Binary representation of REAL #'s VAX vs.IRIS

[Brent L. Bates AAD/TAB MS294 x42854]

   We have a 3130 and the FORTRAN manual shows how REALS and DOUBLE
PRECISION numbers are stored and I am pretty sure it is the same on
the 4D machines.  Below is that description:

   REAL and DOUBLE PRECISION data elements are represented according to
the proposed IEEE standard described in Computer magazine of March 1981.
The diagrams below illustrate the representation.

                   __________________________________________
REAL                 S     Exponent            Mantissa
                   ------------------------------------------
                    31     30    23     22                  0
                    |         |                   |
                   Sign       |         Mantissa(23 + 1 bits)
                           Exponent, biased by 127

                   __________________________________________
DOUBLE PRECISION     S     Exponent            Mantissa
                   ------------------------------------------
                    63     62    52     31                  0
                    |         |                   |
                   Sign       |         Mantissa(52 + 1 bits)
                           Exponent, biased by 1023

   The parts of REAL and DOUBLE PRECISION numbers are as follows:

 * a one-bit sign bit designated by "S" in diagrams above.  The sign
   bit is a 1 only if the number is negative.

 * a biased exponent.  The exponent is eight bits for a REAL number,
   and 11 bits for a DOUBLE PRECISION number.  The values of all zeros,
   and all ones, are reserved values for exponents.

 * a normalized mantissa, with the high-order 1 bit "hidden."  The
   mantissa is 23 bits for a REAL number, and is 52 bits for a DOUBLE
   PRECISION number.  A REAL or DOUBLE PRECISION number is represented
   by the form:

       exponent-bias
      2             x 1.fraction
   where fraction is the number of bits in the mantissa.

   Examples:
   ________________________________________
     Value       Real      DOUBLE PRECISION 
   ----------------------------------------
       +0      00000000    0000000000000000
       -0      80000000    8000000000000000

       +1      3f800000    3ff0000000000000
       -1      bf800000    bff0000000000000

       +2      40000000    4000000000000000
       +3      40400000    4008000000000000

   +Infinity   7f800000    7ff0000000000000
   -Infinity   ff800000    fff0000000000000

      NaN      7f8xxxxx    7ffxxxxxxxxxxxxx
   ----------------------------------------

   I hope this is of some help.
--

	Brent L. Bates
	NASA-Langley Research Center
	M.S. 294
	Hampton, Virginia  23665-5225
	(804) 864-2854
	E-mail: blbates at aero4.larc.nasa.gov or blbates at aero2.larc.nasa.gov