1/* Functions to make fuzzy comparisons between strings 2 Copyright (C) 1988-1989, 1992-1993, 1995, 2001-2003, 2006 Free Software Foundation, Inc. 3 4 This program is free software: you can redistribute it and/or modify 5 it under the terms of the GNU General Public License as published by 6 the Free Software Foundation; either version 3 of the License, or 7 (at your option) any later version. 8 9 This program is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU General Public License for more details. 13 14 You should have received a copy of the GNU General Public License 15 along with this program. If not, see <http://www.gnu.org/licenses/>. 16 17 18 Derived from GNU diff 2.7, analyze.c et al. 19 20 The basic idea is to consider two vectors as similar if, when 21 transforming the first vector into the second vector through a 22 sequence of edits (inserts and deletes of one element each), 23 this sequence is short - or equivalently, if the ordered list 24 of elements that are untouched by these edits is long. For a 25 good introduction to the subject, read about the "Levenshtein 26 distance" in Wikipedia. 27 28 The basic algorithm is described in: 29 "An O(ND) Difference Algorithm and its Variations", Eugene Myers, 30 Algorithmica Vol. 1 No. 2, 1986, pp. 251-266; 31 see especially section 4.2, which describes the variation used below. 32 33 The basic algorithm was independently discovered as described in: 34 "Algorithms for Approximate String Matching", E. Ukkonen, 35 Information and Control Vol. 64, 1985, pp. 100-118. 36 37 Unless the 'find_minimal' flag is set, this code uses the TOO_EXPENSIVE 38 heuristic, by Paul Eggert, to limit the cost to O(N**1.5 log N) 39 at the price of producing suboptimal output for large inputs with 40 many differences. */ 41 42#include <config.h> 43 44/* Specification. */ 45#include "fstrcmp.h" 46 47#include <string.h> 48#include <stdbool.h> 49#include <stdio.h> 50#include <stdlib.h> 51#include <limits.h> 52 53#include "lock.h" 54#include "tls.h" 55#include "minmax.h" 56#include "xalloc.h" 57 58#ifndef uintptr_t 59# define uintptr_t unsigned long 60#endif 61 62 63#define ELEMENT char 64#define EQUAL(x,y) ((x) == (y)) 65#define OFFSET int 66#define EXTRA_CONTEXT_FIELDS \ 67 /* The number of elements inserted or deleted. */ \ 68 int xvec_edit_count; \ 69 int yvec_edit_count; 70#define NOTE_DELETE(ctxt, xoff) ctxt->xvec_edit_count++ 71#define NOTE_INSERT(ctxt, yoff) ctxt->yvec_edit_count++ 72/* We don't need USE_HEURISTIC, since it is unlikely in typical uses of 73 fstrcmp(). */ 74#include "diffseq.h" 75 76 77/* Because fstrcmp is typically called multiple times, attempt to minimize 78 the number of memory allocations performed. Thus, let a call reuse the 79 memory already allocated by the previous call, if it is sufficient. 80 To make it multithread-safe, without need for a lock that protects the 81 already allocated memory, store the allocated memory per thread. Free 82 it only when the thread exits. */ 83 84static gl_tls_key_t buffer_key; /* TLS key for a 'int *' */ 85static gl_tls_key_t bufmax_key; /* TLS key for a 'size_t' */ 86 87static void 88keys_init (void) 89{ 90 gl_tls_key_init (buffer_key, free); 91 gl_tls_key_init (bufmax_key, NULL); 92 /* The per-thread initial values are NULL and 0, respectively. */ 93} 94 95/* Ensure that keys_init is called once only. */ 96gl_once_define(static, keys_init_once) 97 98 99/* NAME 100 fstrcmp - fuzzy string compare 101 102 SYNOPSIS 103 double fstrcmp(const char *, const char *); 104 105 DESCRIPTION 106 The fstrcmp function may be used to compare two string for 107 similarity. It is very useful in reducing "cascade" or 108 "secondary" errors in compilers or other situations where 109 symbol tables occur. 110 111 RETURNS 112 double; 0 if the strings are entirly dissimilar, 1 if the 113 strings are identical, and a number in between if they are 114 similar. */ 115 116double 117fstrcmp (const char *string1, const char *string2) 118{ 119 struct context ctxt; 120 int xvec_length; 121 int yvec_length; 122 int i; 123 124 size_t fdiag_len; 125 int *buffer; 126 size_t bufmax; 127 128 /* set the info for each string. */ 129 ctxt.xvec = string1; 130 xvec_length = strlen (string1); 131 ctxt.yvec = string2; 132 yvec_length = strlen (string2); 133 134 /* short-circuit obvious comparisons */ 135 if (xvec_length == 0 && yvec_length == 0) 136 return 1.0; 137 if (xvec_length == 0 || yvec_length == 0) 138 return 0.0; 139 140 /* Set TOO_EXPENSIVE to be approximate square root of input size, 141 bounded below by 256. */ 142 ctxt.too_expensive = 1; 143 for (i = xvec_length + yvec_length; 144 i != 0; 145 i >>= 2) 146 ctxt.too_expensive <<= 1; 147 if (ctxt.too_expensive < 256) 148 ctxt.too_expensive = 256; 149 150 /* Allocate memory for fdiag and bdiag from a thread-local pool. */ 151 fdiag_len = xvec_length + yvec_length + 3; 152 gl_once (keys_init_once, keys_init); 153 buffer = (int *) gl_tls_get (buffer_key); 154 bufmax = (size_t) (uintptr_t) gl_tls_get (bufmax_key); 155 if (fdiag_len > bufmax) 156 { 157 /* Need more memory. */ 158 bufmax = 2 * bufmax; 159 if (fdiag_len > bufmax) 160 bufmax = fdiag_len; 161 /* Calling xrealloc would be a waste: buffer's contents does not need 162 to be preserved. */ 163 if (buffer != NULL) 164 free (buffer); 165 buffer = (int *) xnmalloc (bufmax, 2 * sizeof (int)); 166 gl_tls_set (buffer_key, buffer); 167 gl_tls_set (bufmax_key, (void *) (uintptr_t) bufmax); 168 } 169 ctxt.fdiag = buffer + yvec_length + 1; 170 ctxt.bdiag = ctxt.fdiag + fdiag_len; 171 172 /* Now do the main comparison algorithm */ 173 ctxt.xvec_edit_count = 0; 174 ctxt.yvec_edit_count = 0; 175 compareseq (0, xvec_length, 0, yvec_length, 0, 176 &ctxt); 177 178 /* The result is 179 ((number of chars in common) / (average length of the strings)). 180 This is admittedly biased towards finding that the strings are 181 similar, however it does produce meaningful results. */ 182 return ((double) (xvec_length + yvec_length 183 - ctxt.yvec_edit_count - ctxt.xvec_edit_count) 184 / (xvec_length + yvec_length)); 185} 186