Imported gcc-4.4.3

[msp430-gcc.git] / gmp / mpz / tstbit.c

diff --git a/gmp/mpz/tstbit.c b/gmp/mpz/tstbit.c
new file mode 100644 (file)
index 0000000..37f1454
--- /dev/null
+++ b/gmp/mpz/tstbit.c
@@ -0,0 +1,70 @@
+/* mpz_tstbit -- test a specified bit.
+
+Copyright 2000, 2002 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"
+
+
+/* For negatives the effective twos complement is achieved by negating the
+   limb tested, either with a ones or twos complement.  Twos complement
+   ("-") is used if there's only zero limbs below the one being tested.
+   Ones complement ("~") is used if there's a non-zero below.  Note that "-"
+   is correct even if the limb examined is 0 (and the true beginning of twos
+   complement is further up).
+
+   Testing the limbs below p is unavoidable on negatives, but will usually
+   need to examine only *(p-1).  The search is done from *(p-1) down to
+   *u_ptr, since that might give better cache locality, and because a
+   non-zero limb is perhaps a touch more likely in the middle of a number
+   than at the low end.
+
+   Bits past the end of available data simply follow sign of u.  Notice that
+   the limb_index >= abs_size test covers u=0 too.  */
+
+int
+mpz_tstbit (mpz_srcptr u, unsigned long bit_index)
+{
+  mp_srcptr      u_ptr      = PTR(u);
+  mp_size_t      size       = SIZ(u);
+  unsigned       abs_size   = ABS(size);
+  unsigned long  limb_index = bit_index / GMP_NUMB_BITS;
+  mp_srcptr      p          = u_ptr + limb_index;
+  mp_limb_t      limb;
+
+  if (limb_index >= abs_size)
+    return (size < 0);
+
+  limb = *p;
+  if (size < 0)
+    {
+      limb = -limb;     /* twos complement */
+
+      while (p != u_ptr)
+        {
+          p--;
+          if (*p != 0)
+            {
+              limb--;   /* make it a ones complement instead */
+              break;
+            }
+        }
+    }
+
+  return (limb >> (bit_index % GMP_NUMB_BITS)) & 1;
+}