HP 3000 Manuals

HP FORTRAN 77/iX Reference

REAL*8 Format 

A REAL*8 or DOUBLE PRECISION datum is a processor approximation to a real
number, whose values can be positive, negative, or zero.

A REAL*8 datum occupies two consecutive 32-bit words in memory in
floating-point format.  It has an approximate normalized range of:

     0.0
     and
     +-2.225073858507202*10-308 to +-1.797693134862315*10+308 

In addition, it has an approximate denormalized range of:

     +-4.940656458412466*10-324 to +-2.225073858507201*10-308 


          Figure 10-5.  REAL*8 Format 

A REAL*8 datum is 64-bit-aligned; that is, its address is divisible by
eight.

The REAL*8 format has an 11-bit exponent and a 52-bit fraction.
Significance to the user is approximately 16 decimal digits.  The sign
bit is zero for plus, one for minus.  The exponent field contains 1023
plus the actual exponent (power of 2) 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; a 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 denormalized numbers, infinities, and NaNs cause a
system trap.

MPE/iX 5.0 Documentation