Branching - HP -25 Owner's Handbook Manual

Overflow Calculations. Your HP-25 has been designed so
that by looking at the display you can always tell why the cal-
culator stops. If program execution stops because the result of
a calculation in the X-register is a number with a magnitude
greater than 9.999999999 x 10%, all 9's are displayed with ap-
propriate sign. It is then easy to determine the operation that
caused the overflow by switching to PRGM mode and identi-
fying the keycode in the display.
If the overflow occurs in one of the storage registers, possibly
the result of storage register arithmetic or the summations with
,the calculator will display to inform you of the over-
flow. Check the storage registers to see in which register the
overflow has occurred.
If the result of a calculation is a number with a magnitude less
than 109, zero will be substituted for the number and a running
program will continue to execute normally.
Improper Operation Stops. Calculations that cause the word
to be displayed also stop program execution. You can
identify the reason for the stop by switching momentarily to
PRGM mode to see the keycode of the improper operation. A
list of improper operations can be found in appendix B.
Branching
Although program execution is normally sequential, with one
step executed after another, execution can be transferred or
"'branched'' to any step in program memory. The ''branch' can
be made unconditionally or it can be made dependent on the
outcome of a comparison of data values.
Unconditional Branching
You have seen how [ is used in manual RUN mode to help
youdisplay any step in program memory. As an instruction exe-
cuted in a program [§[gis used to branch program execution to
the step number specified. It can tell the calculator to execute
step 00 next, as we have already seen,or to execute any other
step in program memory.