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/* mpfr_get_z_exp -- get a multiple-precision integer and an exponent
from a floating-point number
Copyright 2000, 2001, 2002, 2003, 2004, 2005, 2006 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., 51 Franklin St, Fifth Floor, Boston,
MA 02110-1301, USA. */
#include "mpfr-impl.h"
/* puts the mantissa of f into z, and returns 'exp' such that f = z * 2^exp
*
* 0 doesn't have an exponent, therefore the returned exponent in this case
* isn't really important. We choose to return __gmpfr_emin because
* 1) it is in the exponent range [__gmpfr_emin,__gmpfr_emax],
* 2) the smaller a number is (in absolute value), the smaller its
* exponent is. In other words, the f -> exp function is monotonous
* on nonnegative numbers.
* Note that this is different from the C function frexp().
*/
mp_exp_t
mpfr_get_z_exp (mpz_ptr z, mpfr_srcptr f)
{
mp_size_t fn;
int sh;
MPFR_ASSERTD (MPFR_IS_FP (f));
if (MPFR_UNLIKELY (MPFR_IS_ZERO (f)))
{
mpz_set_ui (z, 0);
return __gmpfr_emin;
}
fn = MPFR_LIMB_SIZE(f);
/* check whether allocated space for z is enough */
if (MPFR_UNLIKELY (ALLOC (z) < fn))
MPZ_REALLOC (z, fn);
MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC (f));
if (MPFR_LIKELY (sh))
mpn_rshift (PTR (z), MPFR_MANT (f), fn, sh);
else
MPN_COPY (PTR (z), MPFR_MANT (f), fn);
SIZ(z) = MPFR_IS_NEG (f) ? -fn : fn;
/* Test if the result is representable. Later, we could choose
to return MPFR_EXP_MIN if it isn't, or perhaps MPFR_EXP_MAX
to signal an error. The mantissa would still be meaningful. */
MPFR_ASSERTD ((mp_exp_unsigned_t) MPFR_GET_EXP (f) - MPFR_EXP_MIN
>= (mp_exp_unsigned_t) MPFR_PREC(f));
return MPFR_GET_EXP (f) - MPFR_PREC (f);
}
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