Re: is Vax addressing sane today

On 2024-09-21 4:51, MitchAlsup1 wrote:

On Sat, 21 Sep 2024 1:12:11 +0000, Lawrence D'Oliveiro wrote:
 

On Fri, 20 Sep 2024 18:35:26 -0000 (UTC), Kent Dickey wrote:
>

3) You want to clamp the value to a reasonable range and continue.  The
    reasonable values need to be looked up somewhere.

>
This won’t work. The values outside the range are by definition non-
representable, so comparisons against them are useless.

 When a range is 0..10 both -1 and 11 are representable in
the arithmetic of ALL computers, just not in the language
specifying the range.

For "11" I agree, for "-1" disagree.
if the program was written (in whatever language) with the assumption that the data type in question is unsigned, then it cannot represent -1 in the program's view of the bits. The bits that represent -1 in a signed two's complement view represent a large positive value in the unsigned view that the code uses.
Now if the error condition that was trapped or detected was an attempt to produce a negative value like -1 for an unsigned data type, that error condition is of course representable separately; it does not have to be encoded by an out-of-range value in the data type itself.