Annotation of OpenXM_contrib/gmp/mpz/tstbit.c, Revision 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: }
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>