Bad-character rule — where it appears
Named by 5 essays across 2 fields — each of them below, with the objects they name alongside it.
The text that answers without reading it
Boyer–Moore–Horspool finds every occurrence of an eight-character pattern in a twenty-thousand-character text while examining 2,985 characters. Not 2,985 comparisons of eight characters each — 2,985 characters, 0.149 per character of text. It is a correct algorithm returning a complete answer about a text it has mostly not looked at, and the reason it can is a property of the alphabet rather than of the algorithm.
The shift somebody published
The exact rules for shifting a multi-pattern window are a definition that quantifies over every pattern at every offset. The 1979 rules are two tables read off the trie's own failure links, they are computed in one pass, and on this pattern set they agree with the definition at every node.
The table the links already knew
The exact good-suffix rule costs 757,058 character comparisons to build from its definition at 128 patterns, and 3,824 from the trie's failure links. Same table, checked at every node — a factor of 198, and the definition was never the algorithm.
What the approximation gives up
Compared at every one of the 3,736 decisions a search could ask about, the published shift rules and the exact ones agree at all of them on a set of 128 patterns. At two patterns they differ at five of 84, by up to four positions — and the run reads 6.3% more characters.
The ratio that was an implementation
This collection published a factor of forty-two between two shift rules' preprocessing. Sixty-nine per cent of the denominator was a table the published rule never reads, and the numerator was a definition rather than a construction. The corrected ratio is 1.6.
Named alongside it
The objects these essays reach for when they reach for this one.
Commentz-walterGood-suffix ruleMeasurementPreprocessingShift ruleFailure linkMulti patternPattern matchingTrieAho-corasickAlphabet sizeConstruction