Compression-time invocation of IRRACX01

In non-cross-memory environments, IRRACX01 gets control before compression of an ACEE if ACEEIEP is nonzero. The compression function chooses which data (if any) is to be compressed with the ACEE, based on what IRRACX01 returns:

If IRRACX01 returns no range table and if ACEEIEP is still nonzero, RACF® assumes that it points to a standard ACEEIEP data area and compresses that data along with the ACEE.
When the ACEE is expanded later, RACF expands this data automatically, without calling IRRACX01 again. IRRACX01 should be careful about making changes to ACEEIEP or the data it points to, as such changes affect the original, uncompressed ACEE.
If IRRACX01 returns a range table, the compression function ignores the contents of the ACEEIEP field and compresses only the data indicated by the range table. IRRACX01 returns a range table by setting a pointer to it at offset X'8' into the exit parameter list.