6.7.2 C*$* storage order (var-list)

The storage order directive specifies the relative order that storage should be allocated for the listed routine-local variables and arrays. By appropriately positioning the arrays, cache collisions can be reduced. If the compiler does not interpret the storage order directive, a loss of performance results, but the program will nonetheless generate the correct results.

The rules governing the use of the C*$* storage order directive are as follows:

• More than one storage order directive may be used within a single program unit. Each directive may be interpreted separately.

• The storage order directives will be placed immediately after the PROGRAM statement or, if there is no PROGRAM statement, before the first statement of the program unit.

• An object listed in a storage order must be local to the program unit.

• An object listed in a storage order must not be:

  • Mentioned in another storage order directive

  • An element of a COMMON block

  • A dummy argument to the procedure or function

• Variables and arrays whose values are retained between procedure or function invocations (for instance, by being in SAVE statements) may not be included in the same storage order directive with variables and arrays that are not.

• Only one object from an EQUIVALENCE class may be included in storage order directives.

• KAP may generate as many C*$* storage order directives as it considers useful. Specifically, the number will not necessarily be limited to two (for saved and non-saved variables).

• Specific implementations may place additional restrictions on the storage order directive.

To interpret a C*$* storage order directive, the compiler must place the named objects in memory in the order listed. This is the same order as they would be placed in a COMMON block. For example, on a machine with 4 bytes per REAL variable:

   C*$* storage order (A1,A2,A3)
      REAL A1(100), A2(3), A3(200)

 A1 would be placed at some address (for example, address X)
 A2 would be placed at X+100*4
 A3 would be placed at X+100*4+3*4

Both static and stack-based storage schemes are allowed, as long as all of the objects in a single storage order directive are placed in the same scheme.

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