You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
637 lines
15 KiB
637 lines
15 KiB
/* Functions to make fuzzy comparisons between strings
|
|
Copyright (C) 1988, 1989, 1992, 1993, 1995 Free Software Foundation, Inc.
|
|
|
|
This program is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2 of the License, or (at
|
|
your option) any later version.
|
|
|
|
This program is distributed in the hope that it will be useful, but
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program; if not, write to the Free Software
|
|
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
|
|
|
|
|
|
Derived from GNU diff 2.7, analyze.c et al.
|
|
|
|
The basic algorithm is described in:
|
|
"An O(ND) Difference Algorithm and its Variations", Eugene Myers,
|
|
Algorithmica Vol. 1 No. 2, 1986, pp. 251-266;
|
|
see especially section 4.2, which describes the variation used below.
|
|
|
|
The basic algorithm was independently discovered as described in:
|
|
"Algorithms for Approximate String Matching", E. Ukkonen,
|
|
Information and Control Vol. 64, 1985, pp. 100-118.
|
|
|
|
Modified to work on strings rather than files
|
|
by Peter Miller <pmiller@agso.gov.au>, October 1995 */
|
|
|
|
#ifdef HAVE_CONFIG_H
|
|
# include "config.h"
|
|
#endif
|
|
|
|
#ifdef HAVE_STRING_H
|
|
# include <string.h>
|
|
#else
|
|
# include <strings.h>
|
|
#endif
|
|
|
|
#include <stdio.h>
|
|
|
|
#ifdef HAVE_LIMITS_H
|
|
# include <limits.h>
|
|
#else
|
|
# define INT_MAX ((int)(~(unsigned)0 >> 1))
|
|
#endif
|
|
|
|
#include "system.h"
|
|
#include "fstrcmp.h"
|
|
|
|
|
|
/*
|
|
* Data on one input string being compared.
|
|
*/
|
|
struct string_data
|
|
{
|
|
/* The string to be compared. */
|
|
const char *data;
|
|
|
|
/* The length of the string to be compared. */
|
|
int data_length;
|
|
|
|
/* The number of characters inserted or deleted. */
|
|
int edit_count;
|
|
};
|
|
|
|
static struct string_data string[2];
|
|
|
|
|
|
#ifdef MINUS_H_FLAG
|
|
|
|
/* This corresponds to the diff -H flag. With this heuristic, for
|
|
strings with a constant small density of changes, the algorithm is
|
|
linear in the strings size. This is unlikely in typical uses of
|
|
fstrcmp, and so is usually compiled out. Besides, there is no
|
|
interface to set it true. */
|
|
static int heuristic;
|
|
|
|
#endif
|
|
|
|
|
|
/* Vector, indexed by diagonal, containing 1 + the X coordinate of the
|
|
point furthest along the given diagonal in the forward search of the
|
|
edit matrix. */
|
|
static int *fdiag;
|
|
|
|
/* Vector, indexed by diagonal, containing the X coordinate of the point
|
|
furthest along the given diagonal in the backward search of the edit
|
|
matrix. */
|
|
static int *bdiag;
|
|
|
|
/* Edit scripts longer than this are too expensive to compute. */
|
|
static int too_expensive;
|
|
|
|
/* Snakes bigger than this are considered `big'. */
|
|
#define SNAKE_LIMIT 20
|
|
|
|
struct partition
|
|
{
|
|
/* Midpoints of this partition. */
|
|
int xmid, ymid;
|
|
|
|
/* Nonzero if low half will be analyzed minimally. */
|
|
int lo_minimal;
|
|
|
|
/* Likewise for high half. */
|
|
int hi_minimal;
|
|
};
|
|
|
|
|
|
/* NAME
|
|
diag - find diagonal path
|
|
|
|
SYNOPSIS
|
|
int diag(int xoff, int xlim, int yoff, int ylim, int minimal,
|
|
struct partition *part);
|
|
|
|
DESCRIPTION
|
|
Find the midpoint of the shortest edit script for a specified
|
|
portion of the two strings.
|
|
|
|
Scan from the beginnings of the strings, and simultaneously from
|
|
the ends, doing a breadth-first search through the space of
|
|
edit-sequence. When the two searches meet, we have found the
|
|
midpoint of the shortest edit sequence.
