OpenEuphoria

Re: and...and...and

• Posted by Ralf Nieuwenhuijsen <nieuwen at XS4ALL.NL> Jan 01, 1970
• 2618 views

Robert Craig wrote:

> > -the last one is the fastest. Shouldn't Euphoria just skip the rest
> of an
> "if
> > ... and" line if the first part checks false? It seems to me that
> all parts
> of
> > an "if ... and ... and" line is checked each time, which did result
> in a
> > slowdown in my game.
>
> You are correct. Euphoria does not do "short-circuit" evaluation of
> and/or/not
> conditions.
> I have this on my list of desirable features, but it might not happen
> for a
> while,
> if at all, because:
>
>    1. It's hard to retrofit this in to ex.exe.

    Can't you put it in the precompiler as different if's

>    2. It would break some people's existing code (only a tiny
> percentage I
> would guess)
>        in the case where there are side effects from evaluation (e.g.
> function
> call sets a global variable)

    The precompiler makes a first if with only those evulations that
have a side effect. (That call another function or routine). After that
it can compile the rest of the evalutions on different (sub)-ifs

>    3. Euphoria's conditional expressions can involve sequences, as
> well as
> atoms. e.g.
>       if A and B then ..., where A is 1 and B is {0,1,2} is supposed
> to
> evaluate to {0,1,1}
>       which is supposed to cause an error when used in an if
> statement. We'd
> have to
>       accept A and B as being "true" without any error message.

    Have the objects also in the first if.

> > Do the rest of you know of other "trivial things" which could have a
>
> > major impact on speed?
>
> In Euphoria there are a surprising number (even to me)
> of trivial things that can affect performance. This is generally due
> to the
> fact that Euphoria does not map directly to machine code the way C
> does.
> The Euphoria interpreter is doing "invisible" things, such as storage
> allocation,
> in order to give you a simple, safe, flexible world to program in.

       I'll give you two examples that will show a weird speed
difference...

-- Example 1
    function my_func (sequence r)
    sequence s
        s = r[1][2][3][4]
        if s[1] = 1 then
        elsif s[2] = 2 then
        elsif s[3] = 3 then
        elsif s[4] = 4 then
        elsif s[5] = 5 then
        elsif s[6] = 6 then
        end if
        my_procedure (s+4+s)
        return s+ (s*2)
    end function

-- Example 2
    function my_func (sequence r)
        if r[1][2][3][4][1] = 1 then
        elsif r[1][2][3][4][2] = 2 then
        elsif r[1][2][3][4][3] = 3 then
        elsif r[1][2][3][4][4] = 4 then
        elsif r[1][2][3][4][5] = 5 then
        elsif r[1][2][3][4][6] = 6 then
        end if
        my_procedure (r[1][2][3][4]+4+r[1][2][3][4])
        return r[1][2][3][4]+ (r[1][2][3][4]*2)
    end function

-- End of examples

 The first code looks nicer, but declares a sequence and copy
r[1][2][3][4] to it.
            and that code is still faster (on my machine: p60, 24 mb,
win95)
I think it is because every time you use r[1][2][3][4], it looks up r[1]
then r[1][2] then r[1][2][3] then r[1][2][3][4]. (It will be passed
forwared 3 times)
However the other code doens't actually copy it. It only copies the
link/ the pointer to the sequence of r[1][2][3][4]. And when we change a
value in it, Then it will start copying the whole sequence. (But we
don't)

Ralf Nieuwenhuijsen
nieuwen at xs4all.nl