[viff-devel] Vedr.: Small VIFF language parser

[Martin Geisler]

Janus Dam Nielsen <fagidiot at daimi.au.dk> writes:

> Hi again,
>
> Heres the fruit of half a days work :)
>
> Analyzing the expression:
>     sint n = (a * y + (1 - a) * x);
>
> Yields the following results:
>
> Final result:
> ((a * y )+ ((1 - a )* x )) cost: 30
> (((a * y )+ x )- (x * a )) cost: 30
> (((a * y )+ x )- (a * x )) cost: 30
> (((a * y )- (a * x ))+ x ) cost: 30
> (((y * a )+ x )- (a * x )) cost: 30
> (((y * a )+ x )- (x * a )) cost: 30
> ((a * y )+ (x - (x * a ))) cost: 30
> (((y * a )- (a * x ))+ x ) cost: 30
> (((y * a )- (x * a ))+ x ) cost: 30
> (((a * y )- (x * a ))+ x ) cost: 30
> ((a * (y - x ))+ x ) cost: 20
>
> And lo and behold the last line reveals that the expression
> a * (y - x )+ x
> has the lowest cost.

That is very cool! :-)

>From the output above it seems that you have taught your analyzer
about the distributive law, that + and * are commutative.

What about a - a == 0, and that 0 * a == 0? I don't know if those
rules will help -- they might just blow up the search space... :-)

-- 
Martin Geisler