fpt Reference: CHECK EQUIVALENCE

fpt and WinFPT Reference Manual - Command-line Commands

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CHECK EQUIVALENCE

Syntax:

[DO NOT] CHECK EQUIVALENCE

Function:

fpt checks for two situations:

mixed equivalence - the explicit equivalencing of objects of different data type or data size. For example, where a REAL*4 and a REAL*8 variable are declared to be equivalenced in the same sub-program;
implied equivalence, where objects with different data types, data sizes or simply with different names occupy the same addresses in COMMON blocks without any explicit equivalence statement.

Mixed equivalence is an important issue when code is ported from one system to another. The most common cases are:

the deliberate equivalencing of an INTEGER*4 variable to two INTEGER*2 variables in order to manipulate the bit pattern. This works differently on big-ended and little-ended machines;
the equivalencing of a REAL*4 to a REAL*8 variable in order to access a lower precision value of the REAL*8. This works with the default D_Float real numbers under VAX/VMS, and on Encore Concept-32 hosts. It does not work with IEEE numbers on, for example, PCs, Macintosh, RS6000 and SGI hosts.

Implied equivalence is often accidental. If two different objects occupy the same location in a COMMON block, one will overwrite the other.

By default, fpt treats objects with a declared data size, for example declared as INTEGER*4 K, as distinct from objects in which the data size is inferred from the system defaults, declared for example as INTEGER K. The equivalence check may be instructed to ignore the distinction between defaulted and explicitly declared sizes by the command EQUIVALENCE CHECK TO IGNORE DEFAULT SIZES.

Where to Use this Command

Operating system command line	Yes
Configuration file, config.fsp	Yes
Specification (fsp) files, *.fsp	Yes
Interactively, to FPT> prompt	Yes
Interactive command files	Yes
Embedded in the Fortran code	Yes

Default

The equivalence check is not carried out by default (Note that defaults may be changed in the configuration file).

Examples

Interactive use:

FPT> check equiv

fpt reports:

EQUIVALENCE Check ================= Check of COMMON Blocks ---------------------- COMMON TESS ----------- Implied EQUIVALENCE Name Sub-prog/Struct Use/COMMON Address Type Size Bounds ---- --------------- ---------- ------- ---- ---- ------ VERT TRIAD TESS 100 REAL *4 df (1:5,1:5) DEVIAT SIMPLX TESS 100 REAL *4 df SSQ SIMPLX TESS 104 REAL *4 df (1:5) ******************** Check of Local Variables for Mixed EQUIVALENCE ---------------------------------------------- Mixed type, mixed size or mis-aligned EQUIVALENCE Name Sub-prog/Struct Use/COMMON Address Type Size Bounds ---- --------------- ---------- ------- ---- ---- ------ UD TRIAD Local DOUBLE PRECISION *8 df UR TRIAD Local REAL *4 df ******************** -------------------------------------------------------------- EQUIVALENCE Check Total number of mixed or implied EQUIVALENCE (Warnings): 2 --------------------------------------------------------------