|
|
|
|
If MINIMAL is nonzero, find the minimal edit script regardless
|
|
of expense. Otherwise, if the search is too expensive, use
|
|
heuristics to stop the search and report a suboptimal answer.
|
|
|
|
RETURNS
|
|
Set PART->(XMID,YMID) to the midpoint (XMID,YMID). The diagonal
|
|
number XMID - YMID equals the number of inserted characters
|
|
minus the number of deleted characters (counting only characters
|
|
before the midpoint). Return the approximate edit cost; this is
|
|
the total number of characters inserted or deleted (counting
|
|
only characters before the midpoint), unless a heuristic is used
|
|
to terminate the search prematurely.
|
|
|
|
Set PART->LEFT_MINIMAL to nonzero iff the minimal edit script
|
|
for the left half of the partition is known; similarly for
|
|
PART->RIGHT_MINIMAL.
|
|
|
|
CAVEAT
|
|
This function assumes that the first characters of the specified
|
|
portions of the two strings do not match, and likewise that the
|
|
last characters do not match. The caller must trim matching
|
|
characters from the beginning and end of the portions it is
|
|
going to specify.
|
|
|
|
If we return the "wrong" partitions, the worst this can do is
|
|
cause suboptimal diff output. It cannot cause incorrect diff
|
|
output. */
|
|
|
|
static int diag PARAMS ((int, int, int, int, int, struct partition *));
|
|
|
|
static int
|
|
diag (xoff, xlim, yoff, ylim, minimal, part)
|
|
int xoff;
|
|
int xlim;
|
|
int yoff;
|
|
int ylim;
|
|
int minimal;
|
|
struct partition *part;
|
|
{
|
|
int *const fd = fdiag; /* Give the compiler a chance. */
|
|
int *const bd = bdiag; /* Additional help for the compiler. */
|
|
const char *const xv = string[0].data; /* Still more help for the compiler. */
|
|
const char *const yv = string[1].data; /* And more and more . . . */
|
|
const int dmin = xoff - ylim; /* Minimum valid diagonal. */
|
|
const int dmax = xlim - yoff; /* Maximum valid diagonal. */
|
|
const int fmid = xoff - yoff; /* Center diagonal of top-down search. */
|
|
const int bmid = xlim - ylim; /* Center diagonal of bottom-up search. */
|
|
int fmin = fmid;
|
|
int fmax = fmid; /* Limits of top-down search. */
|
|
int bmin = bmid;
|
|
int bmax = bmid; /* Limits of bottom-up search. */
|
|
int c; /* Cost. */
|
|
int odd = (fmid - bmid) & 1;
|
|
|
|
/*
|
|
* True if southeast corner is on an odd diagonal with respect
|
|
* to the northwest.
|
|
*/
|
|
fd[fmid] = xoff;
|
|
bd[bmid] = xlim;
|
|
for (c = 1;; ++c)
|
|
{
|
|
int d; /* Active diagonal. */
|
|
int big_snake;
|
|
|
|
big_snake = 0;
|
|
/* Extend the top-down search by an edit step in each diagonal. */
|
|
if (fmin > dmin)
|
|
fd[--fmin - 1] = -1;
|
|
else
|
|
++fmin;
|
|
if (fmax < dmax)
|
|
fd[++fmax + 1] = -1;
|
|
else
|
|
--fmax;
|
|
for (d = fmax; d >= fmin; d -= 2)
|
|
{
|
|
int x;
|
|
int y;
|
|
int oldx;
|
|
int tlo;
|
|
int thi;
|
|
|
|
tlo = fd[d - 1],
|
|
thi = fd[d + 1];
|
|
|
|
if (tlo >= thi)
|
|
x = tlo + 1;
|
|
else
|
|
x = thi;
|
|
oldx = x;
|
|
y = x - d;
|
|
while (x < xlim && y < ylim && xv[x] == yv[y])
|
|
{
|
|
++x;
|
|
++y;
|
|
}
|
|
if (x - oldx > SNAKE_LIMIT)
|
|
