* mpz/kronzu.c: New file.

1 files changed, 67 insertions, 0 deletions

diff --git a/mpz/kronzu.c b/mpz/kronzu.c
new file mode 100644
index 000000000..636afb36e
--- /dev/null
+++ b/mpz/kronzu.c
@@ -0,0 +1,67 @@
+/* mpz_kronecker_zi_ui -- Kronecker/Jacobi symbol. */
+
+/*
+Copyright (C) 1999, 2000 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Library General Public License as published by
+the Free Software Foundation; either version 2 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
+License for more details.
+
+You should have received a copy of the GNU Library General Public License
+along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA.
+*/
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+
+/* This function is expected to be often used with b an odd prime, so the
+   code for odd b is nice and short. */
+
+int
+#if __STDC__
+mpz_kronecker_zi_ui (mpz_srcptr a, unsigned long b)
+#else
+mpz_kronecker_zi_ui (a, b)
+     mpz_srcptr    a;
+     unsigned long b;
+#endif
+{
+  int  twos;
+
+  ASSERT (sizeof (mp_limb_t) >= sizeof (unsigned long));
+
+  if (b & 1)
+    {
+      if (b != 1)
+        return mpn_jacobi_base (mpz_fdiv_ui (a, b), b, 0);
+      else
+        return 1;  /* (a/1)=1 for any a */
+    }
+
+  if (b == 0)
+    return JACOBI_Z0 (a);
+
+  /* (a/2)=0 if a even */
+  if (mpz_even_p (a))
+    return 0;
+
+  /* (a/2)=(2/a) when a odd */
+  count_trailing_zeros (twos, b);  
+  if ((b >>= twos) == 1)
+    return JACOBI_TWOS_U (twos, PTR(a)[0]);
+
+  return mpn_jacobi_base (mpz_fdiv_ui (a, b), b,
+                          JACOBI_TWOS_U_BIT1(twos, PTR(a)[0]));
+}