[LUCENE-3449] Fix FixedBitSet.nextSetBit/prevSetBit to support the common usage pattern in every programming book

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 3.4, 4.0-ALPHA
• Component/s: core/other
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Uwe Schindler
• Created: 22/Sep/11 13:39
• Updated: 28/Aug/22 12:57

Description

The usage pattern for nextSetBit/prevSetBit is the following:

for(int i=bs.nextSetBit(0); i>=0; i=bs.nextSetBit(i+1)) {
 // operate on index i here
}

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:

for(int i=bs.nextSetBit(0); i>=0; i=(i<bs.length()-1) ? bs.nextSetBit(i+1) : -1) {
 // operate on index i here
}

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.

Issue Links

• relates to: LUCENE-3448 Add FixedBitSet.and(other/DISI), andNot(other/DISI)