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Annotation of OpenXM_contrib/gmp/mpf/div_2exp.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpf_div_2exp -- Divide a float by 2^n.
                      2:
                      3: Copyright (C) 1993, 1994, 1996 Free Software Foundation, Inc.
                      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
                      8: it under the terms of the GNU Library General Public License as published by
                      9: the Free Software Foundation; either version 2 of the License, or (at your
                     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
                     14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
                     15: License for more details.
                     16:
                     17: You should have received a copy of the GNU Library General Public License
                     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 (abs_usize > prec)
                     55:     {
                     56:       up += abs_usize - prec;
                     57:       abs_usize = prec;
                     58:     }
                     59:
                     60:   if (exp % BITS_PER_MP_LIMB == 0)
                     61:     {
                     62:       if (rp != up)
                     63:        MPN_COPY (rp, up, abs_usize);
                     64:       r->_mp_exp = uexp - exp / BITS_PER_MP_LIMB;
                     65:     }
                     66:   else
                     67:     {
                     68:       /* Use mpn_lshift since mpn_rshift operates upwards, and we therefore
                     69:         would clobber part of U before using that part, when R == U.  */
                     70:       mp_limb_t cy_limb;
                     71:       cy_limb = mpn_lshift (rp, up, abs_usize, -exp % BITS_PER_MP_LIMB);
                     72:       rp[abs_usize] = cy_limb;
                     73:       cy_limb = cy_limb != 0;
                     74:
                     75:       abs_usize += cy_limb;
                     76:       r->_mp_exp = uexp - exp / BITS_PER_MP_LIMB - 1 + cy_limb;
                     77:     }
                     78:   r->_mp_size = usize >= 0 ? abs_usize : -abs_usize;
                     79: }