mirror of https://github.com/macssh/macssh.git
71 lines
1.9 KiB
C
Executable File
71 lines
1.9 KiB
C
Executable File
/* mpz_tstbit -- test a specified bit. Simulate 2's complement representation.
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Copyright (C) 1997 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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int
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#if __STDC__
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mpz_tstbit (mpz_srcptr d, unsigned long int bit_index)
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#else
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mpz_tstbit (d, bit_index)
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mpz_srcptr d;
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unsigned long int bit_index;
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#endif
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{
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mp_size_t dsize = d->_mp_size;
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mp_ptr dp = d->_mp_d;
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mp_size_t limb_index;
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limb_index = bit_index / BITS_PER_MP_LIMB;
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if (dsize >= 0)
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{
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if (limb_index < dsize)
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return (dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
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else
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/* Testing a bit outside of a positive number. */
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return 0;
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}
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else
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{
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mp_size_t zero_bound;
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dsize = -dsize;
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/* Locate the least significant non-zero limb. */
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for (zero_bound = 0; dp[zero_bound] == 0; zero_bound++)
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;
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if (limb_index > zero_bound)
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{
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if (limb_index < dsize)
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return (~dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
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else
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/* Testing a bit outside of a negative number. */
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return 1;
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}
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else if (limb_index == zero_bound)
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return (-dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
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else
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return 0;
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}
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}
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