Determining the amount of SPOOL space used by SPOOLed $JCT extensions

The length of a $JCT extension is limited by the size of the $JCT control block and an installation's spool buffer size. IBM provides 512 bytes in the spool buffer, in addition to anything beyond the smallest buffer size available (1944 bytes). The buffer size is specified on the BUFDEF= parameter of the SPOOLDEF initialization statement. Use the algorithm in the following figure to determine how much space is used by $JCT control block extensions within a $JCT control block:

Figure 1. Determine the Amount of Spool Space Used by $JCTX Extensions

$BUFSIZE (JCT buffer) - JCTFEND-JCTSTART (Fixed $JCT) - JCTRXLEN (space left)
 = Space used by JCT extensions in this $JCT

The following assembler instructions use this formula:

        LH     R1,$BUFSIZE             Get spool buffer size
        SH     R1,=Y(JCTFEND-JCTSTART) Subtract size of fixed portion
                                       of the JCT
        SH     R1,JCTRXLEN             Subtract amount of unused space

To determine the amount of space that remains in this $JCT control block for extensions, specify:

        LH    R1,JCTRXLEN