>I finished reading the code for the routine "count" in the C source for
>the Go playing program Wally. I downloaded it a long time ago but it
should
>be at
>http://www.usgo.org/resources/computer.html
>I know there are better programs but I'm just doing this for practice and
this
>is a fairly small program to study. The routine takes as inputs the
integer
>coordinates of a position on the board and also some parameters, one of
which
>is a board (i.e. double array of int of a certain size), called
"scratch",
>which is used to keep track of which positions have been looked at. After
>modifying the entry of scratch for the position (x,y), it then examines
the
>(up to) 4 adjacent positions and, in each case, if certain conditions are
met,
>it runs through the code for that position. Let me be more precise about
that:
>for the first 3 of the 4 possible adjacent positions, it runs through the
code
>by calling "count" with the same parameters except at this adjacent
position,
>but for the 4th it jumps to a label at the beginning of the code for
"count".
>
>So, in all 4 cases, it seems that the behavior is essentially the same.
Where does it go to *after* it has completed the calculation? The
behavior is *not* essentially the same. You can convert the *last*
recursive call of the form:
return foo(some args);
into assigning the value of those args and goto the beginning of the
function. The same is not true of recursive calls that aren't last.
In order to make the function entirely non-recursive, you'd need
to introduce a stack of positions to keep track of. This was not
done possibly because it was viewed as (a) too complicated to bother
coding, (b) too inefficient, or (c) too difficult to maintain.
>What I'd like to know is whether there is any reason why it might be
>advantageous to use a goto in the 4th case but a self-call in the other
>three cases? Would it be better to use the goto in all 4 cases, e.g. due
>to some overhead from the function call?
If it doesn't have to work correctly, any algorithm can be done in
zero CPU time and zero bytes.
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