On Mon, 2009-02-16 at 14:33 -0800, Xiaobin Lu wrote: > Webrev: http://webrev.invokedynamic.info/xiaobin.lu/6622432/ > > 6622432: RFE: Performance improvements to java.math.BigDecimal
<snip> > As you know, the division operation is expensive and the > algorithm to compare with the ten's power array can be made more > efficiently by correlating the bit length of the number with the index > to the array so that the time to compute the precision is O(1) rather > than being O(n) (where n is the length of the array). And that is > exactly what we are doing in the webrev. First, we get the bit length of > the number and then multiply it with log2 (10 base), use the result to > index to a dynamically expanded ten's power array so that division > operation can be avoided completely. Actually I'm not reviewing the webrev but I have some questions. 1. Is bitCount() called often and performance critical? There is a RFE (6378821) to intrinsify it and I am thinking about to implement it. 2. Why is BigInteger using it's own implementation of bit-count (bitCnt()) instead of using Integer.bitCount()? -- Christian
