X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2Fgmp%2Fmpn%2Fgeneric%2Fjacbase.c;fp=rts%2Fgmp%2Fmpn%2Fgeneric%2Fjacbase.c;h=dd437f1ac1b5dd3524ed92b7c7edaff1f4c1f17b;hb=0065d5ab628975892cea1ec7303f968c3338cbe1;hp=0000000000000000000000000000000000000000;hpb=28a464a75e14cece5db40f2765a29348273ff2d2;p=ghc-hetmet.git

diff --git a/rts/gmp/mpn/generic/jacbase.c b/rts/gmp/mpn/generic/jacbase.c
new file mode 100644
index 0000000..dd437f1
--- /dev/null
+++ b/rts/gmp/mpn/generic/jacbase.c
@@ -0,0 +1,136 @@
+/* mpn_jacobi_base -- limb/limb Jacobi symbol with restricted arguments.
+
+   THIS INTERFACE IS PRELIMINARY AND MIGHT DISAPPEAR OR BE SUBJECT TO
+   INCOMPATIBLE CHANGES IN A FUTURE RELEASE OF GMP. */
+
+/*
+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 Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser 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"
+
+
+#if COUNT_TRAILING_ZEROS_TIME <= 7
+/* If count_trailing_zeros is fast, use it.
+   K7 at 7 cycles and P6 at 2 are good here.  K6 at 12-27 and P5 at 18-42
+   are not.  The default 15 in longlong.h is meant to mean not good here.  */
+
+#define PROCESS_TWOS_ANY                                \
+  {                                                     \
+    mp_limb_t  twos;                                    \
+    count_trailing_zeros (twos, a);                     \
+    result_bit1 ^= JACOBI_TWOS_U_BIT1 (twos, b);        \
+    a >>= twos;                                         \
+  }
+
+#define PROCESS_TWOS_EVEN  PROCESS_TWOS_ANY
+
+#else
+/* Use a loop instead.  With "a" uniformly distributed there will usually be
+   only a few trailing zeros.
+
+   Unfortunately the branch for the while loop here will be on a 50/50
+   chance of a 1 or 0, which is bad for branch prediction.  */
+
+#define PROCESS_TWOS_EVEN               \
+  {                                     \
+    int  two;                           \
+    two = JACOBI_TWO_U_BIT1 (b);        \
+    do                                  \
+      {                                 \
+        a >>= 1;                        \
+        result_bit1 ^= two;             \
+        ASSERT (a != 0);                \
+      }                                 \
+    while ((a & 1) == 0);               \
+  }
+
+#define PROCESS_TWOS_ANY        \
+  if ((a & 1) == 0)             \
+    PROCESS_TWOS_EVEN;
+
+#endif
+
+
+/* Calculate the value of the Jacobi symbol (a/b) of two mp_limb_t's, but
+   with a restricted range of inputs accepted, namely b>1, b odd, and a<=b.
+
+   The initial result_bit1 is taken as a parameter for the convenience of
+   mpz_kronecker_zi_ui() et al.  The sign changes both here and in those
+   routines accumulate nicely in bit 1, see the JACOBI macros.
+
+   The return value here is the normal +1, 0, or -1.  Note that +1 and -1
+   have bit 1 in the "BIT1" sense, which could be useful if the caller is
+   accumulating it into some extended calculation.
+
+   Duplicating the loop body to avoid the MP_LIMB_T_SWAP(a,b) would be
+   possible, but a couple of tests suggest it's not a significant speedup,
+   and may even be a slowdown, so what's here is good enough for now.
+
+   Future: The code doesn't demand a<=b actually, so maybe this could be
+   relaxed.  All the places this is used currently call with a<=b though.  */
+
+int
+#if __STDC__
+mpn_jacobi_base (mp_limb_t a, mp_limb_t b, int result_bit1)
+#else
+mpn_jacobi_base (a, b, result_bit1)
+     mp_limb_t a;
+     mp_limb_t b;
+     int       result_bit1;
+#endif
+{
+  ASSERT (b & 1);  /* b odd */
+  ASSERT (b != 1);
+  ASSERT (a <= b);
+
+  if (a == 0)
+    return 0;
+
+  PROCESS_TWOS_ANY;
+  if (a == 1)
+    goto done;
+
+  for (;;)
+    {
+      result_bit1 ^= JACOBI_RECIP_UU_BIT1 (a, b);
+      MP_LIMB_T_SWAP (a, b);
+
+      do
+	{
+          /* working on (a/b), a,b odd, a>=b */
+          ASSERT (a & 1);
+          ASSERT (b & 1);
+          ASSERT (a >= b);
+
+	  if ((a -= b) == 0)
+	    return 0;
+
+          PROCESS_TWOS_EVEN;
+	  if (a == 1)
+	    goto done;
+	}
+      while (a >= b);
+    }
+
+ done:
+  return JACOBI_BIT1_TO_PN (result_bit1);
+}