The format of a COMP-4 item is two's-complement binary. COMP-4 values are stored in a machine-independent format. This format places the highest-order part of the value in the leftmost position and follows down to the low-order part in the rightmost position. The number of bytes a data item occupies depends on the number of "9"s in its PICTURE and on the presence of various compile-time options. This is summarized in the following table:
The format of a COMP-5 data item is identical to a COMP-4 data item, except that the data is stored in a machine-dependent format. It is stored in an order that is natural to the host machine. For example, a PIC S9(4) COMP-5 data item is equivalent to a 16-bit binary word on the host machine, and a PIC S9(9) COMP-5 item is equivalent to a 32-bit word. Note that data stored in a COMP-5 field may not be transportable to other machines because different machines have different natural byte-orderings. On many machines (68000, most RISC), COMP-5 is identical to COMP-4. On others (80x86, VAX), it is the same with the bytes in the reverse order.
COMP-5 is primarily used to communicate with external programs that expect native data storage. A VALUE clause for a COMP-5 data item is stored in a machine-independent format and is adjusted when it is loaded into the data item. This ensures that the value is the same from machine to machine.
Level 01 and level 77 data items that are COMP-5 are automatically synchronized to an appropriate machine boundary, regardless of any compile-time settings. This allows you to pass these items safely to C subroutines without having to concern yourself with alignment.
The format of a COMP-6 item is identical to a COMP-3 item except that it is unsigned and no space is allocated for the sign. Thus there are two decimal digits per byte, and the actual size of the item is determined by dividing its PICTURE size by two and rounding up.
About Level 76 & 78, will get back to you on this.
