Imported gcc-4.4.3

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

diff --git a/gmp/mpn/generic/sb_bdiv_qr.c b/gmp/mpn/generic/sb_bdiv_qr.c
new file mode 100644 (file)
index 0000000..d1cd0de
--- /dev/null
+++ b/gmp/mpn/generic/sb_bdiv_qr.c
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+/* mpn_sb_bdiv_qr -- schoolbook Hensel division with precomputed inverse,
+   returning quotient and remainder.
+
+   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.
+
+Copyright 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 a binary quotient of size qn = nn - dn.
+   Output:
+
+      Q = N * D^{-1} mod B^qn,
+
+      R = (N - Q * D) * B^(-qn)
+
+   Stores the dn least significant limbs of R at {np + nn - dn, dn},
+   and returns the borrow from the subtraction N - Q*D.
+
+   D must be odd. dinv is (-D)^-1 mod B. */
+
+mp_limb_t
+mpn_sb_bdiv_qr (mp_ptr qp,
+               mp_ptr np, mp_size_t nn,
+               mp_srcptr dp, mp_size_t dn, mp_limb_t dinv)
+{
+  mp_size_t qn;
+  mp_size_t i;
+  mp_limb_t rh;
+  mp_limb_t ql;
+
+  ASSERT (nn > 0);
+  ASSERT (dn > 0);
+  ASSERT (nn > dn);
+  ASSERT (dp[0] & 1);
+
+  qn = nn - dn;
+
+  rh = 0;
+
+  /* To complete the negation, this value is added to q. */
+  ql = 1;
+  while (qn > dn)
+    {
+      for (i = 0; i < dn; i++)
+       {
+         mp_limb_t q;
+
+         q = dinv * np[i];
+         qp[i] = ~q;
+
+         np[i] = mpn_addmul_1 (np + i, dp, dn, q);
+       }
+      rh += mpn_add (np + dn, np + dn, qn, np, dn);
+      ql = mpn_add_1 (qp, qp, dn, ql);
+
+      qp += dn; qn -= dn;
+      np += dn; nn -= dn;
+    }
+
+  for (i = 0; i < qn; i++)
+    {
+      mp_limb_t q;
+
+      q = dinv * np[i];
+      qp[i] = ~q;
+
+      np[i] = mpn_addmul_1 (np + i, dp, dn, q);
+    }
+
+  rh += mpn_add_n (np + dn, np + dn, np, qn);
+  ql = mpn_add_1 (qp, qp, qn, ql);
+
+  if (UNLIKELY (ql > 0))
+    {
+      /* q == 0 */
+      ASSERT (rh == 0);
+      return 0;
+    }
+  else
+    {
+      mp_limb_t cy;
+
+      cy = mpn_sub_n (np + qn, np + qn, dp, dn);
+      ASSERT (cy >= rh);
+      return cy - rh;
+    }
+}