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Section 13: Indirect Operations 204
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TSOLVE
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ASTO 15
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GTO IND 15
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LBLTSOLVE
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To indirectly address routines or programs outside the current program, you can use
XEQ g nn (execute indirect).
When the running program encounters an
XEQ IND nn instruction, execution is
transferred to the numeric or ALPHA label specified by the indirect address register.
The addressed program is executed as a subroutine and control returns to the main
program when execution of the subroutine is completed. For example, with the label
CIRCLE stored in R16,
XEQ g 16 causes execution of the
program defined by LBL CIRCLE. Local labels (A through J, a
through e) cannot be used indirectly with XEQ .
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Note that only programs that you write and store into program memory and those functions
contained in plug-in extensions (such as application module, or the card reader) can be
executed indirectly in this manner. Standard HP-41C functions cannot be executed with
XEQ g .
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Execution
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TCIRCLE
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LBLTCIRCLE
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ASTO 16
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XEQ IND 16
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Indirect addressing works the same way with all of the functions listed on
page 000.
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Problems
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1.
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One method of generating pseudorandom numbers in a program is to take a number
(called a ‘‘seed’’), square it, and then remove the center
of the resulting square and square that, etc. Thus, a seed of 5,182 when squared
yields 26,853,124. A random number generator could then extract the four center digits,
8,531, and square that value. Continuing for several iterations through a loop would
generate several random numbers. Following is a flowchart and programming hints for
such a pseudorandom number generator.
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The seed is a four-digit number in the form of nn.nn, .nnnn, or nnnn. The seed is
squared and the square truncated by the main part of the program, and the
resulting four-digit random number is displayed in the form of the original seed.
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