[rhengles]

Forgive me for replying here, I couldn't find an option to DM you. And I cannot find any implementation of this in javascript, nor anyone else able to help me.

Can you shed some light here why I'm getting these differences?

https://jsfiddle.net/7kf15dje/

Here is an example of the output I'm getting:

  //       X  A  B           X^1         X^-1 :: Difference
   471490377  6 13 =  1365552781 =  471490377 :: 0
  1528396978  9 11 = -1576695076 = 1528396978 :: -0
  1592322722  9 20 =   622346385 = 1592322722 :: -0
  1214152986  8 16 = -1748578289 = 1214152985 :: -1
  1193897367  2 16 =   907713766 = 1193897366 :: -1
   335642564  9 10 =   318891964 =  335642564 :: -0
   486208953 16 23 =   894211128 =  486208952 :: -1
   629577059 13 14 =  1383225523 =  629577058 :: -1
  1609442937  8 18 =   674046110 = 1609442937 :: -0
   234450967  6 12 =  -459008694 =  234450966 :: -1
  1840721644 19 28 =  -602984005 = 1840721644 :: -0

[rhengles]

I can't edit my post anymore but I found the solution. All I had to do was to convert the random input value (X above) to an uint32 using (X >>> 0).

[dragontamer]

You did things the hard way by trying to construct the exact inverse.

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I suggest the following instead:

1. Create a 16-gigabyte file consisting of f(x) from x=0x00000000 to x=0xFFFFFFFF.

2. Sort the file.

3. Determine that no repeats exist, that is, the values go from 0x00000000 to 0xFFFFFFFF.

--------

Once you have determined that all 32-bit inputs result in all 32-bit outputs, you've determined that the function is invertible. 4-bytes x 2^32 possible inputs == only 16GB these days, small enough to be handled by any old computer... possibly entirely in RAM.

But if you don't got enough RAM for that, an SSD or even Hard Drive would be fast enough for the above procedure. It may take a few minutes but its not that hard.

You see, the goal is to "prove you have an invertible function". At no point do you have to accomplish the difficult task of actually finding the inverse.

-------

Well, I guess if you're "just following the blogpost" about the inverse, maybe that's easier. But from the perspective of "I don't know the inverse yet", its really difficult to figure it out. So you should think about the simpler brute-force methodologies that a modern computer can do in just a few minutes.