wc.in

idel虚拟机源码

: u/     [-0+0] u/mod [-2+2] { quot rem } [-2+0] quot [-2+1] ;
: /mod   [-1+0] u/mod [-2+2] { quot rem } [-2+0] rem [-2+1] ;

Stack effect for u. is (pop n, push n+d)

: u. [-0+0] { u } [-1+0]
  9 [-1+1] u [-1+2] u< [-1+1] if
    [-1+0] u [-1+1] 10 [-1+2] u/ [-1+1] u. [-x+y]  then
  [where x = max(1, n-1) and y = 1+d]
  [-1+0] [x=1,y=0]
  etc... ;


[-x+y] followed by (pop n, push n+d) is: [-max(x,n-y)+(y+d)]

so n = constant
     | max(n,n-y)
   d = constant
     | y+d

Let's represent everything as stack deltas, instead:

[md,d] [me,e] -> [min(md,d+me), d+e]

delta ::= constant
       |  variable
       |  delta+delta
       |  min(delta, delta)

equation ::= (delta = delta)

We construct equations at two places: function entries and conditional
joins.  We want to compute a least fixed point of a system of
equations.  It doesn't necessarily exist.

Also if we allow separate compilation we'll need stack-effect
declarations anyway.  So we might as well just add them in now, and
use them.