mpz_clear (x);
 }
 
+static void
+check_ui_factors (void)
+{
+#define NUM_FACTORS 9
+  static const char* factors[NUM_FACTORS] = {
+    "641", "274177", "3", "5", "17", "257", "65537",
+    "59649589127497217", "1238926361552897" };
+  unsigned long  got;
+  mpz_t  x, b, d, f, g;
+  int  i, j;
+  gmp_randstate_ptr rands;
+
+  if (GMP_NUMB_BITS < 5 || GMP_NUMB_BITS == 8
+      || GMP_NUMB_BITS == 16 || GMP_NUMB_BITS > 511)
+    {
+      printf ("No usable factors for 2^%i+1.\n", GMP_NUMB_BITS);
+      return;
+    }
+
+  mpz_init (x);
+  mpz_init (d);
+  mpz_init (f);
+  mpz_init (g);
+
+  mpz_setbit (x, GMP_NUMB_BITS);
+  mpz_add_ui (x, x, 1);
+
+  for (i = 0; i < NUM_FACTORS; ++i)
+    {
+      mpz_set_str (f, factors[i], 10);
+      if (mpz_divisible_p (x, f))
+	{
+	  mpz_mul_2exp (f, f, 1);
+	  /* d is an odd multiple of the factor f, exactly filling a limb. */
+	  mpz_sub (d, x, f);
+	  /* f = 2^GMP_NUMB_BITS mod d. */
+	  mpz_sub_ui (f, f, 1);
+	  break;
+	}
+    }
+
+  mpz_gcd (g, f, d);
+  if (mpz_even_p (d) || mpz_cmp (d, f) <= 0 || mpz_cmp_ui (g, 1) != 0)
+    {
+      printf ("No usable factor found.\n");
+      abort ();
+    }
+
+  rands = RANDS;
+  mpz_mul_ui (x, d, gmp_urandomm_ui (rands, 30000) + 1);
+
+  mpz_init (b);
+  mpz_setbit (b, GMP_NUMB_BITS - 1);
+  for (j = 0; j < 4; ++j)
+    {
+      mpz_add (x, x, b);
+
+      for (i = 1; i >= -1; --i)
+	{
+	  if (mpz_fits_ulong_p (d)
+	      && ((got = mpz_gcd_ui (NULL, x, mpz_get_ui (d)))
+		  != (i != 0 ? 1 : mpz_get_ui (d))))
+	    {
+	      printf ("mpz_gcd_ui (f, kV+%i*2^%i, V): error (j = %i)\n", i, GMP_NUMB_BITS - 1, j);
+	      printf ("   return %#lx\n", got);
+	      printf ("   should be %#lx\n", (i != 0 ? 1 : mpz_get_ui (d)));
+	      abort ();
+	    }
+
+	  mpz_gcd (g, x, d);
+	  if ((mpz_cmp_ui (g, 1) == 0) != (i != 0))
+	    {
+	      printf ("mpz_gcd (f, kV+%i*2^%i, V): error (j = %i)\n", i, GMP_NUMB_BITS - 1, j);
+	      printf ("   should%s be one.\n",(i != 0 ? "" : " not"));
+	      abort ();
+	    }
+
+	  mpz_sub (x, x, b);
+	}
+      /* Back to the original x. */
+      mpz_addmul_ui (x, b, 2);
+      mpz_mul (b, b, f);
+      mpz_mod (b, b, d);
+    }
+
+  mpz_clear (g);
+  mpz_clear (x);
+  mpz_clear (f);
+  mpz_clear (d);
+  mpz_clear (b);
+}
+
+
 int
 main (void)
 {
   tests_start ();
 
   check_ui_range ();
+  check_ui_factors ();
 
   tests_end ();
   exit (0);