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Logarithm Algorithm

I need to evaluate a logarithm of any base, it does not matter, to some precision. Is there an algorithm for this? I program in Java, so I'm fine with Java code.

How to find a binary logarithm very fast? (O(1) at best) might be able to answer my question, but I don't understand it. Can it be clarified?

Solution

  • Use this identity:

    logb(n) = loge(n) / loge(b)

    Where log can be a logarithm function in any base, n is the number and b is the base. For example, in Java this will find the base-2 logarithm of 256:

    Math.log(256) / Math.log(2)
=> 8.0

    Math.log() uses base e, by the way. And there's also Math.log10(), which uses base 10.