Floating point math in FORTRAN IV on PDP-8

[Rick Murphy]

On 9/19/2018 6:43 PM, Kyle Owen via cctalk wrote:
> At VCF MW this past weekend, I was playing around with an FPP8/A stuffed
> into a PDP-8/M with a fan removed. This hex-wide two-board set will happily
> work in a quad-wide backplane, as it needs no signals that an 8/A would
> otherwise provide.
>
> I wanted to benchmark the FPP8/A with the software emulation that FORTRAN
> IV supposedly does. Mind you, I also don't have an EAE in mine, so software
> emulation for integer multiplication/division would also be used.
>
> I tried running a simple program to print some natural logs and square
> roots, which ran quite well with the FPP8/A in place.
>
> Without the FPP8/A...all of the results were wrong. Significantly. Negative
> numbers in many cases. No clear pattern as to what it's doing.

That seems like you have a mixed-up F4 compiler/runtime.
On my system (SIMH) I get the same results, FPP enabled or disabled. 
Don't know how to enable/disable EAE on SIMH, unfortunately.

What you're getting means that the compiler, runtime, and libraries are 
not from the same release.
     -Rick