Conditional Instructions - HP -32S Owner's Manual

Conditional Instructions
Another way to alterthe sequenceof program execution is by a condi
tional test, a true/false test that compares two numbers and skips the
next program instruction if the proposition is false.
For instance, if a conditional instruction on line A05 is x=0? (that is,
is x equal to zero?), then the program compares the contents of the X-
register with zero. If the X-register does contain zero, then the
program goes on to the next line. If the X-register does not contain
zero, then the program skips the next line, thereby branching to line
A07. This rule is commonly known as "Do if true."
Do if true R01 LBL R Skip if false
R05 x=G? ,_^
R96 GTO B j
R07 LN ,-J
| R08 STO R
* i |
to LBL B
The example above points out a common technique used with condi
tional tests: the line immediately after the test (which is only executed
in the 'true* case) is a branch to another label. So the net effect of the
test is to branch to a different routine under certain circumstances.
There are three categories of conditional instructions:
• Comparison tests. These compare the X- and Y-registers, or the X-
regjster and zero.
• Flag tests. These check the status of flags, which can be either set
or clear.
• Loop counters. These are usually used to loop a specified number
of times.
6: Programming Techniques 95