get_si.c revision 1.1.1.3
1/* mpfr_get_si -- convert a floating-point number to a signed long. 2 3Copyright 2003-2018 Free Software Foundation, Inc. 4Contributed by the AriC and Caramba projects, INRIA. 5 6This file is part of the GNU MPFR Library. 7 8The GNU MPFR Library is free software; you can redistribute it and/or modify 9it under the terms of the GNU Lesser General Public License as published by 10the Free Software Foundation; either version 3 of the License, or (at your 11option) any later version. 12 13The GNU MPFR Library is distributed in the hope that it will be useful, but 14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16License for more details. 17 18You should have received a copy of the GNU Lesser General Public License 19along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 20http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 2151 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 22 23#include "mpfr-impl.h" 24 25long 26mpfr_get_si (mpfr_srcptr f, mpfr_rnd_t rnd) 27{ 28 mpfr_prec_t prec; 29 long s; 30 mpfr_t x; 31 MPFR_SAVE_EXPO_DECL (expo); 32 33 if (MPFR_UNLIKELY (!mpfr_fits_slong_p (f, rnd))) 34 { 35 MPFR_SET_ERANGEFLAG (); 36 return MPFR_IS_NAN (f) ? 0 : 37 MPFR_IS_NEG (f) ? LONG_MIN : LONG_MAX; 38 } 39 40 if (MPFR_IS_ZERO (f)) 41 return (long) 0; 42 43 /* Determine the precision of long. |LONG_MIN| may have one more bit 44 as an integer, but in this case, this is a power of 2, thus fits 45 in a precision-prec floating-point number. */ 46 for (s = LONG_MAX, prec = 0; s != 0; s /= 2, prec++) 47 { } 48 49 MPFR_SAVE_EXPO_MARK (expo); 50 51 /* first round to prec bits */ 52 mpfr_init2 (x, prec); 53 mpfr_rint (x, f, rnd); 54 55 /* The flags from mpfr_rint are the wanted ones. In particular, 56 it sets the inexact flag when necessary. */ 57 MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags); 58 59 /* warning: if x=0, taking its exponent is illegal */ 60 if (MPFR_UNLIKELY (MPFR_IS_ZERO(x))) 61 s = 0; 62 else 63 { 64 mp_limb_t a; 65 mp_size_t n; 66 mpfr_exp_t exp; 67 68 /* now the result is in the most significant limb of x */ 69 exp = MPFR_GET_EXP (x); /* since |x| >= 1, exp >= 1 */ 70 n = MPFR_LIMB_SIZE(x); 71 a = MPFR_MANT(x)[n - 1] >> (GMP_NUMB_BITS - exp); 72 s = MPFR_IS_POS (f) ? a : a <= LONG_MAX ? - (long) a : LONG_MIN; 73 } 74 75 mpfr_clear (x); 76 77 MPFR_SAVE_EXPO_FREE (expo); 78 79 return s; 80} 81