| /* mpfr_extract -- bit-extraction function for the binary splitting algorithm |
| |
| Copyright 2000, 2001, 2002, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc. |
| Contributed by the Arenaire and Cacao 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 2.1 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.LIB. If not, 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^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 |
| 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); |
| |
| /* as 0 <= |p| < 1, we don't have to care with infinities, NaN, ... */ |
| MPFR_ASSERTD (!MPFR_IS_SINGULAR (p)); |
| |
| _mpz_realloc (y, two_i_2); |
| if ((mpfr_uexp_t) size_p < two_i) |
| { |
| MPN_ZERO (PTR(y), two_i_2); |
| if ((mpfr_uexp_t) 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)) ? -two_i_2 : two_i_2; |
| } |