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Annotation of OpenXM_contrib/gmp/mpfr/sub_one_ulp.c, Revision 1.1.1.1

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: }