Fix wavelet tree get_segment crash for alphabet_size=1#60
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Fix wavelet tree get_segment crash for alphabet_size=1#60kilo-code-bot[bot] wants to merge 1 commit into
kilo-code-bot[bot] wants to merge 1 commit into
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When alphabet_size == 1, the wavelet tree has no internal nodes (root_ == npos). The get_segment_impl method unconditionally called copy_segment_content(root_, ...) which accessed nodes_[npos], causing an out-of-bounds access since nodes_ is empty. rank_impl and select_impl already handled root_ == npos correctly (the traversal loop simply does not execute), but get_segment_impl had no guard for this degenerate case. Fix: add an early return in get_segment_impl when root_ == npos. In this case all symbols are identical, so the result is the single symbol (inverse_permutation_.front()) repeated (end - begin) times. Also add edge-case test coverage: - AlphabetSizeOne: rank, select, and get_segment for single-symbol alphabets (both Standard and Huffman builds) - AlphabetSizeZero: empty alphabet edge case - EmptyData: non-empty alphabet with no data - SymbolWithZeroOccurrences: symbols present in the alphabet but absent from the data - AllSameSymbolLargeAlphabet: one symbol repeated with a large alphabet where most symbols have zero occurrences
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #60 +/- ##
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+ Coverage 90.10% 90.21% +0.11%
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Files 39 39
Lines 8735 8783 +48
Branches 1418 1433 +15
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+ Hits 7871 7924 +53
+ Misses 447 443 -4
+ Partials 417 416 -1
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Owner
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This kind of things should probably be handled in constructor, the case of alphabet size 1 is indeed of no use |
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Summary
Fixes a crash in
WaveletTreeIndex::get_segment_implwhenalphabet_size == 1(or any case whereroot_ == nposwithdata_size_ > 0).Related to #41 (Wavelet tree implementation with general rank/select).
Bug
When
alphabet_size == 1, the wavelet tree has no internal nodes (root_ == npos). Theget_segment_implmethod unconditionally calledcopy_segment_content(root_, ...), which accessednodes_[npos]— an out-of-bounds index sincenodes_is empty.rank_implandselect_implalready handledroot_ == nposcorrectly (the traversal loop simply does not execute), butget_segment_implhad no guard for this degenerate case.Fix
Add an early return in
get_segment_implwhenroot_ == npos. In this case all symbols are identical, so the result isinverse_permutation_.front()repeated(end - begin)times.Test coverage additions
Files changed
include/pixie/wavelet_tree/index.h: 5-line fix inget_segment_implsrc/tests/wavelet_tree_tests.cpp: 4 new test cases covering edge cases