Data Representation

The FORTRAN 77 Language Reference Manual, Fortran User's Guide, and the Sun Numerical Computation Guide discuss in detail the hardware representation of data objects in Fortran. Differences between data representations across systems and hardware platforms usually generate the most significant portability problems.

The following issues should be noted:

• Sun adheres to the IEEE Standard 754 for floating-point arithmetic. Therefore, the first four bytes in a REAL*8 are not the same as in a REAL*4.

• The default sizes for reals, integers, and logicals are described in the FORTRAN 77 standard, except when these default sizes are changed by the -xtypemap= option (or by -i2, -dbl, or -r8).

• Character variables can be freely mixed and equivalenced to variables of other types, but be careful of potential alignment problems.

• f77 IEEE floating-point arithmetic does raise exceptions on overflow or divide by zero but does not signal SIGFPE or trap by default. It does deliver IEEE indeterminate forms in cases where exceptions would otherwise be signaled. This is explained in the Floating Point Arithmetic chapter of this Guide.

• The extreme finite, normalized values can be determined. See libm_single(3F) and libm_double(3F). The indeterminate forms can be written and read, using formatted and list-directed I/O statements.