On Sat, 15 Aug 2020, Damian McGuckin wrote:
> I have a little loop which is either 1, 2 or 4 iterations long.
>
> I want it unrolled by the compiler so its index should be a param.
>
> Its upper and lower limits are all param which are 0 and #size.
>
> param block = 0 .. #size
I think the first problem is that the compiler isn't complaining about
this line. The language spec's section on params says that params are
limited to primitive and enumerated types, which I don't believe includes
ranges.
If I change the "for param b in block" to
"for param b in 0..#size", the compiler doesn't complain about that line.
> where size is a param itself.
>
> Chapel complains in its 3 usages below, namely
>
> [param b in block]
This construct is equivalent to a forall expression, and there's no such
thing as a param forall expression.
> var x = [param b in block] u[r + b, j];
Unfortunately, there's also no param for expression, just a param for
statement. So I don't think you can get this loop unrolled and used for
initialization. Though you could use split initialization to hand-unroll
it for the legal values of size.
Alternately,
var x = [b in block] u[r + b, j];
Lastly,
> [param b in block] u[r + b, k] = x[s];
This one can be an unrolled param for statement, or a forall loop; not
both.
If I change it to a "for param b in 0..#size" style loop in addition to
the above changes, the only thing the compiler complains about is that s
is out of scope there.
Paul
> and
> for b in block
>
> What am I doing wrong?
>
> Yes, I can manually unroll the loop myself and have three instances of the
> routine but that is messy.
>
> The usage is below.
>
> inline proc vmRot(jk : range, r : int, param size : int, q : [] ?C, u : [] ?R)
> {
> const (j, k) = (jk.first, jk.last);
> param block = 0..#size;
> var x = [param b in block] u[r + b, j];
>
> for i in j+1 .. k do
> {
> const gi = g[i];
> const c = gi.re;
> const s = -gi.im;
>
> for param b in block do
> {
> const yi = u[r + b, i];
> const xi = x[b];
> const cxi = c * xi;
> const cyi = c * yi;
>
> u[r + s, i - 1] = cxi - s * yi;
> x[s] = cyi + s * xi;
> }
> }
>
> [param b in block] u[r + b, k] = x[s];
> }
>
> Thanks - Damian
>
> Pacific Engineering Systems International, 277-279 Broadway, Glebe NSW 2037
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