function to multiply very small or very big numbers

How can I multiply by a *10^(-20). I couldn't find any logarithmic functions so I hope开发者_JAVA技巧 there will be some others

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Java doubles cover the range 4.9*10^-324 to 1.7*10^308, positive or negative. If your numbers fit within that range, and you are happy to use floating point precision, you can use the normal * operator.

The documentation for the Math.log method is here.

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You can use BigDecimal class which can store large values for your calculations.

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I wouldn't use a log function, I would use Math.pow

 double d = a * Math.pow(10, -20);