[Info-vax] Looking for suggestions for new $GETDVI item codes

[Bob Gezelter]

On Thursday, January 15, 2015 at 11:53:16 AM UTC-5, cme... at gmail.com wrote:
> On Thursday, January 15, 2015 at 9:23:55 AM UTC-5, Bob Gezelter wrote:
> 
> ...
> I very much disagree with that approach.  If VMS tells me something is FFFFFFFF blocks, I want to be able to believe it.
> 
My point is that 0x7FFFFFFF is the largest unsigned number in the field (0xFFFFFFFF if all code is verified to use the number unsigned). VMS would then be guaranteeing that AT LEAST that amount is available. 

You can believe it in the context that it is true, albeit potentially incomplete. For many programs, particularly those that are binary images using the existing API, that is likely enough.

In any event, maxing the field is a safer bet than truncating the result. Maxing returns 0x7FFF FFFF in a longword. Truncating 0x80 0000 0000 yields 0x0, which is far more damaging.

Maxing is not a cure-all, it is merely a more constructive response to back compatibility.

- Bob Gezelter, http://www.rlgsc.com