The REAL(4) (IEEE* S_floating), REAL(8) (IEEE T_floating), and REAL(16) (IEEE-style X_floating) formats are stored in standard little endian IEEE binary floating-point notation. (See IEEE Standard 754 for additional information about IEEE binary floating point notation.) COMPLEX() formats use a pair of REAL values to denote the real and imaginary parts of the data.
All floating-point formats represent fractions in sign-magnitude notation, with the binary radix point to the right of the most-significant bit. Fractions are assumed to be normalized, and therefore the most-significant bit is not stored (this is called "hidden bit normalization"). This bit is assumed to be 1 unless the exponent is 0. If the exponent equals 0, then the value represented is denormalized (subnormal) or plus or minus zero.
Intrinsic REAL kinds are 4 (single precision), 8 (double precision), and 16 (extended precision), such as REAL(KIND=4) for single-precision floating-point data. Intrinsic COMPLEX kinds are also 4 (single precision), 8 (double precision), and 16 (extended precision).
To obtain the kind of a variable, use the KIND intrinsic function. You can also use a size specifier, such as REAL*4, but be aware this is an extension to the Fortran 95 standard.
If you omit certain compiler options, the default sizes for REAL and COMPLEX data declarations are as follows:
For REAL data declarations without a kind parameter (or size specifier), the default size is REAL (KIND=4) (same as REAL*4).
For COMPLEX data declarations without a kind parameter (or size specifier), the default data size is COMPLEX (KIND=4) (same as COMPLEX*8).
To control the size of all REAL or COMPLEX declarations without a kind parameter, use the -real_size 64 or -real_size 128 options; the default is -real_size 32.
You can explicitly declare the length of a REAL or a COMPLEX declaration using a kind parameter, or specify DOUBLE PRECISION or DOUBLE COMPLEX. To control the size of all DOUBLE PRECISION and DOUBLE COMPLEX declarations, use the -double_size 128 option; the default is -double_size 64.
The following sections discuss floating-point data:
For information on reading or writing floating-point data other than native IEEE little endian data, see Converting Unformatted Numeric Data.
See also File fordef.for and Its Usage and Using the Floating Point Exception Handling (-fpe) Option.