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Annotation of OpenXM_contrib/gmp/mpfr/extract.c, Revision 1.1.1.1

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: }