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Annotation of OpenXM_contrib/gmp/mpz/tstbit.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpz_tstbit -- test a specified bit.  Simulate 2's complement representation.
                      2:
                      3: Copyright (C) 1997 Free Software Foundation, Inc.
                      4:
                      5: This file is part of the GNU MP Library.
                      6:
                      7: The GNU MP Library is free software; you can redistribute it and/or modify
                      8: it under the terms of the GNU Lesser General Public License as published by
                      9: the Free Software Foundation; either version 2.1 of the License, or (at your
                     10: option) any later version.
                     11:
                     12: The GNU MP Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Lesser General Public License
                     18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     20: MA 02111-1307, USA. */
                     21:
                     22: #include "gmp.h"
                     23: #include "gmp-impl.h"
                     24:
                     25: int
                     26: #if __STDC__
                     27: mpz_tstbit (mpz_srcptr d, unsigned long int bit_index)
                     28: #else
                     29: mpz_tstbit (d, bit_index)
                     30:      mpz_srcptr d;
                     31:      unsigned long int bit_index;
                     32: #endif
                     33: {
                     34:   mp_size_t dsize = d->_mp_size;
                     35:   mp_ptr dp = d->_mp_d;
                     36:   mp_size_t limb_index;
                     37:
                     38:   limb_index = bit_index / BITS_PER_MP_LIMB;
                     39:   if (dsize >= 0)
                     40:     {
                     41:       if (limb_index < dsize)
                     42:        return (dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
                     43:       else
                     44:        /* Testing a bit outside of a positive number.  */
                     45:        return 0;
                     46:     }
                     47:   else
                     48:     {
                     49:       mp_size_t zero_bound;
                     50:
                     51:       dsize = -dsize;
                     52:
                     53:       /* Locate the least significant non-zero limb.  */
                     54:       for (zero_bound = 0; dp[zero_bound] == 0; zero_bound++)
                     55:        ;
                     56:
                     57:       if (limb_index > zero_bound)
                     58:        {
                     59:          if (limb_index < dsize)
                     60:            return (~dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
                     61:          else
                     62:            /* Testing a bit outside of a negative number.  */
                     63:            return 1;
                     64:        }
                     65:       else if (limb_index == zero_bound)
                     66:        return (-dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
                     67:       else
                     68:        return 0;
                     69:     }
                     70: }