big_snake = 1;
|
|
fd[d] = x;
|
|
if (odd && bmin <= d && d <= bmax && bd[d] <= x)
|
|
{
|
|
part->xmid = x;
|
|
part->ymid = y;
|
|
part->lo_minimal = part->hi_minimal = 1;
|
|
return 2 * c - 1;
|
|
}
|
|
}
|
|
/* Similarly extend the bottom-up search. */
|
|
if (bmin > dmin)
|
|
bd[--bmin - 1] = INT_MAX;
|
|
else
|
|
++bmin;
|
|
if (bmax < dmax)
|
|
bd[++bmax + 1] = INT_MAX;
|
|
else
|
|
--bmax;
|
|
for (d = bmax; d >= bmin; d -= 2)
|
|
{
|
|
int x;
|
|
int y;
|
|
int oldx;
|
|
int tlo;
|
|
int thi;
|
|
|
|
tlo = bd[d - 1],
|
|
thi = bd[d + 1];
|
|
if (tlo < thi)
|
|
x = tlo;
|
|
else
|
|
x = thi - 1;
|
|
oldx = x;
|
|
y = x - d;
|
|
while (x > xoff && y > yoff && xv[x - 1] == yv[y - 1])
|
|
{
|
|
--x;
|
|
--y;
|
|
}
|
|
if (oldx - x > SNAKE_LIMIT)
|
|
big_snake = 1;
|
|
bd[d] = x;
|
|
if (!odd && fmin <= d && d <= fmax && x <= fd[d])
|
|
{
|
|
part->xmid = x;
|
|
part->ymid = y;
|
|
part->lo_minimal = part->hi_minimal = 1;
|
|
return 2 * c;
|
|
}
|
|
}
|
|
|
|
if (minimal)
|
|
continue;
|
|
|
|
#ifdef MINUS_H_FLAG
|
|
/* Heuristic: check occasionally for a diagonal that has made lots
|
|
of progress compared with the edit distance. If we have any
|
|
such, find the one that has made the most progress and return
|
|
it as if it had succeeded.
|
|
|
|
With this heuristic, for strings with a constant small density
|
|
of changes, the algorithm is linear in the strings size. */
|
|
if (c > 200 && big_snake && heuristic)
|
|
{
|
|
int best;
|
|
|
|
best = 0;
|
|
for (d = fmax; d >= fmin; d -= 2)
|
|
{
|
|
int dd;
|
|
int x;
|
|
int y;
|
|
int v;
|
|
|
|
dd = d - fmid;
|
|
x = fd[d];
|
|
y = x - d;
|
|
v = (x - xoff) * 2 - dd;
|
|
|
|
if (v > 12 * (c + (dd < 0 ? -dd : dd)))
|
|
{
|
|
if
|
|
(
|
|
v > best
|
|
&&
|
|
xoff + SNAKE_LIMIT <= x
|
|
&&
|
|
x < xlim
|
|
&&
|
|
yoff + SNAKE_LIMIT <= y
|
|
&&
|
|
y < ylim
|
|
)
|
|
{
|
|
/* We have a good enough best diagonal; now insist
|
|
that it end with a significant snake. */
|
|
int k;
|
|
|
|
for (k = 1; xv[x - k] == yv[y - k]; k++)
|
|
{
|
|
if (k == SNAKE_LIMIT)
|
|
{
|
|
best = v;
|
|
part->xmid = x;
|
|
part->ymid = y;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
if (best > 0)
|
|
{
|
|
part->lo_minimal = 1;
|
|
part->hi_minimal = 0;
|
|
return 2 * c - 1;
|
|
}
|
|
best = 0;
|
|
for (d = bmax; d >= bmin; d -= 2)
|
|
{
|
|
int dd;
|
|
int x;
|
|
int y;
|
|
int v;
|
|
|
|
dd = d - bmid;
|
|
x = bd[d];
|
|
y = x - d;
|
|
v = (xlim - x) * 2 + dd;
|
|
|
|
if (v > 12 * (c + (dd < 0 ? -dd : dd)))
|
|
{
|
|
if (v > best && xoff < x && x <= xlim - SNAKE_LIMIT &&
|
|
yoff < y && y <= ylim - SNAKE_LIMIT)
|
|
{
|
|
/* We have a good enough best diagonal; now insist
|
|
that it end with a significant snake. */
|
|
int k;
|
|
|
|
for (k = 0; xv[x + k] == yv[y + k]; k++)
|
|
{
|
|
if (k == SNAKE_LIMIT - 1)
|
|
{
|
|
best = v;
|
|
part->xmid = x;
|
|
part->ymid = y;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
if (best > 0)
|
|
{
|
|
part->lo_minimal = 0;
|
|
part->hi_minimal = 1;
|
|
return 2 * c - 1;
|
|
}
|
|
}
|
|
#endif /* MINUS_H_FLAG */
|
|
|
|
/* Heuristic: if we've gone well beyond the call of duty, give up
