IEEECK is called from the ILAENV to verify that Infinity and
 possibly NaN arithmetic is safe (i.e. will not trap).

ISPEC

          ISPEC is INTEGER
          Specifies whether to test just for infinity arithmetic
          or whether to test for infinity and NaN arithmetic.
          = 0: Verify infinity arithmetic only.
          = 1: Verify infinity and NaN arithmetic.

ZERO

          ZERO is REAL
          Must contain the value 0.0
          This is passed to prevent the compiler from optimizing
          away this code.

ONE

          ONE is REAL
          Must contain the value 1.0
          This is passed to prevent the compiler from optimizing
          away this code.
  RETURN VALUE:  INTEGER
          = 0:  Arithmetic failed to produce the correct answers
          = 1:  Arithmetic produced the correct answers

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