1  /* Return positive difference between arguments.  i386 version.
       2     Copyright (C) 1997-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <errno.h>
      20  #include <fpu_control.h>
      21  #include <math.h>
      22  #include <math-narrow-eval.h>
      23  #include <libm-alias-double.h>
      24  
      25  double
      26  __fdim (double x, double y)
      27  {
      28    if (islessequal (x, y))
      29      return 0.0;
      30  
      31    /* To avoid double rounding, set double precision for the
      32       subtraction.  math_narrow_eval is still needed to eliminate
      33       excess range in the case of overflow.  If the result of the
      34       subtraction is in the subnormal range for double, it is exact, so
      35       no issues of double rounding for subnormals arise.  */
      36    fpu_control_t cw, cw_double;
      37    _FPU_GETCW (cw);
      38    cw_double = (cw & ~_FPU_EXTENDED) | _FPU_DOUBLE;
      39    _FPU_SETCW (cw_double);
      40    double r = math_narrow_eval (x - y);
      41    _FPU_SETCW (cw);
      42    if (isinf (r) && !isinf (x) && !isinf (y))
      43      __set_errno (ERANGE);
      44  
      45    return r;
      46  }
      47  libm_alias_double (__fdim, fdim)