math expression evaluation - very fast - with objective-c

i want to evaluate a math expression like y = 2(x * x) + 2.

But i need it in a loop, where the x changes maybe 100000 times.

I have written code to translate the expression in a parse tree.

Then i have a method to evaluate the parse tree.

- (double) evaluate:(TreeNode *)node variable:(double)x
{
    if ([node _operand] != 0) 
    {
        return [node _operand];
    }

    else if ([node _variable] != NULL) 
    {
        return x;
    }

    else if ([node _operator] != NULL) 
    {
        if ([[node _operator] isEqualToString: @"+"]) 
        {
            return ([self evaluate:[node left] variable:x] + [self evaluate:[node right] variable:x]);
        }
        else if ([[node _operator] isEqualToString: @"-"]) 
        {
            return ([self evaluate:[node left] variable:x] - [self evaluate:[node right] variable:x]);
        }
        else if ([[node _operator] isEqualToString: @"*"]) 
        {
            return ([self evaluate:[node left] variable:x] * [self evaluate:[node right] variable:x]);
        }
        else if ([[node _operator] isEqualToString: @"/"]) 
        {
            return ([self evaluate:[node left] variable:x] / [self evaluate:[node right] variable:x]);
        }
    }

    return 0;
}

Someone said: if i gotta go for speed, i could translate the expression into C code, compile and link it into a dll on-the-fly and load it (takes about a second). That, plus memoized versions of the math functions, could give me the best performance.

How can i achive that ? How can i compile the math expression into C code and compile and link it into a dll or so. And then load it on the fly to speed the loop up ?

Thanks a lot !

Chris