This week's book giveaway is in the Servlets forum. We're giving away four copies of Murach's Java Servlets and JSP and have Joel Murach on-line! See this thread for details.

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.

Using an "(int)" cast to create an integer from a floating point number is rather crude, especially since floating point arithmetic on computers is fundamentally imprecise (see #20 here to understand why). Depending on your circumstances, Math.round, Math.ceil or Math.floor may be a better way to do that.