> -----Original Message-----
> From: Mike Hornsby
> 
> Below are two versions of the same COBOL Prime number program. 
> The first version took 28,051 CPU Milliseconds, the final 
> version took 4,654 Milliseconds. 
> Friday's trivia question is:  What changes resulted in the 
> largest performance gains, and why?

Even before I looked, I figured one "difference" would be character-based PICs vs. "COMPUTATIONAL" -- without the "[usage] comp" clause on a PIC statement, "numeric" variables are actually stored as character sequences, and internally are prone to lots of conversions between text-and-binary representtions of the number.

BUT, since you asked "what resulted in the LARGEST gain", I take it you actually did "several" speed-enhancements -- while there may be some synergy, the only way to answer this would be to make "one change at a time" -- starting from the original:

   * make the numeric variables COMP instead of DISPLAY
   * use the FUNCTION REM(...) instead of DIVIDE REMAINDER
     - and if FUNCTION REM... is faster, fold the test into the IF 
       statement and avoid storing the intermediate, i.e., 
         IF FUNCTION REM(CALC-NO DIV-NO) = ZERO THEN...
     - OR try a level-88 on variable R, AS IN 
        05  R  PIC S9(9) COMP.
          88 NOT-A-PRIME VALUE ZERO.
        ...
        PERFORM ... UNTIL (DIV-NO > CALC-ROOT) 
                       OR NOT-A-PRIME
   * for that matter, instead of > CALC-NO + 1 / 2, your limit
     should be the square root of calc-no
   * and while you're at it, calculate the limit once instead
     of every iteration (i.e., COMPUTE CALC-ROOT = FUNCTION SQRT(CALC-NO) )
     then use as shown above
 
after you've tried each of these /STARTING FROM THE ORIGINAL EACH TIME/, try combinations of two techniques, etc.

* To join/leave the list, search archives, change list settings, *
* etc., please visit http://raven.utc.edu/archives/hp3000-l.html *