Section 14,59: double-precision_constant

 double-precision constant

 A processor approximation to the value of a real number that
 occupies 8 bytes of memory and can assume a positive, negative, or
 zero value.  The precision is greater than a constant of real
 (single-precision) type.  On VAX and VMS on AXP processors, the
 range for D_floating is approximately 0.29D-38 to 1.7D38; for
 G_floating, approximately 0.56D-308 to 0.9D308.  On RISC and Alpha
 AXP processors, the range for T_floating is approximately
 2.225D-308 to 1.798D308.  See also denormalized_number.