1 /* mpfr_get_z_2exp -- get a multiple-precision integer and an exponent 2 from a floating-point number 3 4 Copyright 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc. 5 Contributed by the AriC and Caramel projects, INRIA. 6 7 This file is part of the GNU MPFR Library. 8 9 The GNU MPFR Library is free software; you can redistribute it and/or modify 10 it under the terms of the GNU Lesser General Public License as published by 11 the Free Software Foundation; either version 3 of the License, or (at your 12 option) any later version. 13 14 The GNU MPFR Library is distributed in the hope that it will be useful, but 15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 17 License for more details. 18 19 You should have received a copy of the GNU Lesser General Public License 20 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 21 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 22 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 23 24 #include "mpfr-impl.h" 25 26 /* puts the significand of f into z, and returns 'exp' such that f = z * 2^exp 27 * 28 * 0 doesn't have an exponent, therefore the returned exponent in this case 29 * isn't really important. We choose to return __gmpfr_emin because 30 * 1) it is in the exponent range [__gmpfr_emin,__gmpfr_emax], 31 * 2) the smaller a number is (in absolute value), the smaller its 32 * exponent is. In other words, the f -> exp function is monotonous 33 * on nonnegative numbers. --> This is WRONG since the returned 34 * exponent is not necessarily in the exponent range! 35 * Note that this is different from the C function frexp(). 36 * 37 * For NaN and infinities, we choose to set z = 0 (neutral value). 38 * The exponent doesn't really matter, so let's keep __gmpfr_emin 39 * for consistency. The erange flag is set. 40 */ 41 42 mpfr_exp_t 43 mpfr_get_z_2exp (mpz_ptr z, mpfr_srcptr f) 44 { 45 mp_size_t fn; 46 int sh; 47 48 if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f))) 49 { 50 if (MPFR_UNLIKELY (MPFR_NOTZERO (f))) 51 MPFR_SET_ERANGE (); 52 mpz_set_ui (z, 0); 53 return __gmpfr_emin; 54 } 55 56 fn = MPFR_LIMB_SIZE(f); 57 58 /* check whether allocated space for z is enough */ 59 if (MPFR_UNLIKELY (ALLOC (z) < fn)) 60 MPZ_REALLOC (z, fn); 61 62 MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC (f)); 63 if (MPFR_LIKELY (sh)) 64 mpn_rshift (PTR (z), MPFR_MANT (f), fn, sh); 65 else 66 MPN_COPY (PTR (z), MPFR_MANT (f), fn); 67 68 SIZ(z) = MPFR_IS_NEG (f) ? -fn : fn; 69 70 if (MPFR_UNLIKELY ((mpfr_uexp_t) MPFR_GET_EXP (f) - MPFR_EXP_MIN 71 < (mpfr_uexp_t) MPFR_PREC (f))) 72 { 73 /* The exponent isn't representable in an mpfr_exp_t. */ 74 MPFR_SET_ERANGE (); 75 return MPFR_EXP_MIN; 76 } 77 78 return MPFR_GET_EXP (f) - MPFR_PREC (f); 79 } 80