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/* mpfr_get_z_2exp -- get a multiple-precision integer and an exponent
from a floating-point number
Copyright 2000-2021 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU 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 3 of the License, or (at your
option) any later version.
The GNU 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 GNU MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#include "mpfr-impl.h"
/* puts the significand 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. --> This is WRONG since the returned
* exponent is not necessarily in the exponent range!
* Note that this is different from the C function frexp().
*
* For NaN and infinities, we choose to set z = 0 (neutral value).
* The exponent doesn't really matter, so let's keep __gmpfr_emin
* for consistency. The erange flag is set.
*/
/* MPFR_LARGE_EXP can be defined when mpfr_exp_t is guaranteed to have
at least 64 bits (in a portable way). */
#if GMP_NUMB_BITS >= 64
/* Now, we know that the constant below is supported by the compiler. */
# if _MPFR_EXP_FORMAT >= 3 && LONG_MAX >= 9223372036854775807
# define MPFR_LARGE_EXP 1
# endif
#endif
mpfr_exp_t
mpfr_get_z_2exp (mpz_ptr z, mpfr_srcptr f)
{
mp_size_t fn;
int sh;
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
{
if (MPFR_UNLIKELY (MPFR_NOTZERO (f)))
MPFR_SET_ERANGEFLAG ();
mpz_set_ui (z, 0);
return __gmpfr_emin;
}
fn = MPFR_LIMB_SIZE(f);
/* FIXME: temporary assert for security. Too large values should
probably be handled like infinities. */
MPFR_ASSERTN (fn <= INT_MAX); /* due to SIZ(z) being an int */
/* check whether allocated space for z is enough */
mpz_realloc2 (z, (mp_bitcnt_t) fn * GMP_NUMB_BITS);
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;
#ifndef MPFR_LARGE_EXP
/* If mpfr_exp_t has 64 bits, then MPFR_GET_EXP(f) >= MPFR_EMIN_MIN = 1-2^62
and MPFR_EXP_MIN <= 1-2^63, thus the following implies PREC(f) > 2^62,
which is impossible due to memory constraints. */
if (MPFR_UNLIKELY ((mpfr_uexp_t) MPFR_GET_EXP (f) - MPFR_EXP_MIN
< (mpfr_uexp_t) MPFR_PREC (f)))
{
/* The exponent isn't representable in an mpfr_exp_t. */
MPFR_SET_ERANGEFLAG ();
return MPFR_EXP_MIN;
}
#endif
return MPFR_GET_EXP (f) - MPFR_PREC (f);
}
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