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/* mpfr_extract -- bit-extraction function for the binary splitting algorithm
Copyright 2000-2002, 2004-2019 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.
The GNU 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 Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#include "mpfr-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.
More precisely, if B = 2^GMP_NUMB_BITS:
- for i=0, y = floor(p * B)
- for i>0, y = (p * B^(2^i)) mod B^(2^(i-1))
*/
void
mpfr_extract (mpz_ptr y, mpfr_srcptr p, unsigned int i)
{
unsigned long two_i = 1UL << i;
unsigned long two_i_2 = i ? two_i / 2 : 1;
mp_size_t size_p = MPFR_LIMB_SIZE (p);
MPFR_ASSERTN (two_i != 0 && two_i_2 <= INT_MAX); /* overflow check */
/* as 0 <= |p| < 1, we don't have to care with infinities, NaN, ... */
MPFR_ASSERTD (!MPFR_IS_SINGULAR (p));
mpz_realloc2 (y, (mp_bitcnt_t) two_i_2 * GMP_NUMB_BITS);
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_IS_NEG (p) ? - (int) two_i_2 : (int) two_i_2;
}
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