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/* mpz_tstbit -- test a specified bit. Simulate 2's complement representation.
Copyright (C) 1997 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"
int
#if __STDC__
mpz_tstbit (mpz_srcptr d, unsigned long int bit_index)
#else
mpz_tstbit (d, bit_index)
mpz_srcptr 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)
return (dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
else
/* Testing a bit outside of a positive number. */
return 0;
}
else
{
mp_size_t zero_bound;
dsize = -dsize;
/* Locate the least significant non-zero limb. */
for (zero_bound = 0; dp[zero_bound] == 0; zero_bound++)
;
if (limb_index > zero_bound)
{
if (limb_index < dsize)
return (~dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
else
/* Testing a bit outside of a negative number. */
return 1;
}
else if (limb_index == zero_bound)
return (-dp[limb_index] >> (bit_index % BITS_PER_MP_LIMB)) & 1;
else
return 0;
}
}
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