| /* Round according to the current rounding mode. |
| Copyright (C) 2007, 2010-2020 Free Software Foundation, Inc. |
| |
| This program is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2, or (at your option) |
| any later version. |
| |
| This program 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 General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License along |
| with this program; if not, see <https://www.gnu.org/licenses/>. */ |
| |
| #if ! defined USE_LONG_DOUBLE |
| # include <config.h> |
| #endif |
| |
| /* Specification. */ |
| #include <math.h> |
| |
| #include <float.h> |
| #include <stdlib.h> |
| |
| #undef MIN |
| |
| #ifdef USE_LONG_DOUBLE |
| # define RINT rintl |
| # define DOUBLE long double |
| # define MANT_DIG LDBL_MANT_DIG |
| # define MIN LDBL_MIN |
| # define L_(literal) literal##L |
| #elif ! defined USE_FLOAT |
| # define RINT rint |
| # define DOUBLE double |
| # define MANT_DIG DBL_MANT_DIG |
| # define MIN DBL_MIN |
| # define L_(literal) literal |
| #else /* defined USE_FLOAT */ |
| # define RINT rintf |
| # define DOUBLE float |
| # define MANT_DIG FLT_MANT_DIG |
| # define MIN FLT_MIN |
| # define L_(literal) literal##f |
| #endif |
| |
| /* -0.0. See minus-zero.h. */ |
| #if defined __hpux || defined __sgi || defined __ICC |
| # define MINUS_ZERO (-MIN * MIN) |
| #else |
| # define MINUS_ZERO L_(-0.0) |
| #endif |
| |
| /* MSVC with option -fp:strict refuses to compile constant initializers that |
| contain floating-point operations. Pacify this compiler. */ |
| #ifdef _MSC_VER |
| # pragma fenv_access (off) |
| #endif |
| |
| DOUBLE |
| RINT (DOUBLE x) |
| { |
| /* 2^(MANT_DIG-1). */ |
| static const DOUBLE TWO_MANT_DIG = |
| /* Assume MANT_DIG <= 5 * 31. |
| Use the identity |
| n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */ |
| (DOUBLE) (1U << ((MANT_DIG - 1) / 5)) |
| * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5)) |
| * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5)) |
| * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5)) |
| * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5)); |
| |
| /* The use of 'volatile' guarantees that excess precision bits are dropped at |
| each addition step and before the following comparison at the caller's |
| site. It is necessary on x86 systems where double-floats are not IEEE |
| compliant by default, to avoid that the results become platform and |
| compiler option dependent. 'volatile' is a portable alternative to gcc's |
| -ffloat-store option. */ |
| volatile DOUBLE z = x; |
| |
| /* Consider the current rounding mode, cf. |
| <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/float.h.html>. |
| This implementation supports only rounds-to-nearest. */ |
| if (FLT_ROUNDS != 1) |
| abort (); |
| |
| if (z > L_(0.0)) |
| { |
| /* Avoid rounding error for x = 0.5 - 2^(-MANT_DIG-1). */ |
| if (z < L_(0.5)) |
| z = L_(0.0); |
| /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1. */ |
| else if (z < TWO_MANT_DIG) |
| { |
| /* Round to the next integer. */ |
| z += TWO_MANT_DIG; |
| z -= TWO_MANT_DIG; |
| } |
| } |
| else if (z < L_(0.0)) |
| { |
| /* Avoid rounding error for x = -(0.5 - 2^(-MANT_DIG-1)). */ |
| if (z > - L_(0.5)) |
| z = MINUS_ZERO; |
| /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1. */ |
| else if (z > -TWO_MANT_DIG) |
| { |
| /* Round to the next integer. */ |
| z -= TWO_MANT_DIG; |
| z += TWO_MANT_DIG; |
| } |
| } |
| return z; |
| } |