IBM SC34-5764-01, Manual

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Note: Using the LEAVE or ITERATE instructions can also modify the execution of repetitive loops.
Evaluate exprr + 0
evaluate expri + 0
exprt + 0, exprb + 0,
exprf + 0
in order written
or
and
and
Assign start value to control
variable
Use TO value (expr) to test
control variable for termination
Discontinue execution of DO
group if TO value is exceeded
Discontinue execution of DO
group if number of iterations
is exceeded
Discontinue execution of DO
group if FOR value (number of
iterations through the loop) is
exceeded
Discontinue execution of DO
group if WHILE condition is
not met
Discontinue execution of DO
group if UNTIL condition is
met
Use FOR value (exprf) to test
for termination
Use WHILE expression (exprw)
to test for termination
Use BY expression (exprb) to
update control variable
Use UNTIL expression (expru)
to test for termination
Use count of iterations (exprr)
to test for termination
Execute instruction(s)
in the DO group
Figure 49. Concept of a DO Loop
DO
Chapter 13. Keyword Instructions
141