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e2239af353
Improve the commentary to aid future developers who will stumble upon this novel, yet not always perfect, mechanism to support alternative formats for long double. Likewise, rename __LONG_DOUBLE_USES_FLOAT128 to __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI now that development work has settled down. The command used was git grep -l __LONG_DOUBLE_USES_FLOAT128 ':!./ChangeLog*' | \ xargs sed -i 's/__LONG_DOUBLE_USES_FLOAT128/__LDOUBLE_REDIRECTS_TO_FLOAT128_ABI/g' Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
198 lines
5.2 KiB
C
198 lines
5.2 KiB
C
/* Copyright (C) 1992-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef _IEEE754_H
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#define _IEEE754_H 1
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#include <features.h>
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#include <bits/endian.h>
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#include <bits/floatn.h>
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__BEGIN_DECLS
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union ieee754_float
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{
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float f;
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/* This is the IEEE 754 single-precision format. */
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struct
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{
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#if __BYTE_ORDER == __BIG_ENDIAN
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unsigned int negative:1;
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unsigned int exponent:8;
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unsigned int mantissa:23;
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#endif /* Big endian. */
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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unsigned int mantissa:23;
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unsigned int exponent:8;
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unsigned int negative:1;
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#endif /* Little endian. */
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} ieee;
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/* This format makes it easier to see if a NaN is a signalling NaN. */
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struct
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{
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#if __BYTE_ORDER == __BIG_ENDIAN
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unsigned int negative:1;
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unsigned int exponent:8;
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unsigned int quiet_nan:1;
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unsigned int mantissa:22;
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#endif /* Big endian. */
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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unsigned int mantissa:22;
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unsigned int quiet_nan:1;
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unsigned int exponent:8;
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unsigned int negative:1;
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#endif /* Little endian. */
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} ieee_nan;
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};
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#define IEEE754_FLOAT_BIAS 0x7f /* Added to exponent. */
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union ieee754_double
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{
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double d;
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/* This is the IEEE 754 double-precision format. */
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struct
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{
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#if __BYTE_ORDER == __BIG_ENDIAN
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unsigned int negative:1;
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unsigned int exponent:11;
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/* Together these comprise the mantissa. */
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unsigned int mantissa0:20;
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unsigned int mantissa1:32;
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#endif /* Big endian. */
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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/* Together these comprise the mantissa. */
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unsigned int mantissa1:32;
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unsigned int mantissa0:20;
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unsigned int exponent:11;
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unsigned int negative:1;
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#endif /* Little endian. */
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} ieee;
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/* This format makes it easier to see if a NaN is a signalling NaN. */
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struct
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{
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#if __BYTE_ORDER == __BIG_ENDIAN
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unsigned int negative:1;
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unsigned int exponent:11;
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unsigned int quiet_nan:1;
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/* Together these comprise the mantissa. */
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unsigned int mantissa0:19;
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unsigned int mantissa1:32;
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#else
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/* Together these comprise the mantissa. */
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unsigned int mantissa1:32;
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unsigned int mantissa0:19;
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unsigned int quiet_nan:1;
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unsigned int exponent:11;
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unsigned int negative:1;
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#endif
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} ieee_nan;
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};
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#define IEEE754_DOUBLE_BIAS 0x3ff /* Added to exponent. */
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#if __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
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/* long double is IEEE 128 bit */
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union ieee854_long_double
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{
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long double d;
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/* This is the IEEE 854 quad-precision format. */
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struct
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{
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#if __BYTE_ORDER == __BIG_ENDIAN
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unsigned int negative:1;
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unsigned int exponent:15;
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/* Together these comprise the mantissa. */
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unsigned int mantissa0:16;
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unsigned int mantissa1:32;
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unsigned int mantissa2:32;
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unsigned int mantissa3:32;
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#endif /* Big endian. */
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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/* Together these comprise the mantissa. */
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unsigned int mantissa3:32;
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unsigned int mantissa2:32;
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unsigned int mantissa1:32;
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unsigned int mantissa0:16;
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unsigned int exponent:15;
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unsigned int negative:1;
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#endif /* Little endian. */
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} ieee;
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/* This format makes it easier to see if a NaN is a signalling NaN. */
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struct
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{
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#if __BYTE_ORDER == __BIG_ENDIAN
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unsigned int negative:1;
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unsigned int exponent:15;
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unsigned int quiet_nan:1;
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/* Together these comprise the mantissa. */
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unsigned int mantissa0:15;
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unsigned int mantissa1:32;
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unsigned int mantissa2:32;
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unsigned int mantissa3:32;
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#else
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/* Together these comprise the mantissa. */
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unsigned int mantissa3:32;
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unsigned int mantissa2:32;
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unsigned int mantissa1:32;
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unsigned int mantissa0:15;
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unsigned int quiet_nan:1;
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unsigned int exponent:15;
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unsigned int negative:1;
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#endif
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} ieee_nan;
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};
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#define IEEE854_LONG_DOUBLE_BIAS 0x3fff /* Added to exponent. */
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#endif
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#if __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 0 || __GNUC_PREREQ (7, 0)
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/* IBM extended format for long double.
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Each long double is made up of two IEEE doubles. The value of the
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long double is the sum of the values of the two parts. The most
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significant part is required to be the value of the long double
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rounded to the nearest double, as specified by IEEE. For Inf
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values, the least significant part is required to be one of +0.0 or
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-0.0. No other requirements are made; so, for example, 1.0 may be
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represented as (1.0, +0.0) or (1.0, -0.0), and the low part of a
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NaN is don't-care. */
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union ibm_extended_long_double
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{
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# if __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1 && __GNUC_PREREQ (7, 0)
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__ibm128 ld;
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# else
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long double ld;
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# endif
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union ieee754_double d[2];
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};
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#endif
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__END_DECLS
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#endif /* ieee754.h */
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