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Annotation of OpenXM_contrib/gmp/mpf/div_2exp.c, Revision 1.1.1.3

1.1       maekawa     1: /* mpf_div_2exp -- Divide a float by 2^n.
                      2:
1.1.1.3 ! ohara       3: Copyright 1993, 1994, 1996, 2000, 2001, 2002 Free Software Foundation, Inc.
1.1       maekawa     4:
                      5: This file is part of the GNU MP Library.
                      6:
                      7: The GNU MP Library is free software; you can redistribute it and/or modify
1.1.1.2   maekawa     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
1.1       maekawa    10: option) any later version.
                     11:
                     12: The GNU MP Library is distributed in the hope that it will be useful, but
                     13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
1.1.1.2   maekawa    14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
1.1       maekawa    15: License for more details.
                     16:
1.1.1.2   maekawa    17: You should have received a copy of the GNU Lesser General Public License
1.1       maekawa    18: along with the GNU MP 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:
                     25: void
                     26: mpf_div_2exp (mpf_ptr r, mpf_srcptr u, unsigned long int exp)
                     27: {
                     28:   mp_srcptr up;
                     29:   mp_ptr rp = r->_mp_d;
                     30:   mp_size_t usize;
                     31:   mp_size_t abs_usize;
                     32:   mp_size_t prec = r->_mp_prec;
                     33:   mp_exp_t uexp = u->_mp_exp;
                     34:
                     35:   usize = u->_mp_size;
                     36:
                     37:   if (usize == 0)
                     38:     {
                     39:       r->_mp_size = 0;
                     40:       r->_mp_exp = 0;
                     41:       return;
                     42:     }
                     43:
                     44:   abs_usize = ABS (usize);
                     45:   up = u->_mp_d;
                     46:
1.1.1.3 ! ohara      47:   if (exp % GMP_NUMB_BITS == 0)
1.1       maekawa    48:     {
1.1.1.2   maekawa    49:       prec++;                  /* retain more precision here as we don't need
                     50:                                   to account for carry-out here */
                     51:       if (abs_usize > prec)
                     52:        {
                     53:          up += abs_usize - prec;
                     54:          abs_usize = prec;
                     55:        }
1.1       maekawa    56:       if (rp != up)
1.1.1.2   maekawa    57:        MPN_COPY_INCR (rp, up, abs_usize);
1.1.1.3 ! ohara      58:       r->_mp_exp = uexp - exp / GMP_NUMB_BITS;
1.1       maekawa    59:     }
                     60:   else
                     61:     {
                     62:       mp_limb_t cy_limb;
1.1.1.2   maekawa    63:       mp_size_t adj;
                     64:       if (abs_usize > prec)
                     65:        {
                     66:          up += abs_usize - prec;
                     67:          abs_usize = prec;
                     68:          /* Use mpn_rshift since mpn_lshift operates downwards, and we
                     69:             therefore would clobber part of U before using that part, in case
                     70:             R is the same variable as U.  */
1.1.1.3 ! ohara      71:          cy_limb = mpn_rshift (rp + 1, up, abs_usize, exp % GMP_NUMB_BITS);
1.1.1.2   maekawa    72:          rp[0] = cy_limb;
                     73:          adj = rp[abs_usize] != 0;
                     74:        }
                     75:       else
                     76:        {
1.1.1.3 ! ohara      77:          cy_limb = mpn_lshift (rp, up, abs_usize,
        !            78:                                GMP_NUMB_BITS - exp % GMP_NUMB_BITS);
1.1.1.2   maekawa    79:          rp[abs_usize] = cy_limb;
                     80:          adj = cy_limb != 0;
                     81:        }
1.1       maekawa    82:
1.1.1.2   maekawa    83:       abs_usize += adj;
1.1.1.3 ! ohara      84:       r->_mp_exp = uexp - exp / GMP_NUMB_BITS - 1 + adj;
1.1       maekawa    85:     }
                     86:   r->_mp_size = usize >= 0 ? abs_usize : -abs_usize;
                     87: }