[project @ 1998-06-05 14:37:59 by simonm]

[ghc-hetmet.git] / ghc / rts / gmp / mpz / clrbit.c

diff --git a/ghc/rts/gmp/mpz/clrbit.c b/ghc/rts/gmp/mpz/clrbit.c
new file mode 100644 (file)
index 0000000..59d9565
--- /dev/null
+++ b/ghc/rts/gmp/mpz/clrbit.c
@@ -0,0 +1,114 @@
+/* mpz_clrbit -- clear a specified bit.
+
+Copyright (C) 1991, 1993, 1994, 1995 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 Library General Public License as published by
+the Free Software Foundation; either version 2 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 Library General Public
+License for more details.
+
+You should have received a copy of the GNU Library General Public License
+along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+void
+#if __STDC__
+mpz_clrbit (mpz_ptr d, unsigned long int bit_index)
+#else
+mpz_clrbit (d, bit_index)
+     mpz_ptr d;
+     unsigned long int bit_index;
+#endif
+{
+  mp_size_t dsize = d->_mp_size;
+  mp_ptr dp = d->_mp_d;
+  mp_size_t limb_index;
+
+  limb_index = bit_index / BITS_PER_MP_LIMB;
+  if (dsize >= 0)
+    {
+      if (limb_index < dsize)
+       {
+         dp[limb_index] &= ~((mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB));
+         MPN_NORMALIZE (dp, dsize);
+         d->_mp_size = dsize;
+       }
+      else
+       ;
+    }
+  else
+    {
+      mp_size_t zero_bound;
+
+      /* Simulate two's complement arithmetic, i.e. simulate
+        1. Set OP = ~(OP - 1) [with infinitely many leading ones].
+        2. clear the bit.
+        3. Set OP = ~OP + 1.  */
+
+      dsize = -dsize;
+
+      /* No upper bound on this loop, we're sure there's a non-zero limb
+        sooner ot later.  */
+      for (zero_bound = 0; ; zero_bound++)
+       if (dp[zero_bound] != 0)
+         break;
+
+      if (limb_index > zero_bound)
+       {
+         if (limb_index < dsize)
+           dp[limb_index] |= (mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB);
+         else
+           {
+             /* Ugh.  The bit should be cleared outside of the end of the
+                number.  We have to increase the size of the number.  */
+             if (d->_mp_alloc < limb_index + 1)
+               {
+                 _mpz_realloc (d, limb_index + 1);
+                 dp = d->_mp_d;
+               }
+             MPN_ZERO (dp + dsize, limb_index - dsize);
+             dp[limb_index] = (mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB);
+             d->_mp_size = -(limb_index + 1);
+           }
+       }
+      else if (limb_index == zero_bound)
+       {
+         dp[limb_index] = ((dp[limb_index] - 1)
+                           | ((mp_limb_t) 1 << (bit_index % BITS_PER_MP_LIMB))) + 1;
+         if (dp[limb_index] == 0)
+           {
+             mp_size_t i;
+             for (i = limb_index + 1; i < dsize; i++)
+               {
+                 dp[i] += 1;
+                 if (dp[i] != 0)
+                   goto fin;
+               }
+             /* We got carry all way out beyond the end of D.  Increase
+                its size (and allocation if necessary).  */
+             dsize++;
+             if (d->_mp_alloc < dsize)
+               {
+                 _mpz_realloc (d, dsize);
+                 dp = d->_mp_d;
+               }
+             dp[i] = 1;
+             d->_mp_size = -dsize;
+           fin:;
+           }
+       }
+      else
+       ;
+    }
+}