Lahey/GNU Fortran

-[n]dbl

Double

Compile only. Default: -ndbl

GFortran option: -fdefault-real-8

Specify -dbl to extend all single-precision REAL and single-precision COMPLEX variables, arrays, constants, and functions to 64 bit double-precision. If you use -dbl, all source files (including modules) in a program should be compiled with -dbl. Specifying -dbl may or may not result in a somewhat slower executable.