Integer arithmetic

Can you do signend arithmetic with integer type. I am negating it here
and seem to be getting strange results.

subtype POINTER is integer range 0 to 16383;
subtype BYTECOUNT is integer range 0 to 16383;

signal readpointer : POINTER;
signal writepointer : POINTER;
signal diffpointer : BYTECOUNT;

.....

if (writepointer >= readpointer) then
diffpointer <= writepointer - readpointer;
else
diffpointer <= (16383-readpointer)+writepointer;
end if;

nfirtaps

"nfirtaps" <> wrote in message
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> Can you do signend arithmetic with integer type. I am negating it here
> and seem to be getting strange results.
>
> subtype POINTER is integer range 0 to 16383;
> subtype BYTECOUNT is integer range 0 to 16383;
>
> signal readpointer : POINTER;
> signal writepointer : POINTER;
> signal diffpointer : BYTECOUNT;
>
> ....
>
> if (writepointer >= readpointer) then
> diffpointer <= writepointer - readpointer;
> else
> diffpointer <= (16383-readpointer)+writepointer;
> end if;
>

Try this...
subtype POINTER is integer range 0 to 16383;
subtype BYTECOUNT is integer range -16383 to 16383;

signal readpointer : POINTER;
signal writepointer : POINTER;
signal diffpointer : BYTECOUNT;
....
diffpointer <= writepointer - readpointer;

KJ