review request for 6622432
Christian.Thalinger at Sun.COM
Tue Feb 17 11:15:15 UTC 2009
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
> 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()?
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