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Advanced Programming and Operation
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There are several features on the HP-41C that offer significant
power and convenience in the operation of the calculator. As you become
more interested in the HP-41C and how it works, you may wish to know
more specifically how some features work.
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Label Searching
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Earlier in this handbook it was mentioned that the HP-41C could remember the
location of most labels in program memory. More specifically, the HP-41C has
been designed to remember the location of all labels depending on
their location in a program and how they are used. The calculator can only
remember a numeric label location after the first execution of that
label. Subsequent branches to that label are much faster because the HP-41C
does not need to search (in most cases).
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Labels 00 through 14 are called short form labels. They use only a single byte
in program memory (there are seven bytes per register). When a program
branches to LBL 00 through LBL
14 using a GTO instruction, the calculator can
remember the location of these labels if they are located 112 bytes before or
after the GTO instruction. If the short form label is
beyond 112 bytes from the GTO , the calculator must
search sequentially for that label. So if you are concerned about the speed of
execution, you should examine your program and determine the location of
branches and corresponding labels.
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Labels 15 through 99, on the other hand, are not short form labels. They
require two bytes in program memory. However, the location of these labels is
always remembered by the calculator, regardless of their location in
a program.
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The location of all numeric labels ( LBL 00 through
LBL 99) is remembered by the calculator when the
program branches using XEQ .
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The HP-41C handles branches to ALPHA labels in a unique way. As soon as an
ALPHA label is keyed into a program, the calculator records that label and its
location in such a way that each ALPHA label knows where the next ALPHA label is
located. A GTO or XEQ of an
ALPHA label then causes the HP-41C to search from ALPHA to ALPHA label for the
ALPHA name. The HP-41C then branches to the corresponding location in program
memory. The ALPHA label search is from the bottom-most program in program
memory to the top-most program. The result is a search of the last programs first.
This ALPHA label search scheme increases the speed of execution by decreasing
search time.
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