More PL/I fun (with my Z80)

I received a couple of excellent comments regarding my previous blog posts on PL/I and it’s compiler bug with double precision and the ‘**’ operator. I replaced ‘**’ with a dead simple ‘doexp()’ function that simply did serial multiplications using a loop. It was not very sophisticated, nor very efficient.

Ed suggested I search for “exp_by_squaring_iterative”, which I did. It’s a very simple and elegant recursive method for calculating y to the power x, and was easy to implement in PL/I, which supports recursion. After a quick test to prove ‘I got it right’, I replaced ‘doexp()’ with ‘powsq()’ (my name for it) in both fracture programs as well as the concentration programs.

Tests with the concentration programs proved the new method is almost twice as fast as the brute-force function, which is very rewarding.

The next problem I ended up tackling (and am still working on) turns out to be caused by the ‘weirdness’ of 2D arrays. Basically, different programming languages order arrays differently. C (and PL/I) order 2D arrays by row-column, while FORTRAN orders by column-row, when the array is populated by either BLOCK DATA (FORTRAN) or {} (c) or ‘static input ()’ (PL/I).

Figuring out that the original FORTRAN program loaded the arrays in a completely different manner than PL/I has caused me no little headache. I ended up having to debug both the FORTRAN code to see how the array was stored as well as the PL/I program.

Still, I’m having fun and still enjoying my foray into PL/I.

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