Imported gcc-4.4.3

[msp430-gcc.git] / gmp / mpn / generic / sb_bdiv_q.c

diff --git a/gmp/mpn/generic/sb_bdiv_q.c b/gmp/mpn/generic/sb_bdiv_q.c
new file mode 100644 (file)
index 0000000..474c804
--- /dev/null
+++ b/gmp/mpn/generic/sb_bdiv_q.c
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+/* mpn_sb_bdiv_q -- schoolbook Hensel division with precomputed inverse,
+   returning quotient only.
+
+   Contributed to the GNU project by Niels Möller.
+
+   THE FUNCTIONS IN THIS FILE ARE INTERNAL FUNCTIONS WITH MUTABLE INTERFACES.
+   IT IS ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS
+   ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE.
+
+Copyright 2005, 2006 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 3 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.  If not, see http://www.gnu.org/licenses/.  */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+
+/* Computes Q = N / D mod B^nn, destroys N.
+   Clobbers N.
+
+   D must be odd. dinv is (-D)^-1 mod B.
+
+
+   The straightforward way to compute Q is to cancel one limb at a time, using
+
+     qp[i] = D^{-1} * np[i] (mod B)
+     N -= B^i * qp[i] * D
+
+   But we prefer addition to subtraction, since mpn_addmul_1 is often faster
+   than mpn_submul_1.  Q = - N / D can be computed by iterating
+
+     qp[i] = (-D)^{-1} * np[i] (mod B)
+     N += B^i * qp[i] * D
+
+   And then we flip the sign, -Q = (not Q) + 1.
+*/
+
+void
+mpn_sb_bdiv_q (mp_ptr qp,
+              mp_ptr np, mp_size_t nn,
+              mp_srcptr dp, mp_size_t dn,
+              mp_limb_t dinv)
+{
+  mp_size_t i;
+  mp_limb_t qh;
+
+  ASSERT (nn > 0);
+  ASSERT (dn > 0);
+  ASSERT (nn >= dn);
+  ASSERT (dp[0] & 1);
+
+  for (i = 0; i < nn - dn; i++)
+    {
+      mp_limb_t cy;
+      mp_limb_t q;
+
+      q = dinv * np[i];
+      qp[i] = ~q;
+      cy = mpn_addmul_1 (np + i, dp, dn, q);
+      mpn_add_1 (np + i + dn, np + i + dn, nn - i - dn, cy);
+      ASSERT (np[i] == 0);
+    }
+
+  for (; i < nn - 1; i++)
+    {
+      mp_limb_t q;
+
+      q = dinv * np[i];
+      qp[i] = ~q;
+      mpn_addmul_1 (np + i, dp, nn - i, q);
+
+      ASSERT (np[i] == 0);
+    }
+
+  /* Final limb */
+  qp[nn - 1] = ~(dinv * np[nn - 1]);
+  qh = mpn_add_1 (qp, qp, nn, 1); /* FIXME: can we get carry? */
+}