|
|
and report halfway between our best results so far. */
|
|
if (c >= too_expensive)
|
|
{
|
|
int fxybest;
|
|
int fxbest;
|
|
int bxybest;
|
|
int bxbest;
|
|
|
|
/* Pacify `gcc -Wall'. */
|
|
fxbest = 0;
|
|
bxbest = 0;
|
|
|
|
/* Find forward diagonal that maximizes X + Y. */
|
|
fxybest = -1;
|
|
for (d = fmax; d >= fmin; d -= 2)
|
|
{
|
|
int x;
|
|
int y;
|
|
|
|
x = fd[d] < xlim ? fd[d] : xlim;
|
|
y = x - d;
|
|
|
|
if (ylim < y)
|
|
{
|
|
x = ylim + d;
|
|
y = ylim;
|
|
}
|
|
if (fxybest < x + y)
|
|
{
|
|
fxybest = x + y;
|
|
fxbest = x;
|
|
}
|
|
}
|
|
/* Find backward diagonal that minimizes X + Y. */
|
|
bxybest = INT_MAX;
|
|
for (d = bmax; d >= bmin; d -= 2)
|
|
{
|
|
int x;
|
|
int y;
|
|
|
|
x = xoff > bd[d] ? xoff : bd[d];
|
|
y = x - d;
|
|
|
|
if (y < yoff)
|
|
{
|
|
x = yoff + d;
|
|
y = yoff;
|
|
}
|
|
if (x + y < bxybest)
|
|
{
|
|
bxybest = x + y;
|
|
bxbest = x;
|
|
}
|
|
}
|
|
/* Use the better of the two diagonals. */
|
|
if ((xlim + ylim) - bxybest < fxybest - (xoff + yoff))
|
|
{
|
|
part->xmid = fxbest;
|
|
part->ymid = fxybest - fxbest;
|
|
part->lo_minimal = 1;
|
|
part->hi_minimal = 0;
|
|
}
|
|
else
|
|
{
|
|
part->xmid = bxbest;
|
|
part->ymid = bxybest - bxbest;
|
|
part->lo_minimal = 0;
|
|
part->hi_minimal = 1;
|
|
}
|
|
return 2 * c - 1;
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
/* NAME
|
|
compareseq - find edit sequence
|
|
|
|
SYNOPSIS
|
|
void compareseq(int xoff, int xlim, int yoff, int ylim, int minimal);
|
|
|
|
DESCRIPTION
|
|
Compare in detail contiguous subsequences of the two strings
|
|
which are known, as a whole, to match each other.
|
|
|
|
The subsequence of string 0 is [XOFF, XLIM) and likewise for
|
|
string 1.
|
|
|
|
Note that XLIM, YLIM are exclusive bounds. All character
|
|
numbers are origin-0.
|
|
|
|
If MINIMAL is nonzero, find a minimal difference no matter how
|
|
expensive it is. */
|
|
|
|
static void compareseq PARAMS ((int, int, int, int, int));
|
|
|
|
static void
|
|
compareseq (xoff, xlim, yoff, ylim, minimal)
|
|
int xoff;
|
|
int xlim;
|
|
int yoff;
|
|
int ylim;
|
|
int minimal;
|
|
{
|
|
const char *const xv = string[0].data; /* Help the compiler. */
|
|
const char *const yv = string[1].data;
|
|
|
|
/* Slide down the bottom initial diagonal. */
|
|
while (xoff < xlim && yoff < ylim && xv[xoff] == yv[yoff])
|
|
{
|
|
++xoff;
|
|
++yoff;
|
|
}
|
|
|
|
/* Slide up the top initial diagonal. */
|
|
while (xlim > xoff && ylim > yoff && xv[xlim - 1] == yv[ylim - 1])
|
|
{
|
|
--xlim;
|
|
--ylim;
|
|
}
|
|
|
|
/* Handle simple cases. */
|
|
if (xoff == xlim)
|
|
{
|
|
while (yoff < ylim)
|
|
{
|
|
++string[1].edit_count;
|
|
++yoff;
|
|
}
|
|
}
|
|
else if (yoff == ylim)
|
|
{
|
|
while (xoff < xlim)
|
|
{
|
|
++string[0].edit_count;
|
|
++xoff;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
int c;
|
|
struct partition part;
|
|
|
|
/* Find a point of correspondence in the middle of the strings. */
|
|
c = diag (xoff, xlim, yoff, ylim, minimal, &part);
|
|
if (c == 1)
|
|
{
|
|
#if 0
|
|
/* This should be impossible, because it implies that one of
|
|
