On Mon, 20 Apr 2015 13:09:14 +0800, Timothy Sipples wrote: >Clark Morris wrote: >>Given that IBM CSP and its descendants (IBM VisualAge generator) >>generate F signs for positive fields.... > >My understanding is that the currently supported descendants, i.e. EGL, >don't behave this way. > I'm a skeptic about Postel's Principle. Rather, I believe that hardware or software as appropriate should enforce preferred values for otherwise uncommited fields in instructions, data, and control blocks lest overly inventive programmers exploit them to smuggle a few bits of data through whatever interface. I'll even go so far as to say that if the original s/360 had raised an addressing excption when bits 0-7 of a base or index register were nonzero, transition from 24-bit to 32-bit addressing would have been much facilitated.
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