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/* mpfr_add_one_ulp, mpfr_sub_one_ulp -- add/subtract one unit in last place
Copyright (C) 1999, 2001 Free Software Foundation, Inc.
This file is part of the MPFR Library.
The MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.
The MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the MPFR Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "mpfr.h"
#include "mpfr-impl.h"
#include "gmp-impl.h"
/* sets x to x+sign(x)*2^(MPFR_EXP(x)-MPFR_PREC(x)) */
void
mpfr_add_one_ulp (mpfr_ptr x)
{
int xn, sh;
mp_limb_t *xp;
if (MPFR_IS_INF(x))
return;
xn = 1 + (MPFR_PREC(x) - 1) / BITS_PER_MP_LIMB;
sh = xn * BITS_PER_MP_LIMB - MPFR_PREC(x);
xp = MPFR_MANT(x);
if (mpn_add_1 (xp, xp, xn, MP_LIMB_T_ONE << sh)) /* got 1.0000... */
{
MPFR_EXP(x)++;
xp[xn-1] = MP_LIMB_T_HIGHBIT;
}
return;
}
/* sets x to x-sign(x)*ulp(x) */
void
mpfr_sub_one_ulp(mpfr_ptr x)
{
int xn, sh;
mp_limb_t *xp;
if (MPFR_IS_INF(x))
return;
xn = 1 + (MPFR_PREC(x) - 1) / BITS_PER_MP_LIMB;
sh = xn * BITS_PER_MP_LIMB - MPFR_PREC(x);
xp = MPFR_MANT(x);
mpn_sub_1 (xp, xp, xn, MP_LIMB_T_ONE << sh);
if (xp[xn-1] >> (BITS_PER_MP_LIMB - 1) == 0) {
/* was an exact power of two: not normalized any more */
MPFR_EXP(x)--;
mpn_lshift (xp, xp, xn, 1);
*xp |= MP_LIMB_T_ONE << sh;
}
return;
}
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