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Annotation of OpenXM_contrib/gmp/mpf/div_2exp.c, Revision 1.1.1.2

1.1       maekawa     1: /* mpf_div_2exp -- Divide a float by 2^n.
                      2:
1.1.1.2 ! maekawa     3: Copyright (C) 1993, 1994, 1996, 2000 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: #if __STDC__
                     27: mpf_div_2exp (mpf_ptr r, mpf_srcptr u, unsigned long int exp)
                     28: #else
                     29: mpf_div_2exp (r, u, exp)
                     30:      mpf_ptr r;
                     31:      mpf_srcptr u;
                     32:      unsigned long int exp;
                     33: #endif
                     34: {
                     35:   mp_srcptr up;
                     36:   mp_ptr rp = r->_mp_d;
                     37:   mp_size_t usize;
                     38:   mp_size_t abs_usize;
                     39:   mp_size_t prec = r->_mp_prec;
                     40:   mp_exp_t uexp = u->_mp_exp;
                     41:
                     42:   usize = u->_mp_size;
                     43:
                     44:   if (usize == 0)
                     45:     {
                     46:       r->_mp_size = 0;
                     47:       r->_mp_exp = 0;
                     48:       return;
                     49:     }
                     50:
                     51:   abs_usize = ABS (usize);
                     52:   up = u->_mp_d;
                     53:
                     54:   if (exp % BITS_PER_MP_LIMB == 0)
                     55:     {
1.1.1.2 ! maekawa    56:       prec++;                  /* retain more precision here as we don't need
        !            57:                                   to account for carry-out here */
        !            58:       if (abs_usize > prec)
        !            59:        {
        !            60:          up += abs_usize - prec;
        !            61:          abs_usize = prec;
        !            62:        }
1.1       maekawa    63:       if (rp != up)
1.1.1.2 ! maekawa    64:        MPN_COPY_INCR (rp, up, abs_usize);
1.1       maekawa    65:       r->_mp_exp = uexp - exp / BITS_PER_MP_LIMB;
                     66:     }
                     67:   else
                     68:     {
                     69:       mp_limb_t cy_limb;
1.1.1.2 ! maekawa    70:       mp_size_t adj;
        !            71:       if (abs_usize > prec)
        !            72:        {
        !            73:          up += abs_usize - prec;
        !            74:          abs_usize = prec;
        !            75:          /* Use mpn_rshift since mpn_lshift operates downwards, and we
        !            76:             therefore would clobber part of U before using that part, in case
        !            77:             R is the same variable as U.  */
        !            78:          cy_limb = mpn_rshift (rp + 1, up, abs_usize, exp % BITS_PER_MP_LIMB);
        !            79:          rp[0] = cy_limb;
        !            80:          adj = rp[abs_usize] != 0;
        !            81:        }
        !            82:       else
        !            83:        {
        !            84:          cy_limb = mpn_lshift (rp, up, abs_usize, (-exp) % BITS_PER_MP_LIMB);
        !            85:          rp[abs_usize] = cy_limb;
        !            86:          adj = cy_limb != 0;
        !            87:        }
1.1       maekawa    88:
1.1.1.2 ! maekawa    89:       abs_usize += adj;
        !            90:       r->_mp_exp = uexp - exp / BITS_PER_MP_LIMB - 1 + adj;
1.1       maekawa    91:     }
                     92:   r->_mp_size = usize >= 0 ? abs_usize : -abs_usize;
                     93: }