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Annotation of OpenXM_contrib/gmp/mpfr/sub_one_ulp.c, Revision 1.1

1.1     ! ohara       1: /* mpfr_sub_one_ulp -- subtract one unit in last place
        !             2:
        !             3: Copyright 1999, 2001 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: /* sets x to x-sign(x)*ulp(x) */
        !            28: int
        !            29: mpfr_sub_one_ulp(mpfr_ptr x, mp_rnd_t rnd_mode)
        !            30: {
        !            31:   mp_size_t xn;
        !            32:   int sh;
        !            33:   mp_limb_t *xp;
        !            34:
        !            35:   if (MPFR_IS_NAN(x))
        !            36:     MPFR_RET_NAN;
        !            37:
        !            38:   if (MPFR_IS_INF(x) || MPFR_IS_ZERO(x))
        !            39:     return 0;
        !            40:
        !            41:   MPFR_ASSERTN(MPFR_PREC_MIN > 1);
        !            42:
        !            43:   xn = 1 + (MPFR_PREC(x) - 1) / BITS_PER_MP_LIMB;
        !            44:   sh = xn * BITS_PER_MP_LIMB - MPFR_PREC(x);
        !            45:   xp = MPFR_MANT(x);
        !            46:   mpn_sub_1 (xp, xp, xn, MP_LIMB_T_ONE << sh);
        !            47:   if (xp[xn-1] >> (BITS_PER_MP_LIMB - 1) == 0)
        !            48:     { /* was an exact power of two: not normalized any more */
        !            49:       mp_exp_t exp = MPFR_EXP(x);
        !            50:       if (exp == __mpfr_emin)
        !            51:         return mpfr_set_underflow(x, rnd_mode, MPFR_SIGN(x));
        !            52:       else
        !            53:         {
        !            54:           int i;
        !            55:           MPFR_EXP(x)--;
        !            56:           xp[0] = (sh + 1 == BITS_PER_MP_LIMB) ? 0 : MP_LIMB_T_MAX << (sh + 1);
        !            57:           for (i = 1; i < xn; i++)
        !            58:             xp[i] = MP_LIMB_T_MAX;
        !            59:         }
        !            60:     }
        !            61:   return 0;
        !            62: }