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/* mpfr_round_raw_generic -- Generic rounding function
Copyright 1999, 2000, 2001, 2002, 2003, 2004 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. */
#ifndef flag
# error "ERROR: flag must be defined (0 / 1)"
#endif
#ifndef use_inexp
# error "ERROR: use_enexp must be defined (0 / 1)"
#endif
#ifndef mpfr_round_raw_generic
# error "ERROR: mpfr_round_raw_generic must be defined"
#endif
/*
* If flag = 0, puts in y the value of xp (with precision xprec and
* sign 1 if negative=0, -1 otherwise) rounded to precision yprec and
* direction rnd_mode. Supposes x is not zero nor NaN nor +/- Infinity
* (i.e. *xp != 0). In that case, the return value is a possible carry
* (0 or 1) that may happen during the rounding, in which case the result
* is a power of two.
*
* If inexp != NULL, put in *inexp the inexact flag of the rounding (0, 1, -1).
* In case of even rounding when rnd = GMP_RNDN, put MPFR_EVEN_INEX (2) or
* -MPFR_EVEN_INEX (-2) in *inexp.
*
* If flag = 1, just returns whether one should add 1 or not for rounding.
*
* Note: yprec may be < MPFR_PREC_MIN; in particular, it may be equal
* to 1. In this case, the even rounding is done away from 0, which is
* a natural generalization. Indeed, a number with 1-bit precision can
* be seen as a denormalized number with more precision.
*/
int
mpfr_round_raw_generic(mp_limb_t *yp, mp_limb_t *xp, mp_prec_t xprec,
int neg, mp_prec_t yprec, mp_rnd_t rnd_mode
#if use_inexp != 0
, int *inexp
#endif
)
{
mp_size_t xsize, nw;
mp_limb_t himask, lomask, sb;
int carry, rw;
#if use_inexp == 0
int *inexp;
#endif
if (use_inexp)
MPFR_ASSERTD(inexp != ((int*) 0));
MPFR_ASSERTD(neg == 0 || neg == 1);
if (flag && !use_inexp &&
(xprec <= yprec || MPFR_IS_LIKE_RNDZ (rnd_mode, neg)))
return 0;
xsize = (xprec-1)/BITS_PER_MP_LIMB + 1;
nw = yprec / BITS_PER_MP_LIMB;
rw = yprec & (BITS_PER_MP_LIMB - 1);
if (MPFR_UNLIKELY(xprec <= yprec))
{ /* No rounding is necessary. */
/* if yp=xp, maybe an overlap: MPN_COPY_DECR is ok when src <= dst */
if (MPFR_LIKELY(rw))
nw++;
MPFR_ASSERTD(nw >= 1);
MPFR_ASSERTD(nw >= xsize);
if (use_inexp)
*inexp = 0;
if (!flag)
{
MPN_COPY_DECR(yp + (nw - xsize), xp, xsize);
MPN_ZERO(yp, nw - xsize);
}
return 0;
}
if (use_inexp || !MPFR_IS_LIKE_RNDZ(rnd_mode, neg))
{
mp_size_t k = xsize - nw - 1;
if (MPFR_LIKELY(rw))
{
nw++;
lomask = MPFR_LIMB_MASK (BITS_PER_MP_LIMB - rw);
himask = ~lomask;
}
else
{
lomask = ~(mp_limb_t) 0;
himask = ~(mp_limb_t) 0;
}
MPFR_ASSERTD(k >= 0);
sb = xp[k] & lomask; /* First non-significant bits */
/* Rounding to nearest ? */
if (MPFR_LIKELY( rnd_mode == GMP_RNDN) )
{
/* Rounding to nearest */
mp_limb_t rbmask = MPFR_LIMB_ONE << (BITS_PER_MP_LIMB - 1 - rw);
