Imported gcc-4.4.3

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

diff --git a/gmp/mpn/generic/sb_divappr_q.c b/gmp/mpn/generic/sb_divappr_q.c
new file mode 100644 (file)
index 0000000..42a39be
--- /dev/null
+++ b/gmp/mpn/generic/sb_divappr_q.c
@@ -0,0 +1,136 @@
+/* mpn_sb_divappr_q -- schoolbook division with 2-limb sloppy non-greater
+   precomputed inverse, returning approximate quotient.
+
+   Contributed to the GNU project by Torbjörn Granlund.
+
+   THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH A MUTABLE INTERFACE.  IT IS
+   ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS
+   ALMOST GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GMP
+   RELEASE.
+
+Copyright 2006, 2007 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"
+#include "longlong.h"
+
+/*
+  CAVEATS:
+  1. Should it demand normalized operands like now, or normalize on-the-fly?
+  2. Overwrites {np,nn}.
+  3. Uses mpn_submul_1.  It would be nice to somehow make it use mpn_addmul_1
+     instead.  (That would open for mpn_addmul_2 straightforwardly.)
+*/
+
+mp_limb_t
+mpn_sb_divappr_q (mp_ptr qp,
+                 mp_ptr np, mp_size_t nn,
+                 mp_srcptr dp, mp_size_t dn,
+                 mp_srcptr dip)
+{
+  mp_limb_t q, q10, q01a, q00a, q01b, q00b;
+  mp_limb_t cy;
+  mp_size_t i;
+  mp_limb_t qh;
+  mp_limb_t di1, di0;
+  mp_size_t qn;
+
+  ASSERT (dn > 0);
+  ASSERT (nn >= dn);
+  ASSERT ((dp[dn-1] & GMP_NUMB_HIGHBIT) != 0);
+  ASSERT (! MPN_OVERLAP_P (np, nn, dp, dn));
+  ASSERT (! MPN_OVERLAP_P (qp, nn-dn, dp, dn));
+  ASSERT (! MPN_OVERLAP_P (qp, nn-dn, np, nn) || qp+dn >= np);
+  ASSERT_MPN (np, nn);
+  ASSERT_MPN (dp, dn);
+
+  np += nn;
+  qn = nn - dn;
+  if (qn + 1 < dn)
+    {
+      dp += dn - (qn + 1);
+      dn = qn + 1;
+    }
+
+  qh = mpn_cmp (np - dn, dp, dn) >= 0;
+  if (qh != 0)
+    mpn_sub_n (np - dn, np - dn, dp, dn);
+
+  qp += qn;
+  di1 = dip[1]; di0 = dip[0];
+  for (i = qn; i >= dn; i--)
+    {
+      np--;
+      umul_ppmm (q, q10, np[0], di1);
+      umul_ppmm (q01a, q00a, np[-1], di1);
+      add_ssaaaa (q, q10, q, q10, np[0], q01a);
+      umul_ppmm (q01b, q00b, np[0], di0);
+      add_ssaaaa (q, q10, q, q10, 0, q01b);
+      add_ssaaaa (q, q10, q, q10, 0, np[-1]);
+
+      cy = mpn_submul_1 (np - dn, dp, dn, q);
+
+      if (UNLIKELY (np[0] > cy || mpn_cmp (np - dn, dp, dn) >= 0))
+       {
+         q = q + 1;
+         mpn_sub_n (np - dn, np - dn, dp, dn);
+       }
+
+      *--qp = q;
+    }
+
+  for (i = dn - 1; i > 0; i--)
+    {
+      np--;
+      umul_ppmm (q, q10, np[0], di1);
+      umul_ppmm (q01a, q00a, np[-1], di1);
+      add_ssaaaa (q, q10, q, q10, np[0], q01a);
+      umul_ppmm (q01b, q00b, np[0], di0);
+      add_ssaaaa (q, q10, q, q10, 0, q01b);
+      add_ssaaaa (q, q10, q, q10, 0, np[-1]);
+
+      cy = mpn_submul_1 (np - dn, dp, dn, q);
+
+      if (UNLIKELY (np[0] > cy || mpn_cmp (np - dn, dp, dn) >= 0))
+       {
+         q = q + 1;
+         if (q == 0)
+           q = GMP_NUMB_MAX;
+         else
+           mpn_sub_n (np - dn, np - dn, dp, dn);
+       }
+
+      *--qp = q;
+
+      /* Truncate operands.  */
+      dn--;
+      dp++;
+
+      /* The partial remainder might be equal to the truncated divisor,
+        thus non-canonical.  When that happens, the rest of the quotient
+        should be all ones.  */
+      if (UNLIKELY (mpn_cmp (np - dn, dp, dn) == 0))
+       {
+         while (--i)
+           *--qp = GMP_NUMB_MAX;
+         break;
+       }
+    }
+
+  return qh;
+}