19 lines
819 B
Elixir
19 lines
819 B
Elixir
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# You can ignore this file if you're solving this exercise in the web editor,
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# or on your own computer if you have Elixir version 1.12 or higher.
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# You can check which Elixir version you have by running `elixir -v` in your terminal.
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defmodule Math do
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import Bitwise
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# copied from https://github.com/elixir-lang/elixir/blob/v1.12.0/lib/elixir/lib/integer.ex#L103-L114
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def pow(base, exponent) when is_integer(base) and is_integer(exponent) do
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if exponent < 0, do: raise("exponent cannot be negative")
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guarded_pow(base, exponent)
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end
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# https://en.wikipedia.org/wiki/Exponentiation_by_squaring
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defp guarded_pow(_, 0), do: 1
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defp guarded_pow(b, 1), do: b
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defp guarded_pow(b, e) when (e &&& 1) == 0, do: guarded_pow(b * b, e >>> 1)
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defp guarded_pow(b, e), do: b * guarded_pow(b * b, e >>> 1)
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end
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