lib/getpayloadf.c

   1 /* Extract the payload of a NaN 'float'.
   2    Copyright 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 Bruno Haible.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include <math.h>
  23
  24 #include <float.h>
  25 #include <stdint.h>
  26 #include <string.h>
  27
  28 float
  29 getpayloadf (const float *value)
  30 {
  31   if (isnanf (*value))
  32     {
  33 #if FLT_MANT_DIG == 24
  34       union { uint32_t i; float f; } x;
  35 # if 0
  36       x.f = *value;
  37 # else
  38       /* On 32-bit x86 processors, as well as on x86_64 processors with
  39          CC="gcc -mfpmath=387", the evaluation of *value above is done
  40          through an 'flds' instruction, which converts a signalling NaN to
  41          a quiet NaN. See
  42          <https://lists.gnu.org/archive/html/bug-gnulib/2023-10/msg00060.html>
  43          for details.  Use memcpy to avoid this.  */
  44       memcpy (&x.f, value, sizeof (float));
  45 # endif
  46       int32_t payload = x.i & (((uint32_t) 1 << (FLT_MANT_DIG - 2)) - 1);
  47       return payload;
  48 #else
  49 # error "Please port gnulib getpayloadf.c to your platform!"
  50 #endif
  51     }
  52   else
  53     return -1.0f;
  54 }