tai/research/fuzzy-matching-selectors/github-fzy-match-c.md

fzy src/match.c

Metadata

Field	Value
Institute	Molodetz Institute — Research & Retrieval Division
Subject	fuzzy-matching-selectors
Document type	Source Dossier
Tier	1
Source title	fzy src/match.c
Source URL	https://raw.githubusercontent.com/jhawthorn/fzy/master/src/match.c
Source publisher / author	jhawthorn (fzy maintainer)
Source type	repository
Source date (published)	Unknown — not stated
Date researched	2026-10-25
Researched by	tai (agent), model: Claude Sonnet 5, on behalf of retoor
Research method	direct page fetch
Confidence	Medium
Status	Active

Summary

The C implementation of fzy's matcher. The scoring constants are not in this file (they live in config.h and bonus.h, which were not fetched), but the dynamic-programming recurrences, the prefilter and the length cap logic are.

Key findings

• has_match is a prefilter: for each needle byte it finds the next case-insensitive occurrence in the haystack and advances; it returns 0 when any byte is missing.
• match() and match_positions() return SCORE_MIN when the haystack is longer than MATCH_MAX_LEN or the needle is longer than the haystack.
• precompute_bonus starts with last_ch = '/' and sets match_bonus[i] = COMPUTE_BONUS(last_ch, ch): the bonus depends on the preceding character.
• Row recurrence: gap_score is SCORE_GAP_TRAILING on the last needle row, else SCORE_GAP_INNER. When needle[i] equals haystack[j]: for i == 0, score = j * SCORE_GAP_LEADING + match_bonus[j]; for i > 0 and j > 0, score = max(prev_M + match_bonus[j], prev_D + SCORE_MATCH_CONSECUTIVE). D[j] = score and M[j] = max(score, M[j-1] + gap_score). Otherwise D[j] = SCORE_MIN and M[j] = M[j-1] + gap_score.
• match() returns SCORE_MAX when needle and haystack have the same length; otherwise the last cell of M.

Pros / strengths

Exact, short, readable recurrences; shows the cheap prefilter that makes large candidate lists affordable.

Cons / limitations / caveats

Constants (SCORE_GAP_, SCORE_MATCH_) and MATCH_MAX_LEN are not defined in the fetched file, so no numbers can be quoted from it.

Relevance to tai

The recurrence is the shape of FuzzyMatcher::Subsequence (D = ends in match, M = best prefix). The prefilter idea is covered by the n > m early return.

Changelog

Date	Change
2026-10-25	Initial dossier created.