🚀 go-pugleaf

In article <8496@reed.UUCP> douglas@reed.UUCP (P Douglas Reeder) writes:
>I like being able to make the lower bound of an array  whichever I prefer
>and is the sensible one.  Allowing this requires only a trivial addition to
>array element evaluation:  the lower bound is subtracted from the index first.

That's way too complicated.  The right way is to bias the base address
of the array so that (Rn, Dn*ElementSize) points to the first element of the 
array when Dn's value is the lower index bound.   

Thus for 'a: ARRAY [m..n] OF Element', the compiler's (linker's)
internal base address for the array 'a' would be 

  ADR(firstElement) - (m * TSIZE(Element))

so that for positive m the base address is less than the address of the
first element by m * TSIZE(Element) size units, and for negative m it
is greater than the address of the first element by that amount.

This is just removing an invariant computation from run-time to compile-time
where it belongs.

--alann@pdn