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erlangelixir

Elixir floating point division accuracy

I'm observing some unexpected floating point behaviour in Elixir.

4.7 / 0.1 = 47.0 (good!)
4.8 / 0.1 = 47.9999999999 (bad!)
4.9 / 0.1 = 49 (good!)

While I understand the limitations of fp accuracy, in this case, the answer just looks wrong.

Curiously, I tried this in python as well, and got the same result, which is even more mysterious. When I changed the format to 4.8 * (1/0.1), I get the right answer (48.0).

What is going on here?

Solution

  • This is actually a normal behavior for IEEE 754 floating point numbers, and unrelated to erlang/elixir. Python or Nodejs would return the same thing.

    For more information, you can read this detailed explanation.