if (sb & rbmask) /* rounding bit */
sb &= ~rbmask; /* it is 1, clear it */
else
{
/* Rounding bit is 0, behave like rounding to 0 */
goto rnd_RNDZ;
}
while (MPFR_UNLIKELY(sb == 0) && k > 0)
sb = xp[--k];
/* rounding to nearest, with rounding bit = 1 */
if (MPFR_UNLIKELY(sb == 0)) /* Even rounding. */
{
/* sb == 0 && rnd_mode == GMP_RNDN */
sb = xp[xsize - nw] & (himask ^ (himask << 1));
if (sb == 0)
{
if (use_inexp)
*inexp = 2*MPFR_EVEN_INEX*neg-MPFR_EVEN_INEX;
/* ((neg!=0)^(sb!=0)) ? MPFR_EVEN_INEX : -MPFR_EVEN_INEX;*/
/* Since neg = 0 or 1 and sb=0*/
if (flag)
return 0 /*sb != 0 && rnd_mode != GMP_RNDZ */;
MPN_COPY_INCR(yp, xp + xsize - nw, nw);
yp[0] &= himask;
return 0;
}
else
{
/* sb != 0 && rnd_mode == GMP_RNDN */
if (use_inexp)
*inexp = MPFR_EVEN_INEX-2*MPFR_EVEN_INEX*neg;
/*((neg!=0)^(sb!=0))? MPFR_EVEN_INEX : -MPFR_EVEN_INEX; */
/*Since neg= 0 or 1 and sb != 0 */
goto rnd_RNDN_add_one_ulp;
}
}
else /* sb != 0 && rnd_mode == GMP_RNDN*/
{
if (use_inexp)
/* *inexp = (neg == 0) ? 1 : -1; but since neg = 0 or 1 */
*inexp = 1-2*neg;
rnd_RNDN_add_one_ulp:
if (flag)
return 1; /*sb != 0 && rnd_mode != GMP_RNDZ;*/
carry = mpn_add_1 (yp, xp + xsize - nw, nw,
rw ?
MPFR_LIMB_ONE << (BITS_PER_MP_LIMB - rw)
: MPFR_LIMB_ONE);
yp[0] &= himask;
return carry;
}
}
/* Rounding to Zero ? */
else if (MPFR_IS_LIKE_RNDZ(rnd_mode, neg))
{
/* rnd_mode == GMP_RNDZ */
rnd_RNDZ:
while (MPFR_UNLIKELY(sb == 0) && k > 0)
sb = xp[--k];
if (use_inexp)
/* rnd_mode == GMP_RNDZ and neg = 0 or 1 */
/* (neg != 0) ^ (rnd_mode != GMP_RNDZ)) ? 1 : -1);*/
*inexp = MPFR_UNLIKELY(sb == 0) ? 0 : (2*neg-1);
if (flag)
return 0; /*sb != 0 && rnd_mode != GMP_RNDZ;*/
MPN_COPY_INCR(yp, xp + xsize - nw, nw);
yp[0] &= himask;
return 0;
}
else
{
/* rnd_mode = Away */
while (MPFR_UNLIKELY(sb == 0) && k > 0)
sb = xp[--k];
if (MPFR_UNLIKELY(sb == 0))
{
/* sb = 0 && rnd_mode != GMP_RNDZ */
if (use_inexp)
/* (neg != 0) ^ (rnd_mode != GMP_RNDZ)) ? 1 : -1);*/
*inexp = 0;
if (flag)
return 0;
MPN_COPY_INCR(yp, xp + xsize - nw, nw);
yp[0] &= himask;
return 0;
}
else
{
/* sb != 0 && rnd_mode != GMP_RNDZ */
if (use_inexp)
/* (neg != 0) ^ (rnd_mode != GMP_RNDZ)) ? 1 : -1);*/
*inexp = 1-2*neg;
if (flag)
return 1;
carry = mpn_add_1(yp, xp + xsize - nw, nw,
rw ? MPFR_LIMB_ONE << (BITS_PER_MP_LIMB - rw)
: 1);
yp[0] &= himask;
return carry;
}
}
}
else
{
/* Roundind mode = Zero / No inexact flag */
if (flag)
return 0 /*sb != 0 && rnd_mode != GMP_RNDZ*/;
if (MPFR_LIKELY(rw))
{
nw++;
himask = ~MPFR_LIMB_MASK (BITS_PER_MP_LIMB - rw);
}
else
himask = ~(mp_limb_t) 0;
MPN_COPY_INCR(yp, xp + xsize - nw, nw);
yp[0] &= himask;
return 0;
}
}
#undef flag
#undef use_inexp
#undef mpfr_round_raw_generic
|
