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/* mpfr_extract -- bit-extraction function for the binary splitting algorithm
Copyright (C) 2000 Free Software Foundation.
This file is part of the MPFR Library.
The MPFR 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 MPFR 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 MPFR 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 "mpfr.h"
#include "mpfr-impl.h"
#include "gmp-impl.h"
/* given 0 <= |p| < 1, this function extracts limbs of p and puts them in y.
It is mainly designed for the "binary splitting" algorithm together with
generic.c.
More precisely, if B = 2^BITS_PER_MP_LIMB:
- for i=0, y = floor(p * B)
- for i>0, y = (p * B^(2^i)) mod B^(2^(i-1))
*/
void
#if __STDC__
mpfr_extract (mpz_ptr y, mpfr_srcptr p, unsigned int i)
#else
mpfr_extract (y, p, i)
mpz_ptr y;
mpfr_srcptr p;
unsigned int i;
#endif
{
int two_i = 1 << i;
int two_i_2 = i ? two_i / 2 : 1;
mp_size_t size_p = MPFR_ABSSIZE(p);
/* as 0 <= |p| < 1, we don't have to care with infinities, NaN, ... */
_mpz_realloc (y, two_i_2);
if (size_p < two_i) {
MPN_ZERO (PTR(y), two_i_2);
if (size_p >= two_i_2)
MPN_COPY (PTR(y) + two_i - size_p, MPFR_MANT(p), size_p - two_i_2);
}
else
MPN_COPY (PTR(y), MPFR_MANT(p) + size_p - two_i, two_i_2);
MPN_NORMALIZE (PTR(y), two_i_2);
SIZ(y) = (MPFR_ISNEG(p)) ? -two_i_2 : two_i_2;
}
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