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/* mpfr_frac -- Fractional part of a floating-point number.
Copyright 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. */
#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"
/* Optimization note: it is not a good idea to call mpfr_integer_p,
as some cases will take longer (the number may be parsed twice). */
int
mpfr_frac (mpfr_ptr r, mpfr_srcptr u, mp_rnd_t rnd_mode)
{
mp_exp_t re, ue;
mp_prec_t uq, fq;
mp_size_t un, tn, t0;
mp_limb_t *up, *tp, k;
int sh;
mpfr_t tmp;
mpfr_ptr t;
/* Special cases */
if (MPFR_UNLIKELY(MPFR_IS_NAN(u)))
{
MPFR_SET_NAN(r);
MPFR_RET_NAN;
}
else if (MPFR_UNLIKELY(MPFR_IS_INF(u) || mpfr_integer_p (u)))
{
MPFR_CLEAR_FLAGS(r);
MPFR_SET_SAME_SIGN(r, u);
MPFR_SET_ZERO(r);
MPFR_RET(0); /* zero is exact */
}
ue = MPFR_GET_EXP (u);
if (ue <= 0) /* |u| < 1 */
return mpfr_set (r, u, rnd_mode);
uq = MPFR_PREC(u);
un = (uq - 1) / BITS_PER_MP_LIMB; /* index of most significant limb */
un -= (mp_size_t) (ue / BITS_PER_MP_LIMB);
/* now the index of the MSL containing bits of the fractional part */
up = MPFR_MANT(u);
sh = ue % BITS_PER_MP_LIMB;
k = up[un] << sh;
/* the first bit of the fractional part is the MSB of k */
if (k != 0)
{
int cnt;
count_leading_zeros(cnt, k);
/* first bit 1 of the fractional part -> MSB of the number */
re = -cnt;
sh += cnt;
MPFR_ASSERTN (sh < BITS_PER_MP_LIMB);
k <<= cnt;
}
else
{
re = sh - BITS_PER_MP_LIMB;
/* searching for the first bit 1 (exists since u isn't an integer) */
while (up[--un] == 0)
re -= BITS_PER_MP_LIMB;
MPFR_ASSERTN(un >= 0);
k = up[un];
count_leading_zeros(sh, k);
re -= sh;
k <<= sh;
}
/* The exponent of r will be re */
/* un: index of the limb of u that contains the first bit 1 of the FP */
ue -= re; /* number of bits of u to discard */
fq = uq - ue; /* number of bits of the fractional part of u */
/* Temporary fix */
t = /* fq > MPFR_PREC(r) */
(mp_size_t) (MPFR_PREC(r) - 1) / BITS_PER_MP_LIMB < un ?
(mpfr_init2 (tmp, (un + 1) * BITS_PER_MP_LIMB), tmp) : r;
/* t has enough precision to contain the fractional part of u */
/* If we use a temporary variable, we take the non-significant bits
of u into account, because of the mpn_lshift below. */
MPFR_CLEAR_FLAGS(t);
MPFR_SET_SAME_SIGN(t, u);
MPFR_SET_EXP (t, re);
/* Put the fractional part of u into t */
tn = (MPFR_PREC(t) - 1) / BITS_PER_MP_LIMB;
MPFR_ASSERTN(tn >= un);
t0 = tn - un;
tp = MPFR_MANT(t);
if (sh == 0)
MPN_COPY_DECR(tp + t0, up, un + 1);
else /* warning: un may be 0 here */
tp[tn] = k | ((un) ? mpn_lshift (tp + t0, up, un, sh) : (mp_limb_t) 0);
if (t0 > 0)
MPN_ZERO(tp, t0);
if (t != r)
{ /* t is tmp */
int inex;
inex = mpfr_set (r, t, rnd_mode);
mpfr_clear (t);
return inex;
}
else
MPFR_RET(0);
}
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