[Info-vax] Dave Cutler, Prism, DEC, Microsoft, etc.

[Bob Koehler]

In article <msidnUqwec8o5ojWnZ2dnUVZ_g2dnZ2d at earthlink.com>, "John Reagan" <johnrreagan at earthlink.net> writes:
> 
> VAX Pascal also executes "useless" instructions (tstb #literal) at various 
> places as flags to the RTL.  The main one is getting UNSIGNED arithmetic not 
> to fault eventhough you want integer overflow enabled.  Since there is only 
> one ADDL instruction, we followed unsigned adds with a tstb #literal.  The 
> RTL's handler sees that special instruction, looks up the literal to see 
> what to do, and then bumps the PC and continues.  In cases where the ADD 
> didn't overflow, you execute the tstb #literal anyway.

   Interesting workaround.  I always thought IV should be allowed in 
   BICPSW/BISPSW.