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

1.1       maekawa     1: /* mpfr_add_one_ulp, mpfr_sub_one_ulp -- add/subtract one unit in last place
                      2:
                      3: Copyright (C) 1999 PolKA project, Inria Lorraine and Loria
                      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 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 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 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 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:
                     26: /* sets x to x+sign(x)*2^(EXP(x)-PREC(x)) */
                     27: int
                     28: #if __STDC__
                     29: mpfr_add_one_ulp(mpfr_ptr x)
                     30: #else
                     31: mpfr_add_one_ulp(x)
                     32:      mpfr_ptr x;
                     33: #endif
                     34: {
                     35:   int xn, sh; mp_limb_t *xp;
                     36:
                     37:   xn = 1 + (PREC(x)-1)/BITS_PER_MP_LIMB;
                     38:   sh = xn*BITS_PER_MP_LIMB - PREC(x);
                     39:   xp = MANT(x);
                     40:   if (mpn_add_1(xp, xp, xn, (mp_limb_t)1<<sh)) {
                     41:     EXP(x)++;
                     42:     mpn_rshift(xp, xp, xn, 1);
                     43:     xp[xn-1] += (mp_limb_t)1<<(BITS_PER_MP_LIMB-1);
                     44:   }
                     45:   return 0;
                     46: }
                     47:
                     48: /* sets x to x-sign(x)*ulp(x) */
                     49: int mpfr_sub_one_ulp(mpfr_ptr x)
                     50: {
                     51:   int xn, sh; mp_limb_t *xp;
                     52:
                     53:   xn = 1 + (PREC(x)-1)/BITS_PER_MP_LIMB;
                     54:   sh = xn*BITS_PER_MP_LIMB-PREC(x);
                     55:   xp = MANT(x);
                     56:   mpn_sub_1(xp, xp, xn, (mp_limb_t)1<<sh);
                     57:   if (xp[xn-1] >> (BITS_PER_MP_LIMB-1) == 0) {
                     58:     /* was an exact power of two: not normalized any more */
                     59:     EXP(x)--;
                     60:     mpn_lshift(xp, xp, xn, 1);
                     61:     *xp |= ((mp_limb_t)1 << sh);
                     62:   }
                     63:   return 0;
                     64: }