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/* mpfr_cmp_si_2exp -- compare a floating-point number with a signed
machine integer multiplied by a power of 2
Copyright 1999, 2001, 2002 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 "gmp-impl.h"
#include "longlong.h"
#include "mpfr.h"
#include "mpfr-impl.h"
/* returns a positive value if b > i*2^f,
a negative value if b < i*2^f,
zero if b = i*2^f.
b must not be NaN.
*/
int
mpfr_cmp_si_2exp (mpfr_srcptr b, long int i, mp_exp_t f)
{
int si;
MPFR_ASSERTN(!MPFR_IS_NAN(b));
si = i < 0 ? -1 : 1; /* sign of i */
if (MPFR_IS_INF(b) || (MPFR_NOTZERO(b) && MPFR_SIGN(b) != si))
return MPFR_SIGN(b);
/* both signs differ or b = 0 */
else if (MPFR_IS_ZERO(b))
return i != 0 ? -si : 0;
else if (i == 0)
return MPFR_SIGN(b);
else /* b and i are of same sign si */
{
mp_exp_t e;
unsigned long ai;
int k;
mp_size_t bn;
mp_limb_t c, *bp;
ai = SAFE_ABS(unsigned long, i);
/* ai must be representable in a mp_limb_t */
MPFR_ASSERTN(ai == (mp_limb_t) ai);
e = MPFR_EXP(b); /* 2^(e-1) <= b < 2^e */
if (e <= f)
return -si;
if (f < MPFR_EMAX_MAX - BITS_PER_MP_LIMB &&
e > f + BITS_PER_MP_LIMB)
return si;
/* now f < e <= f + BITS_PER_MP_LIMB */
c = (mp_limb_t) ai;
count_leading_zeros(k, c);
if ((int) (e - f) > BITS_PER_MP_LIMB - k)
return si;
if ((int) (e - f) < BITS_PER_MP_LIMB - k)
return -si;
/* now b and i*2^f have the same exponent */
c <<= k;
bn = (MPFR_PREC(b) - 1) / BITS_PER_MP_LIMB;
bp = MPFR_MANT(b);
if (bp[bn] > c)
return si;
if (bp[bn] < c)
return -si;
/* most significant limbs agree, check remaining limbs from b */
while (bn > 0)
if (bp[--bn])
return si;
return 0;
}
}
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