question about copyright and code, is this legal?

[Jonathan Wilson]

Say I have a piece of code, x (which is copyright) which always returns the 
same output for a given input (e.g. a function that implements a math 
formula or a function that retrieves some value from an internal data table 
stored in the dll or whatever)
Lets then say that I havent seen this code (either origonal C code or 
disassembly)
Say I was to write a program that calls this function for all valid inputs 
and prints the inputs and outputs.
If I was to take the output of this program and, without refering to the 
origonal function or the dump program in any way (i.e. using just the 
"truth table" for the function) generate a function that, for any given 
input, generates the same output as the original, have I broken the law?