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Annotation of OpenXM_contrib/gmp/mpfr/extract.c, Revision 1.1

1.1     ! ohara       1: /* mpfr_extract -- bit-extraction function for the binary splitting algorithm
        !             2:
        !             3: Copyright 2000, 2001, 2002 Free Software Foundation, Inc.
        !             4:
        !             5: This file is part of the MPFR Library.
        !             6:
        !             7: The MPFR Library is free software; you can redistribute it and/or modify
        !             8: it under the terms of the GNU Lesser General Public License as published by
        !             9: the Free Software Foundation; either version 2.1 of the License, or (at your
        !            10: option) any later version.
        !            11:
        !            12: The MPFR Library is distributed in the hope that it will be useful, but
        !            13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
        !            15: License for more details.
        !            16:
        !            17: You should have received a copy of the GNU Lesser General Public License
        !            18: along with the MPFR Library; see the file COPYING.LIB.  If not, write to
        !            19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            20: MA 02111-1307, USA. */
        !            21:
        !            22: #include "gmp.h"
        !            23: #include "gmp-impl.h"
        !            24: #include "mpfr.h"
        !            25: #include "mpfr-impl.h"
        !            26:
        !            27: /* given 0 <= |p| < 1, this function extracts limbs of p and puts them in y.
        !            28:    It is mainly designed for the "binary splitting" algorithm together with
        !            29:    generic.c.
        !            30:
        !            31:    More precisely, if B = 2^BITS_PER_MP_LIMB:
        !            32:    - for i=0, y = floor(p * B)
        !            33:    - for i>0, y = (p * B^(2^i)) mod B^(2^(i-1))
        !            34:  */
        !            35:
        !            36: void
        !            37: mpfr_extract (mpz_ptr y, mpfr_srcptr p, unsigned int i)
        !            38: {
        !            39:   int two_i = 1 << i;
        !            40:   int two_i_2 = i ? two_i / 2 : 1;
        !            41:   mp_size_t size_p = MPFR_ABSSIZE(p);
        !            42:
        !            43:   /* as 0 <= |p| < 1, we don't have to care with infinities, NaN, ... */
        !            44:
        !            45:   _mpz_realloc (y, two_i_2);
        !            46:   if (size_p < two_i)
        !            47:     {
        !            48:       MPN_ZERO (PTR(y), two_i_2);
        !            49:       if (size_p >= two_i_2)
        !            50:         MPN_COPY (PTR(y) + two_i - size_p, MPFR_MANT(p), size_p - two_i_2);
        !            51:     }
        !            52:   else
        !            53:     MPN_COPY (PTR(y), MPFR_MANT(p) + size_p - two_i, two_i_2);
        !            54:
        !            55:   MPN_NORMALIZE (PTR(y), two_i_2);
        !            56:   SIZ(y) = (MPFR_ISNEG(p)) ? -two_i_2 : two_i_2;
        !            57: }