logarithms : Java Glossary

Java’s Math.log computes natural logarithms (base e=2.718281828…) usually written by engineers as ln. To get base ten common logs, calculate Math.log(x)/Math.log(10). To get base 2 logs, calculate Math.log(x)/Math.log(2). In Java version 1.5 or later there is a built-in Math. log10.

What you often want is the width in bits, or width in digits.


For computing natural logs of values near 1, there is Math. log1p(x+1). To get the log of 1.00000000789d you call log1p( 0.00000000789d ). The constant 0.00000000789d is more precise than 1.00000000789d.

Sun’s notation is confusing: Does log1p( x+1 ) mean you are supposed to pass x + 1 as the parameter to get log x, or does it mean you pass x as the parameter to get the log of x+1? It is the second.

Example Use

Learning More

Oracle’s Javadoc on log package : available:
Oracle’s Javadoc on log10 package : available:
Oracle’s Javadoc on log1p package : available:
Oracle’s Javadoc on exp package : available:
Oracle’s Javadoc on expm1 package : available:

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