/* Total order for 'float'
Copyright 2023-2025 Free Software Foundation, Inc.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This file 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 Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Paul Eggert. */
#include <config.h>
/* Specification. */
#include <math.h>
#include <string.h>
int
totalorderf (float const *x, float const *y)
{
/* If the sign bits of *X and *Y differ, the one with non-zero sign bit
is "smaller" than the one with sign bit == 0. */
int xs = signbit (*x);
int ys = signbit (*y);
if (!xs != !ys)
return xs;
/* If one of *X, *Y is a NaN and the other isn't, the answer is easy
as well: the negative NaN is "smaller", the positive NaN is "greater"
than the other argument. */
int xn = isnanf (*x);
int yn = isnanf (*y);
if (!xn != !yn)
return !xn == !xs;
/* If none of *X, *Y is a NaN, the '<=' operator does the job, including
for -Infinity and +Infinity. */
if (!xn)
return *x <= *y;
/* At this point, *X and *Y are NaNs with the same sign bit. */
unsigned int extended_sign = -!!xs;
#if defined __hppa || (defined __mips__ && !MIPS_NAN2008_FLOAT) || defined __sh__
/* Invert the most significant bit of the mantissa field. Cf. snan.h. */
extended_sign ^= (1U << 22);
#endif
union { unsigned int i; float f; } xu = {0}, yu = {0};
#if 0
xu.f = *x;
yu.f = *y;
#else
# if defined __GNUC__ || defined __clang__
/* Prevent gcc and clang from reusing the values of *x and *y (fetched above)
in optimized inlined memcpy expansions.
Seen with gcc <https://gcc.gnu.org/PR114659>
and with clang 16.0.6 on OpenBSD 7.5. */
__asm__ __volatile__ ("" : : : "memory");
# endif
/* On 32-bit x86 processors, as well as on x86_64 processors with
CC="gcc -mfpmath=387", the evaluation of *x and *y above is done through
an 'flds' instruction, which converts a signalling NaN to a quiet NaN. See
<https://lists.gnu.org/archive/html/bug-gnulib/2023-10/msg00060.html>
for details. Use memcpy to avoid this. */
memcpy (&xu.f, x, sizeof (float));
memcpy (&yu.f, y, sizeof (float));
#endif
return (xu.i ^ extended_sign) <= (yu.i ^ extended_sign);
}
