Imported gcc-4.4.3

[msp430-gcc.git] / gmp / mpf / sqrt_ui.c

diff --git a/gmp/mpf/sqrt_ui.c b/gmp/mpf/sqrt_ui.c
new file mode 100644 (file)
index 0000000..17a3991
--- /dev/null
+++ b/gmp/mpf/sqrt_ui.c
@@ -0,0 +1,98 @@
+/* mpf_sqrt_ui -- Compute the square root of an unsigned integer.
+
+Copyright 1993, 1994, 1996, 2000, 2001, 2004, 2005 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 <stdio.h> /* for NULL */
+#include "gmp.h"
+#include "gmp-impl.h"
+
+
+/* As usual the aim is to produce PREC(r) limbs of result with the high limb
+   non-zero.  That high limb will end up floor(sqrt(u)), and limbs below are
+   produced by padding the input with zeros, two for each desired result
+   limb, being 2*(prec-1) for a total 2*prec-1 limbs passed to mpn_sqrtrem.
+   The way mpn_sqrtrem calculates floor(sqrt(x)) ensures the root is correct
+   to the intended accuracy, ie. truncated to prec limbs.
+
+   With nails, u might be two limbs, in which case a total 2*prec limbs is
+   passed to mpn_sqrtrem (still giving a prec limb result).  If uhigh is
+   zero we adjust back to 2*prec-1, since mpn_sqrtrem requires the high
+   non-zero.  2*prec limbs are always allocated, even when uhigh is zero, so
+   the store of uhigh can be done without a conditional.
+
+   u==0 is a special case so the rest of the code can assume the result is
+   non-zero (ie. will have a non-zero high limb on the result).
+
+   Not done:
+
+   No attempt is made to identify perfect squares.  It's considered this can
+   be left to an application if it might occur with any frequency.  As it
+   stands, mpn_sqrtrem does its normal amount of work on a perfect square
+   followed by zero limbs, though of course only an mpn_sqrtrem1 would be
+   actually needed.  We also end up leaving our mpf result with lots of low
+   trailing zeros, slowing down subsequent operations.
+
+   We're not aware of any optimizations that can be made using the fact the
+   input has lots of trailing zeros (apart from the perfect square
+   case).  */
+
+
+/* 1 if we (might) need two limbs for u */
+#define U2   (GMP_NUMB_BITS < BITS_PER_ULONG)
+
+void
+mpf_sqrt_ui (mpf_ptr r, unsigned long int u)
+{
+  mp_size_t rsize, zeros;
+  mp_ptr tp;
+  mp_size_t prec;
+  TMP_DECL;
+
+  if (UNLIKELY (u == 0))
+    {
+      r->_mp_size = 0;
+      r->_mp_exp = 0;
+      return;
+    }
+
+  TMP_MARK;
+
+  prec = r->_mp_prec;
+  zeros = 2 * prec - 2;
+  rsize = zeros + 1 + U2;
+
+  tp = (mp_ptr) TMP_ALLOC (rsize * BYTES_PER_MP_LIMB);
+
+  MPN_ZERO (tp, zeros);
+  tp[zeros] = u & GMP_NUMB_MASK;
+
+#if U2
+  {
+    mp_limb_t uhigh = u >> GMP_NUMB_BITS;
+    tp[zeros + 1] = uhigh;
+    rsize -= (uhigh == 0);
+  }
+#endif
+
+  mpn_sqrtrem (r->_mp_d, NULL, tp, rsize);
+
+  r->_mp_size = prec;
+  r->_mp_exp = 1;
+  TMP_FREE;
+}