Math parsing function/component anyone?

I'm looking for a reasonably light-weight, simple and fast math function parser. It should not be a DLL. I need it to work on Windows, MacOSX and iOS. I would use it in a demo I want to build.

It must be able to parse and evaluate functions of (at least) two variables, for instance f(x,y) = sin(x^2+y^2)/(x^2+y^2).

I would use it like this (pseudo code):

FuncTree := BuildEvalTree('f(x,y) = sin(x^2+y^2)/(x^2+y^2)'); // Or whatever it needs
for x := x_min to x_max do
  for y := y_min to y_max do
    z[x,y] := Evaluate(FuncTree,[x,y]); // Or whatever it needs...

Thanks!