src/LAPACK/dlaisnan.f

   1       LOGICAL FUNCTION DLAISNAN(DIN1,DIN2)
   2 *
   3 *  -- LAPACK auxiliary routine (version 3.1) --
   4 *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
   5 *     November 2006
   6 *
   7 *     .. Scalar Arguments ..
   8       DOUBLE PRECISION DIN1,DIN2
   9 *     ..
  10 *
  11 *  Purpose
  12 *  =======
  13 *
  14 *  This routine is not for general use.  It exists solely to avoid
  15 *  over-optimization in DISNAN.
  16 *
  17 *  DLAISNAN checks for NaNs by comparing its two arguments for
  18 *  inequality.  NaN is the only floating-point value where NaN != NaN
  19 *  returns .TRUE.  To check for NaNs, pass the same variable as both
  20 *  arguments.
  21 *
  22 *  Strictly speaking, Fortran does not allow aliasing of function
  23 *  arguments. So a compiler must assume that the two arguments are
  24 *  not the same variable, and the test will not be optimized away.
  25 *  Interprocedural or whole-program optimization may delete this
  26 *  test.  The ISNAN functions will be replaced by the correct
  27 *  Fortran 03 intrinsic once the intrinsic is widely available.
  28 *
  29 *  Arguments
  30 *  =========
  31 *
  32 *  DIN1     (input) DOUBLE PRECISION
  33 *  DIN2     (input) DOUBLE PRECISION
  34 *          Two numbers to compare for inequality.
  35 *
  36 *  =====================================================================
  37 *
  38 *  .. Executable Statements ..
  39       DLAISNAN = (DIN1.NE.DIN2)
  40       RETURN
  41       END