HP HP-16C - Section 9: Program Branching and Controls; Loop Control with Counters: DSZ and ISZ; Conditional Branch with DSZ or ISZ

88 Section 9: Program Branching and Controls
Indirect Branching Using the Index Register
By placing an index value in R; (the Index register), you can
indirectly branch to a location ([GTO] [1]) and indirectly call a
subroutine ( ).
These functions will transfer execution to the label that
corresponds to the absolute value of the number in the Index
register according to the table below.* (In Floating Point mode,
only the integer portion of the number in R; is used.) There are 16
possible labels: 0to9and Ato F.
For instance, if the Index register contains -14,, ([STATUS]: 2-08-
0000), then a instruction would transfer program
execution to E (|—14,9| = Eqp).
Indirect Branching
If R; Contains: [GTO) (I or wnll
transfer execution to:
0 (O16) (LBL]O
9 (916) 9
10 (A1e) (LBLJA
15 (F1e) F
Conditional Tests
Another way to alter the sequence of program execution is by a
conditional test, a true/false test which compares the number in
the X-register either to zero or to the number in the Y-register. (In
1’s Complement mode, these tests consider -0 equal to 0.)
The HP-16C provides eight different tests (all [g]-shifted
functions):
(x<y] (x<0] [x>y] [x>0] [x#y] [x#0] [x=y] [x=0
Following a conditional test, program execution follows the “Do if
True” rule: it proceeds sequentially if the condition is true, and it
skips one instruction if the condition is false. A instruction is
*The absolute value is computed using a word size of 68 and the current complement
mode.