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Math.log problem in JDK1.4

Suganthi Velliah

Joined: Apr 30, 2007
Posts: 17
Hi All,

While calculating logarithm values in JDK1.4 it returns some unpredicted values. As Math.log() returns double so there is loss of precision and exact log base 10 values cannot be calculated.

For a CR in TP, a formula was given as:

DispCode = Int ( -1 * log10( abs(LsbRsln)))

which is written in Java as,

int dispcode = (int) (-1 * (Math.log(Math.abs(Double.parseDouble(lsbrsln))) / Math.log(10)));

For example, if lsbrsln = 0.001, the formula is expected to return 3, instead it returns 2. The following part of the formula

Math.log (Math.abs (Double.parseDouble(0.001))) / Math.log(10) is returning -2.999999� and finally the formula is returning 2 while casting it into int.

In JDK1.5 we have Math.log10 method itself for calculating logbase10 values. But since we need to support JDK1.4 also we were not able to use that also.

Please let me know if you have the solution.
Ulf Dittmer

Joined: Mar 22, 2005
Posts: 42364
Please do not post the same question multiple times. Let's continue the discussion in this duplicate thread, where you have an answer already.

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It is sorta covered in the JavaRanch Style Guide.
subject: Math.log problem in JDK1.4