HP41C - workaround for the SIZE? missing

[Sylvain Cote]

The following program (64 bytes) will find the number of registers in nine lookup. (160, 80, 40, 20, 10, 5, 3, 2, 1)

Code:

01 LBL "SIZE?"    // Entry Point
02 SF 25          // Start with substraction
03 0              // Register index
04 320            // Register offset (startup value, max number of registers)
05 LBL 00         // Loop
06 2              //
07 /              // Divide register offset by 2
08 .5             //
09 +              // Add .5 for odd divisions
10 INT            // Get interger part
11 FS? 25         // If last memory access was valid
12 +              // Add register offset to register index
13 FC? 25         // If last memory access was invalid
14 -              // Substract register offset from register index
15 LASTX          // Get back register offset
16 SF 25          // Ignore next error
17 RCL IND Y      // Memory access request
18 FS? 25         // If successful
19 RDN            // Drop unneeded recalled value
20 1              // Exit loop condition
21 X=Y?           // 
22 GTO 01         // leave loop if the offset is 1
23 RDN            // Drop exit loop test value
24 GTO 00         // Loop for next iteration
25 LBL 01         // Almost done
26 RDN            // Drop exit loop test value
27 RDN            // Drop register offset
28 SF 25          // Ignore next error
29 RCL IND X      // Memory access request
30 FC? 25         // If last memory access was invalid
31 GTO 02         // Odd number of registers allocated, no compensation needed
32 RDN            // Drop unneeded recalled value
33 1              // Even number of registers allocated, compensation needed
34 +              // Compensate the value found by 1
35 LBL 02         // Compensation terminated
36 X<0?           // If the number is negative, thene there was no data register allocated
37 0              // 0 for no data registers
38 END            // The number of registers has been found

On a unmodified HP-41CX Halfnut, the program consistently runs in 5.7 seconds.

Measured with the stopwatch
Insert after LBL "SIZE?" -> 0, SETSW, RUNSW
Insert before END -> STOPSW, RCLSW, X<>Y

Have fun!

Sylvain

Edit: add run time