lib/totalorderf.c

   1 /* Total order for 'float'
   2    Copyright 2023-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation, either version 3 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Paul Eggert.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include <math.h>
  23
  24 int
  25 totalorderf (float const *x, float const *y)
  26 {
  27   /* If the sign bits of *X and *Y differ, the one with non-zero sign bit
  28      is "smaller" than the one with sign bit == 0.  */
  29   int xs = signbit (*x);
  30   int ys = signbit (*y);
  31   if (!xs != !ys)
  32     return xs;
  33
  34   /* If one of *X, *Y is a NaN and the other isn't, the answer is easy
  35      as well: the negative NaN is "smaller", the positive NaN is "greater"
  36      than the other argument.  */
  37   int xn = isnanf (*x);
  38   int yn = isnanf (*y);
  39   if (!xn != !yn)
  40     return !xn == !xs;
  41   /* If none of *X, *Y is a NaN, the '<=' operator does the job, including
  42      for -Infinity and +Infinity.  */
  43   if (!xn)
  44     return *x <= *y;
  45
  46   /* At this point, *X and *Y are NaNs with the same sign bit.  */
  47
  48   unsigned int extended_sign = -!!xs;
  49 #if defined __hppa || defined __mips__ || defined __sh__
  50   /* Invert the most significant bit of the mantissa field.  Cf. snan.h.  */
  51   extended_sign ^= (1U << 22);
  52 #endif
  53   union { unsigned int i; float f; } volatile xu = {0}, yu = {0};
  54   xu.f = *x;
  55   yu.f = *y;
  56   return (xu.i ^ extended_sign) <= (yu.i ^ extended_sign);
  57 }