/* mpfr_get_z_exp -- get a multiple-precision integer and an exponent from a floating-point number Copyright 2000, 2001, 2002, 2003, 2004, 2005 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 "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); }