Re: Floating point conversion

It falls back on the random number issue.....

OK, so you want to convert the 8F coming from CEERAN0 to an integer. The idea behind CEERAN0 is that is returns a floating point number between 0 and a number very near (but not touching) 1. There's more to it, but that's the part you're interested in at the moment.

So your job is to map this infinite number space to a finite set of integers. The good news is that this has been done before :-) There are a variety of ways to do this. You can think of those random numbers as occurring in ranges:

.00001 to .10000
.10001 to .20000 and so on. You could use a select/when group to bin the range into an integer; this particular binning would result in integers from 1 to 10. Or 0 through 9. Or 21 through 30. Whatever you choose to put in your EVAL inside the WHEN.

when float <= .10000
eval rnd = 1
when float <= .20000
eval rnd = 2

It'll be hard to make a generic routine out of those comparisons, but it's easier to understand how the numbers are distributed by performing this mental exercise.

If you wanted integers between 1 and 10, and you're getting numbers between 0 and .99999 (etc) then you can see that you need to multiply the float in order to scale it up where you want it. A few minutes noodling with a calculator will show that simply multiplying by 10 will get you numbers between 0 and 9.9999. In RPG, we need to consider intermediate precision: read the fine manual!!!!! One formula that can help is:

callp ceeran0(seed: float: *omit)
rnd = (%dech(float:63:62) * max) + 1

The %DECH converts the float to a number that has a real lot of decimal places, which preserves as much of the original distribution of the floats as possible. Multiplying it by the maximum number (10) will scale that tiny decimal between 0 and (almost) MAX. Adding 1 will move the entire scaled range up one full integer from 1 to MAX.

This is all you need if your range is between 1 and some other positive integer. If you need a different minimum, you'll need to throw away numbers lower than any returned by this algorithm and generate a new one.

100000 passes of this algorithm resulted in this distribution from 1-10:
(1) 10037
(2) 9782
(3) 10064
(4) 10106
(5) 9909
(6) 10020
(7) 10015
(8) 10010
(9) 9926
(10) 10131

Hope that helped some. Be careful of the seed you choose; if you choose the same seed (like a constant) you will generate the exact same sequence of random numbers every time, and that's the way it's supposed to work. By using an intial seed of zero, CEERAN0 will use a seed derived from UTC (Universal Time Coordinated.) http://publib.boulder.ibm.com/iseries/v5r2/ic2924/index.htm?info/apis/CEERAN0.htm
--buck