A few days ago someone asked, if there is a way, to generate random numbers in a CL program or procedure.
Of course it would be a lot easier to use embedded SQL and the RANDOM() function in RPG or COBOL, but he explicitly wanted CL. He needed (pseudo) random numbers between 1 and 1000.
IBM i has a suite of crypto APIs – and one of them is QC3GENRN (or Qc3GenPRNs in ILE) to generate pseudo random binary data. The prototype for the API in RPG looks like this:
/include qsysinc/qrpglesrc,qusec dcl-pr QC3GENRN extpgm('QC3GENRN'); prnData char(1000) options(*varsize); prnDataLen int(10:0) const; prnType char(1) const; prnParity char(1) const; errorCode likeds(qusec); end-pr;
- prnData – output – the „resulting“ pseudo random binary data after the API call
- prnDataLen – input – how many bytes of pseudo random data should be created
- prnType – input
- ‚0‘ = generate real pseudo random data
- ‚1‘ = generate test data with preset values for key and seed
- prnParity – input
- ‚0‘ = do not use parity
- ‚1‘ = set each byte to odd parity
- ‚2‘ = set each byte to even parity
- errorCode – input/output – the usual QUSEC errorCode data structure, which in the simpliest form is structured like this
- int(10:0) – input – size of the provided data structure – if this is set to zero, no exception id is returned, and the exception is sent to the calling program – in the simplest form you can just use an 4-byte integer variable with value zero instead of a real data structure
- int(10:0) – output – bytes of data available after the call
- char(7) – output – the exception id (message id like ‚CPF1234‘)
- char(1) – output – reserved
- char(*) – output – exception message data
So how is this API callable from CL? Lets see the code:
The parameters and the call to QC3GENRN is pretty straight forward. After the call, we have 4 bytes of pseudo random binary data in the &data variable. To use that data, we have to convert it first.
- We use %binary(...) to convert the binary data to a number – 4 bytes means, we can use a 4 byte integer.
- Integer variables are signed – so we can receive negative values – if the value is below zero, we multiply with -1, because CL has no absolute function like SQL or RPG
- We wanted numbers between 1-1000, and because CL also has no modulus or remainder function, we need to do that by integer dividing by 1000 …
- … and subtraction the result multiplied with 1000 from our original number. The remainder should now be a number between 0 and 999.
- So in the last step we add 1 to the remainder and we have numbers between 1 and 1000.
I hope you will find this little experiment useful, and of course I appreciate your comments.
P.S.: Here is the code ready for copy and paste:
pgm /* QC3GENRN API parameters */ dcl var(&data) type(*char) len(4) value(' ') dcl var(&datalen) type(*int) len(4) value(4) dcl var(&type) type(*char) len(1) value('0') dcl var(&parity) type(*char) len(1) value('0') dcl var(&qusec) type(*int) len(4) value(0) /* some working vars */ dcl var(&work1) type(*int) len(4) value(0) dcl var(&work2) type(*int) len(4) value(0) /* result - random number 1-1000 */ dcl var(&random) type(*dec) len(4 0) value(0) /* call API */ call pgm(QC3GENRN) parm(&data &datalen &type &parity &qusec) /* convert binary random data to decimal 0 - 999 */ chgvar var(&work1) value(%binary(&data 1 4)) if cond(&work1 *lt 0) then(chgvar var(&work1) value(&work1 * -1)) chgvar var(&work2) value(&work1 / 1000) chgvar var(&work1) value(&work1 - (&work2 * 1000)) /* set result variable to range 1 - 1000 */ chgvar var(&random) value(&work1 + 1) endpgm