Marc Niegowski Systems Programmer Consultant - 370, 390, z Assembler Let It Do Your Work

Recently, (August 2001) I read an article entitled "Assembler Programming Revisited" by a systems programmer from whom I have learned much and for whom I have a great deal of respect.

In this article, however, I disagree with him strongly. He cites an example where one might need to define a print line as 0CL133 and in doing so, incorrectly define the 133 bytes that must follow. If you define fewer than 133 bytes within the scope of the 0CL133, fields following the 0CL133 can potentially be overlaid.

This systems programmer suggests that you should "pad" the 0CL133 with perhaps an extra 30 bytes or so. To use that systems programmer's expression, with all due respect. . ."malarkey!"

The correct way to ensure that your print line (or any other data area consisting of multiple fields) occupies as many bytes as you intended, is to let the assembler do it for you.

WORKDS DSECT , Working Storage DSECT. . . . PRINTLN DS CL133 Print line. ORG PRINTLN Set Origin to start of line. PRLNCC DS C Print line CC. SPACE , PRNTLN1 EQU * Report Line 1. ORG *+4 4 Byte Margin. PRL1FL1 DS CL8 8 Byte Field 1. ORG *+4 4 Byte Margin. PRL1FL2 DS CL16 16 Byte Field 2. ORG *+4 4 Byte Margin. PRL1FL3 DS CL12 12 Byte Field 3. SPACE , ORG PRINTLN+1 PRNTLN2 EQU * Report Line 2. ORG *+4 4 Byte Margin. PRL2FL1 DS CL80 80 Byte Field 1. ORG *+4 4 Byte Margin. PRL2FL2 DS CL8 8 Byte Field 2. ORG *+4 4 Byte Margin. PRL2FL3 DS CL8 8 Byte Field 3. ORG *+4 4 Byte Margin. PRL2FL4 DS CL8 8 Byte Field 4. SPACE , ORG PRINTLN+1 PRNTLN3 EQU * Report Line 3. ORG *+4 4 Byte Margin. PRL3FL1 DS CL2 2 Byte Field 1. ORG *+4 4 Byte Margin. PRL3FL2 DS CL2 2 Byte Field 2. ORG *+4 4 Byte Margin. PRL3FL3 DS CL12 12 Byte Field 3. ORG *+4 4 Byte Margin. PRL3FL4 DS CL6 6 Byte Field 4. ORG *+4 4 Byte Margin. PRL3FL5 DS C 1 Byte Field 5. ORG , Reset Origin. SPACE , WORKFL1 DS XL5 Any work field(s). . . . * End of DSECT.

In the above example, three different report lines redefine the report line buffer named PRINTLN.

Before you move any data to the report line fields, you should initialize the report line to blanks as follows:

INITPL DS 0H Initialize the report line. MVI PRLNCC,X'40' Set the first byte to a blank. MVC PRLNCC+1(L'PRINTLN-1),PRLNCC Clear entire area.