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fts_fuzzy_match.hpp
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fts_fuzzy_match.hpp
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// LICENSE
//
// This software is dual-licensed to the public domain and under the following
// license: you are granted a perpetual, irrevocable license to copy, modify,
// publish, and distribute this file as you see fit.
//
// VERSION
// 0.2.0 (2017-02-18) Scored matches perform exhaustive search for best score
// 0.1.0 (2016-03-28) Initial release
//
// AUTHOR
// Forrest Smith
//
// NOTES
// Compiling
// You MUST add '#define FTS_FUZZY_MATCH_IMPLEMENTATION' before including this header in ONE source file to create implementation.
//
// fuzzy_match_simple(...)
// Returns true if each character in pattern is found sequentially within str
//
// fuzzy_match(...)
// Returns true if pattern is found AND calculates a score.
// Performs exhaustive search via recursion to find all possible matches and match with highest score.
// Scores values have no intrinsic meaning. Possible score range is not normalized and varies with pattern.
// Recursion is limited internally (default=10) to prevent degenerate cases (pattern="aaaaaa" str="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
// Uses uint8_t for match indices. Therefore patterns are limited to 256 characters.
// Score system should be tuned for YOUR use case. Words, sentences, file names, or method names all prefer different tuning.
#ifndef FTS_FUZZY_MATCH_H
#define FTS_FUZZY_MATCH_H
#include <ctype.h> // ::tolower, ::toupper
#include <cstdint> // uint8_t
#include <cstdio>
#include <cstring> // memcpy
#include <iostream>
// Public interface
namespace fts {
static bool fuzzy_match_simple(char const* pattern, char const* str);
static bool fuzzy_match(char const* pattern, char const* str, int& outScore);
static bool fuzzy_match(char const* pattern, char const* str, int& outScore, uint8_t* matches, int maxMatches);
} // namespace fts
#ifdef FTS_FUZZY_MATCH_IMPLEMENTATION
namespace fts {
// Forward declarations for "private" implementation
namespace fuzzy_internal {
static bool fuzzy_match_recursive(const char* pattern, const char* str, int& outScore, const char* strBegin,
uint8_t const* srcMatches, uint8_t* newMatches, int maxMatches, int nextMatch,
int& recursionCount, int recursionLimit);
}
// Public interface
static bool fuzzy_match_simple(char const* pattern, char const* str) {
while (*pattern != '\0' && *str != '\0') {
if (tolower(*pattern) == tolower(*str))
++pattern;
++str;
}
return *pattern == '\0' ? true : false;
}
static bool fuzzy_match(char const* pattern, char const* str, int& outScore) {
uint8_t matches[256];
return fuzzy_match(pattern, str, outScore, matches, sizeof(matches));
}
static bool fuzzy_match(char const* pattern, char const* str, int& outScore, uint8_t* matches, int maxMatches) {
int recursionCount = 0;
int recursionLimit = 10;
return fuzzy_internal::fuzzy_match_recursive(pattern, str, outScore, str, nullptr, matches, maxMatches, 0, recursionCount, recursionLimit);
}
// Private implementation
static bool fuzzy_internal::fuzzy_match_recursive(const char* pattern, const char* str, int& outScore,
const char* strBegin, uint8_t const* srcMatches, uint8_t* matches, int maxMatches,
int nextMatch, int& recursionCount, int recursionLimit) {
// Count recursions
++recursionCount;
if (recursionCount >= recursionLimit)
return false;
// Detect end of strings
if (*pattern == '\0' || *str == '\0')
return false;
// Recursion params
bool recursiveMatch = false;
uint8_t bestRecursiveMatches[256];
int bestRecursiveScore = 0;
// Loop through pattern and str looking for a match
bool first_match = true;
while (*pattern != '\0' && *str != '\0') {
// Found match. We assume a space in the pattern is match so we can match paths better
if (tolower(*pattern) == tolower(*str) || *pattern == ' ') {
// Supplied matches buffer was too short
if (nextMatch >= maxMatches) {
return false;
}
// "Copy-on-Write" srcMatches into matches
if (first_match && srcMatches) {
memcpy(matches, srcMatches, nextMatch);
first_match = false;
}
// Recursive call that "skips" this match
uint8_t recursiveMatches[256];
int recursiveScore;
if (fuzzy_match_recursive(pattern, str + 1, recursiveScore, strBegin, matches, recursiveMatches, sizeof(recursiveMatches), nextMatch, recursionCount, recursionLimit)) {
// Pick best recursive score
if (!recursiveMatch || recursiveScore > bestRecursiveScore) {
memcpy(bestRecursiveMatches, recursiveMatches, 256);
bestRecursiveScore = recursiveScore;
}
recursiveMatch = true;
}
// Advance
matches[nextMatch++] = (uint8_t)(str - strBegin);
++pattern;
}
++str;
}
// Determine if full pattern was matched
bool matched = *pattern == '\0' ? true : false;
// Calculate score
if (matched) {
const int sequential_bonus = 15; // bonus for adjacent matches
const int separator_bonus = 30; // bonus if match occurs after a separator
const int camel_bonus = 30; // bonus if match is uppercase and prev is lower
const int first_letter_bonus = 15; // bonus if the first letter is matched
const int leading_letter_penalty = -5; // penalty applied for every letter in str before the first match
const int max_leading_letter_penalty = -15; // maximum penalty for leading letters
const int unmatched_letter_penalty = -1; // penalty for every letter that doesn't matter
// Iterate str to end
while (*str != '\0')
++str;
// Initialize score
outScore = 100;
// Apply leading letter penalty
int penalty = leading_letter_penalty * matches[0];
if (penalty < max_leading_letter_penalty)
penalty = max_leading_letter_penalty;
outScore += penalty;
// Apply unmatched penalty
int unmatched = (int)(str - strBegin) - nextMatch;
outScore += unmatched_letter_penalty * unmatched;
// Apply ordering bonuses
for (int i = 0; i < nextMatch; ++i) {
uint8_t currIdx = matches[i];
if (i > 0) {
uint8_t prevIdx = matches[i - 1];
// Sequential
if (currIdx == (prevIdx + 1))
outScore += sequential_bonus;
}
// Check for bonuses based on neighbor character value
if (currIdx > 0) {
// Camel case
char neighbor = strBegin[currIdx - 1];
char curr = strBegin[currIdx];
if (::islower(neighbor) && ::isupper(curr))
outScore += camel_bonus;
// Separator
bool neighborSeparator = neighbor == '_' || neighbor == ' ' || neighbor == '/' || neighbor == '-';
if (neighborSeparator)
outScore += separator_bonus;
} else {
// First letter
outScore += first_letter_bonus;
}
}
}
// Return best result
if (recursiveMatch && (!matched || bestRecursiveScore > outScore)) {
// Recursive score is better than "this"
memcpy(matches, bestRecursiveMatches, maxMatches);
outScore = bestRecursiveScore;
return true;
} else if (matched) {
// "this" score is better than recursive
return true;
} else {
// no match
return false;
}
}
} // namespace fts
#endif // FTS_FUZZY_MATCH_IMPLEMENTATION
#endif // FTS_FUZZY_MATCH_H

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