Finding MSB in an array

[CoderByNature]

Hey all, pretty new to PLC and got a question regarding finding the MSB or the last non-zero bit in a SINT array in studio5000...

I am reading an RFID tag in a SINT array and then copying that data into my RFID.Data string. I was wondering if there was a way to find the length of that data in the SINT array so I can use that as my RFID.Len so that the length of the string is only as long as the data I am reading.

Also wondering if it would be easier to leave the length of the string long on purpose and then just truncate any '$00' values, i also do not know how to do that.

 

[drbitboy]

FSC?

Or binary search:

MSB

Invariant: sintval < 128; sintval.[hi] bit value is 0; hi starts as 7 and hi > msb.

1. LES sintval 0 MOV 7 msb => exit
2. MOV mid 16 mid MOV msb 4
3. BST GEQ sintval mid MUL mid 4 midtmp ADD msb 2 msb NXB LES sintval mid DIV mid 4 midtmp SUB msb 2 msb BND MOV midtmp mid
4. BST GEQ sintval mid MUL mid 2 midtmp ADD msb 1 msb NXB LES sintval mid DIV mid 2 midtmp SUB msb 1 msb BND MOV midtmp mid
5. LES sintval mid SUB msb 1 msb

LENGTH of null-terminated string in SINT

N.B. assumes entire string is all elements in SINT array from sintarray[0] to up to last element before first $00, and all elements after first $00 are also $00

Invariant: sintarray[hi] is $00

1. MOV 0 lo MOV L hi MOV L mid ;;; L is length of SINT array
2. OTR mid.0 DIV mid 2 mid ADD lo mid mid
3. NEQ sintarray[mid] 0 MOV mid lo
4. EQU sintarray[mid] 0 MOV mid hi
5. SUB hi lo mid
6. GRT mid 1 JMP 2.
7. MOV hi RFID.Len

I think those two algorithms are correct, but it is rare to get right on the first try (cf. here), so they might just be close.

 

[CoderByNature]

Thank you for the help! I looked into FSC and it does what I was need it to do. Do you happen to know anything about shifting strings up or down an array?