1 /* mpfr_div_2ui -- divide a floating-point number by a power of two 2 3 Copyright 1999, 2001-2023 Free Software Foundation, Inc. 4 Contributed by the AriC and Caramba projects, INRIA. 5 6 This file is part of the GNU MPFR Library. 7 8 The GNU MPFR Library is free software; you can redistribute it and/or modify 9 it under the terms of the GNU Lesser General Public License as published by 10 the Free Software Foundation; either version 3 of the License, or (at your 11 option) any later version. 12 13 The GNU MPFR Library is distributed in the hope that it will be useful, but 14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16 License for more details. 17 18 You should have received a copy of the GNU Lesser General Public License 19 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 20 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 22 23 #include "mpfr-impl.h" 24 25 int 26 mpfr_div_2ui (mpfr_ptr y, mpfr_srcptr x, unsigned long n, mpfr_rnd_t rnd_mode) 27 { 28 int inexact; 29 30 MPFR_LOG_FUNC ( 31 ("x[%Pu]=%.*Rg n=%lu rnd=%d", mpfr_get_prec(x), mpfr_log_prec, x, n, 32 rnd_mode), 33 ("y[%Pu]=%.*Rg inexact=%d", mpfr_get_prec(y), mpfr_log_prec, y, inexact)); 34 35 if (MPFR_UNLIKELY (n == 0 || MPFR_IS_SINGULAR (x))) 36 return mpfr_set (y, x, rnd_mode); 37 else 38 { 39 mpfr_exp_t exp = MPFR_GET_EXP (x); 40 mpfr_uexp_t diffexp; 41 42 MPFR_SETRAW (inexact, y, x, exp, rnd_mode); 43 /* Warning! exp may have increased by 1 due to rounding. Thus the 44 difference below may overflow in a mpfr_exp_t; but mpfr_uexp_t 45 is OK to hold the value, with the difference done in unsigned 46 integer arithmetic in this type. */ 47 diffexp = (mpfr_uexp_t) exp - (mpfr_uexp_t) (__gmpfr_emin - 1); 48 if (MPFR_UNLIKELY (n >= diffexp)) /* exp - n <= emin - 1 */ 49 { 50 if (rnd_mode == MPFR_RNDN && 51 (n > diffexp || 52 ((MPFR_IS_NEG (y) ? inexact <= 0 : inexact >= 0) && 53 mpfr_powerof2_raw (y)))) 54 rnd_mode = MPFR_RNDZ; 55 return mpfr_underflow (y, rnd_mode, MPFR_SIGN (y)); 56 } 57 /* Now, n < diffexp, i.e. n <= exp - emin, which a difference of 58 * two valid exponents + 0 or 1, thus fits in a mpfr_exp_t (from 59 * the constraints on valid exponents). Moreover, there cannot be 60 * an overflow (if exp had been increased by 1 due to rounding) 61 * since the case n = 0 has been filtered out. 62 */ 63 MPFR_ASSERTD (n <= MPFR_EXP_MAX); 64 MPFR_ASSERTD (n >= 1); 65 MPFR_SET_EXP (y, exp - (mpfr_exp_t) n); 66 } 67 68 MPFR_RET (inexact); 69 } 70