The SELECT macro set

The SELECT macro set selects one of a set of functions for execution, depending on the result of a comparison. The flowchart for the SELECT program figure is:

        ┌──────┐     ┌────────┐ True  ┌────┐
 ──────→┤SELECT├────→┤WHEN (1)├──────→┤ F1 ├──→──────────┐
        └──────┘     └───┬────┘       └────┘             │
                         │                               ↓
                         │ False                         │
                         ↓                               │
                     ┌───┴────┐ True  ┌────┐             │
                     │WHEN (2)├──────→┤ F2 ├──→──────────┤
                     └───┬────┘       └────┘             │
                         │ False                         ↓
                         ↓                               │
                     ┌───┴────┐ True  ┌────┐             │
                     │WHEN (3)├──────→┤ F3 ├──→──────────┤
                     └───┬────┘       └────┘             │
                         │ False                         ↓
                         │                               │
                         .                               .
                         .                               .
                         ↓                               .
                     ┌───┴────┐ True  ┌────┐
                     │WHEN (n)├──────→┤ Fn ├──→──────────┤
                     └───┬────┘       └────┘             │
                         │ False                         │
                         ↓                               ↓
                    ┌────┴────┐       ┌─────┐        ┌───┴──┐
                    │ OTHRWISE├──────→┤Code ├───────→┤ENDSEL├─→
                    └─────────┘       └─────┘        └──────┘

OTHRWISE is optional.

This example uses the SELECT, WHEN, OTHRWISE, and ENDSEL macros:

        SELECT CLI,0(R6),EQ           Defines the comparison
          WHEN  (X'20')
            Code for F1
          WHEN  (1,5,13)
            Code for F2
          WHEN  (3,7,15)
            Code for F3
          OTHRWISE
            Code for F4
        ENDSEL

It produces:

        SELECT CLI,0(R6),EQ           Defines the comparison
           WHEN  (X'20')
          CLI   0(R6),X'20'
          BC    15-8,#@LB2
          Code for F1
           WHEN  (1,5,13)
          BC    15,#@LB1               SKIP TO END
#@LB2     DC    0H
          CLI          0(R6),1
          BC    8,#@LB5
          CLI          0(R6),5
          BC    8,#@LB5
          CLI          0(R6),13
          BC    15-8,#@LB4
#@LB5     DC    0H
           Code for F2
           WHEN  (3,7,15)
          BC    15,#@LB1               SKIP TO END
#@LB4     DC    0H
          CLI          0(R6),3
          BC    8,#@LB7
          CLI          0(R6),7
          BC    8,#@LB7
          CLI          0(R6),15
          BC    15-8,#@LB6
#@LB7     DC    0H
           Code for F3
           OTHRWISE
          BC    15,#@LB1               SKIP TO END
#@LB6     DC  0H
           Code for F4
         ENDSEL
#@LB1    DC     0H

Here is another example of the SELECT Macro Set:

        SELECT CLM,2,B'1100',EQ
        WHEN (=C'AA',=C'BB')
          Process A
        WHEN =C'AB'
          Process B
        WHEN =C'12'
          Process C
        ENDSEL

It produces:

          CLM   2,B'1100',=C'AA'
          BC    8,LB3
          CLM   2,B'1100',=C'BB'
          BC    15-8,LB2
 LB3      DC    0H
            Process A
          B     LB1
 LB2      DC    0H
          CLM   2,B'1100',=C'AB'
          BC    15-8,LB4
            Process B
          B     LB1
 LB4      DC    0H
          CLM   2,B'1100',=C'12'
          BC    15-8,LB6
            Process C
 LB6      DC    0H
 LB1      DC    0H

The SELECT group allows a SELECT with no operands followed by WHEN macros with IF style operands. This produces the same structure as the IF/ELSEIF/ELSE/ENDIF macros.

For example: :

        SELECT
        WHEN (CLI,WORD1,EQ,1),OR,(CLI,WORD1,EQ,2),OR,(CLI,WORD1,EQ,3)
           <code for first condition>
        WHEN (CLI,WORD2,EQ,2),AND,(CLI,WORD3,EQ,3)
           <code for second condition>
        OTHRWISE
           <otherwise  code>
        ENDSEL

produces (assuming that ASMMREL ON has been coded earlier):

        SELECT
        WHEN (CLI,WORD1,EQ,1),OR,(CLI,WORD1,EQ,2),OR,(CLI,WORD1,EQ,3)
          CLI   WORD1,1
          BRC   8,#@LB3
          CLI   WORD1,2
          BRC   8,#@LB3
          CLI   WORD1,3
          BRC   15-8,#@LB2
#@LB3     DC    0H
           <code for first condition>
        WHEN (CLI,WORD2,EQ,2),AND,(CLI,WORD3,EQ,3)
          BRC   15,#@LB1               SKIP TO END
#@LB2     DC  0H
          CLI   WORD2,2
          BRC   15-8,#@LB4
          CLI   WORD3,3
          BRC   15-8,#@LB4
           <code for second condition>
        OTHRWISE
          BRC   15,#@LB1               SKIP TO END
#@LB4     DC    0H
           <otherwise  code>
        ENDSEL
#@LB1     DC    0H