DO loop terminator generation

This table summarizes the various instructions that are generated to terminate DO loops. The types of loops are discussed following the table, including examples.

Table 1. DO loop terminator generation
Type	Keywords¹	Other conditions	Result
Simple DO	None	ONCE or omitted	Null
Infinite loop	Neither FROM WHILE nor UNTIL	INF parameter	BC 15
Explicit specification	FROM, plus TO or BY	BXH parameter BXLE parameter	BXH BXLE
Counting	FROM (only)	Two values Three values	BCT BCTR
Backward indexing	FROM, TO and BY	FROM and TO numeric FROM value greater than TO value	BXH
Backward indexing	FROM BY	BY numeric and less than zero	BXH
Forward indexing	Any combination not covered in the above cases		BXLE
Note: The LABEL keyword may be used on any DO macro without affecting the loop terminator.