Fix FixedBitSet.nextSetBit/prevSetBit to support the common usage pattern in
every programming book
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Key: LUCENE-3449
URL: https://issues.apache.org/jira/browse/LUCENE-3449
Project: Lucene - Java
Issue Type: Improvement
Components: core/other
Affects Versions: 3.4, 4.0
Reporter: Uwe Schindler
Priority: Minor
The usage pattern for nextSetBit/prevSetBit is the following:
{code:java}
for(int i=bs.nextSetBit(0); i>=0; i=bs.nextSetBit(i+1)) {
// operate on index i here
}
{code}
The problem is that the i+1 at the end can be bs.length(), but the code in
nextSetBit does not allow this (same applies to prevSetBit(0)). The above usage
pattern is in every programming book, so it should really be supported. The
check has to be done in all cases (with the current impl in the calling code).
If the check is done inside xxxSetBit() it can also be optimized to be only
called seldom and not all the time, like in the ugly looking replacement, thats
currently needed:
{code:java}
for(int i=bs.nextSetBit(0); i>=0; i=(i<bs.length()-1) ? bs.nextSetBit(i+1) :
-1) {
// operate on index i here
}
{code}
We should change this and allow out-of bounds indexes for those two methods
(they already do some checks in that direction). Enforcing this with an assert
is unuseable on the client side.
The test code for FixedBitSet also uses this, horrible. Please support the
common usage pattern for BitSets.
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