7.4 Data Representation

The Fortran User’s Guide, and the 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 95 standard, except when these default sizes are changed by the -xtypemap option.

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

• f95 IEEE floating-point arithmetic will raise exceptions on overflow or divide by zero and signal SIGFPE or trap by default (-ftrap=common is the default with f95). It does deliver IEEE indeterminate forms in cases where exceptions would otherwise be signaled. This is explained in Chapter Chapter 6, Floating-Point Arithmetic.

• 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.