the two subsequences is empty, and that case was handled
|
|
above without calling `diag'. Let's verify that this is
|
|
true. */
|
|
abort ();
|
|
#else
|
|
/* The two subsequences differ by a single insert or delete;
|
|
record it and we are done. */
|
|
if (part.xmid - part.ymid < xoff - yoff)
|
|
++string[1].edit_count;
|
|
else
|
|
++string[0].edit_count;
|
|
#endif
|
|
}
|
|
else
|
|
{
|
|
/* Use the partitions to split this problem into subproblems. */
|
|
compareseq (xoff, part.xmid, yoff, part.ymid, part.lo_minimal);
|
|
compareseq (part.xmid, xlim, part.ymid, ylim, part.hi_minimal);
|
|
}
|
|
}
|
|
}
|
|
|
|
|
|
/* NAME
|
|
fstrcmp - fuzzy string compare
|
|
|
|
SYNOPSIS
|
|
double fstrcmp(const char *, const char *);
|
|
|
|
DESCRIPTION
|
|
The fstrcmp function may be used to compare two string for
|
|
similarity. It is very useful in reducing "cascade" or
|
|
"secondary" errors in compilers or other situations where
|
|
symbol tables occur.
|
|
|
|
RETURNS
|
|
double; 0 if the strings are entirly dissimilar, 1 if the
|
|
strings are identical, and a number in between if they are
|
|
similar. */
|
|
|
|
double
|
|
fstrcmp (string1, string2)
|
|
const char *string1;
|
|
const char *string2;
|
|
{
|
|
int i;
|
|
|
|
size_t fdiag_len;
|
|
static int *fdiag_buf;
|
|
static size_t fdiag_max;
|
|
|
|
/* set the info for each string. */
|
|
string[0].data = string1;
|
|
string[0].data_length = strlen (string1);
|
|
string[1].data = string2;
|
|
string[1].data_length = strlen (string2);
|
|
|
|
/* short-circuit obvious comparisons */
|
|
if (string[0].data_length == 0 && string[1].data_length == 0)
|
|
return 1.0;
|
|
if (string[0].data_length == 0 || string[1].data_length == 0)
|
|
return 0.0;
|
|
|
|
/* Set TOO_EXPENSIVE to be approximate square root of input size,
|
|
bounded below by 256. */
|
|
too_expensive = 1;
|
|
for (i = string[0].data_length + string[1].data_length; i != 0; i >>= 2)
|
|
too_expensive <<= 1;
|
|
if (too_expensive < 256)
|
|
too_expensive = 256;
|
|
|
|
/* Because fstrcmp is typically called multiple times, while scanning
|
|
symbol tables, etc, attempt to minimize the number of memory
|
|
allocations performed. Thus, we use a static buffer for the
|
|
diagonal vectors, and never free them. */
|
|
fdiag_len = string[0].data_length + string[1].data_length + 3;
|
|
if (fdiag_len > fdiag_max)
|
|
{
|
|
fdiag_max = fdiag_len;
|
|
fdiag_buf = xrealloc (fdiag_buf, fdiag_max * (2 * sizeof (int)));
|
|
}
|
|
fdiag = fdiag_buf + string[1].data_length + 1;
|
|
bdiag = fdiag + fdiag_len;
|
|
|
|
/* Now do the main comparison algorithm */
|
|
string[0].edit_count = 0;
|
|
string[1].edit_count = 0;
|
|
compareseq (0, string[0].data_length, 0, string[1].data_length, 0);
|
|
|
|
/* The result is
|
|
((number of chars in common) / (average length of the strings)).
|
|
This is admittedly biased towards finding that the strings are
|
|
similar, however it does produce meaningful results. */
|
|
return ((double) (string[0].data_length + string[1].data_length -
|
|
string[1].edit_count - string[0].edit_count) / (string[0].data_length
|
|
+ string[1].data_length));
|
|
}
|