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Annotation of OpenXM_contrib/gmp/mpf/div_2exp.c, Revision 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: }