1 /* mpfr_extract -- bit-extraction function for the binary splitting algorithm 2 3 Copyright 2000, 2001, 2002, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc. 4 Contributed by the Arenaire and Caramel projects, INRIA. 5 6 This file is part of the GNU MPFR Library. 7 8 The GNU MPFR Library is free software; you can redistribute it and/or modify 9 it under the terms of the GNU Lesser General Public License as published by 10 the Free Software Foundation; either version 3 of the License, or (at your 11 option) any later version. 12 13 The GNU MPFR Library is distributed in the hope that it will be useful, but 14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16 License for more details. 17 18 You should have received a copy of the GNU Lesser General Public License 19 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 22 23 #include "mpfr-impl.h" 24 25 /* given 0 <= |p| < 1, this function extracts limbs of p and puts them in y. 26 It is mainly designed for the "binary splitting" algorithm. 27 28 More precisely, if B = 2^GMP_NUMB_BITS: 29 - for i=0, y = floor(p * B) 30 - for i>0, y = (p * B^(2^i)) mod B^(2^(i-1)) 31 */ 32 33 void 34 mpfr_extract (mpz_ptr y, mpfr_srcptr p, unsigned int i) 35 { 36 unsigned long two_i = 1UL << i; 37 unsigned long two_i_2 = i ? two_i / 2 : 1; 38 mp_size_t size_p = MPFR_LIMB_SIZE (p); 39 40 /* as 0 <= |p| < 1, we don't have to care with infinities, NaN, ... */ 41 MPFR_ASSERTD (!MPFR_IS_SINGULAR (p)); 42 43 _mpz_realloc (y, two_i_2); 44 if ((mpfr_uexp_t) size_p < two_i) 45 { 46 MPN_ZERO (PTR(y), two_i_2); 47 if ((mpfr_uexp_t) size_p >= two_i_2) 48 MPN_COPY (PTR(y) + two_i - size_p, MPFR_MANT(p), size_p - two_i_2); 49 } 50 else 51 MPN_COPY (PTR(y), MPFR_MANT(p) + size_p - two_i, two_i_2); 52 53 MPN_NORMALIZE (PTR(y), two_i_2); 54 SIZ(y) = (MPFR_IS_NEG (p)) ? -two_i_2 : two_i_2; 55 } 56