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From: rando@skipper.dfrf.nasa.gov (Randy Brumbaugh)
Newsgroups: comp.sys.transputer
Subject: 3L Compilers & Error Flag
Keywords: Error 3L C FORTRAN
Message-ID: <642@skipper.dfrf.nasa.gov>
Date: 18 Sep 90 18:56:22 GMT
Organization: NASA Ames-Dryden FRF, Edwards, CA
Lines: 35

The 3L C and 3L FORTRAN compiler manuals state that 
code generated by these compilers may cause the error
flag to be set, in the interest of efficiency.  This
has led to some discussion around here, and we have several
questions we can't answer.  Anybody else know anything
about this?

1)  Why do they need to set the error flag?  I don't
 understand how this improves efficiency.  Furthermore,
 when I look in the Transputer Reference Manual and
 see the instructions which cause this flag to be set
 (divide by zero, overflow, out-of-bounds, etc), I
 wonder - aren't these errors things that shouldn't
 happen.  Aren't they things that should cause an
 error?

2)  What conditions cause this to be set?
 Is it certain operations, or a sequence, or a complex
 data structure reference or what?

3)  Is there any way to program and be sure that the
 error flag won't be set by normal operation, so that 
 it may be used for debugging?

4)  How are other people debugging complex, multi-xputer
 systems, without using the Error siganl?  It seems
 like the Error signal is about the only way to detect
 software faults easily and simply.

Any answers, comments, or suggestions are appreciated.
Post or e-mail

Thanks,
  Randy Brumbaugh
  rando@skipper.dfrf.nasa.gov