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: }
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>