[Simh] PDP-7 DECsys bug

[bsupnik at comcast.net]

The PDP-7 doesn't have floating point hardware.  It does have hardware multiply/divide (extended arithmetic element or EAE), and that has been tested with diagnostics.  IIRC, PDP-7 floating point is done with an interpreter, which makes it quite difficult to trace code flow without sources.

I agree with Dave Bryan that fault isolation is key: is the bug in the format routine, or earlier?  I was hoping that EQUIVALENCE would let the 3-word floating point variable AA be printed as integers, but that's not supported.  Some possible experiments:

1. Try E formating instead of F formating.
2. Try 2WORD representation instead of 3WORD.
3. Dump the assembler output from the compiler (A,filename in DECsys rather than F,filename) to see if there's a 'hook' for putting breakpoints in the program.
4. Use the write binary capability to write AA to a binary DECtape and dump the result. (It doesn't appear that binary output is supported to the paper tape punch, although you could try it.)

/Bob