HP 3000 Manuals

HP FORTRAN 77/iX Reference

REAL*4 Format 

A REAL or REAL*4 datum is a processor approximation of a real number,
whose values can be positive, negative, or zero.

A REAL*4 datum occupies one 32-bit word in memory, in floating-point
format.  It has an approximate normalized range of:

     0.0
     and
     +-1.175494*10-38 to +-3.402823*10+38 

In addition, it has an approximate denormalized range of:

     +-1.401298*10-45 to +-1.175494*10-38 


          Figure 10-4.  REAL*4 Format 

The REAL*4 format has an 8-bit exponent and a 23-bit fraction.
Significance to the user is approximately seven decimal digits.  The sign
bit is zero for plus, 1 for minus.  The exponent field contains 127 plus
the actual exponent (power of two) of the number.  Exponent fields
containing all zeros and all ones are "reserved." If the exponent is zero
and the fraction zero, the number is interpreted as a signed zero.  If
the exponent is zero and the fraction not zero, the number is called
"denormalized." A floating-point number stored in a "normalized" form has
a binary point to the left of the fraction field and an implied leading 1
to the left of the binary point; the denormalized number does not have
this implied leading 1 to the left of the binary point.

If the exponent is all ones and the fraction is zero, the number is
regarded as a signed infinity.  If the exponent is all ones and the
fraction is not zero, then the interpretation is "not-a-number" (NaN).
Attempts to operate on infinities and NaNs cause a system trap.

MPE/iX 5.0 Documentation