String-Similarity/fstrcmp.c

/* 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

   Modified to accept a "minimum similarity limit" to stop analyzing the
   string when the similarity drops below the given limit by Marc Lehmann
   <schmorp@schmorp.de>.

   Modified to work on unicode (actually 31 bit are allowed) by Marc Lehmann
   <schmorp@schmorp.de>.
*/

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

#include "fstrcmp.h"

/* moved here from fstrcmp.h to avoid problems on lose32 machines */
#define PARAMS(proto) proto
typedef UV CHAR;

/*
 * 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];

static int max_edits; /* compareseq stops when edits > max_edits */

#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;

  if (string[1].edit_count + string[0].edit_count > max_edits)
    return;

  /* 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 *s1, int l1, const CHAR *s2, int l2, double);

   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 (const CHAR *string1, int length1,
         const CHAR *string2, int length2,
         double minimum)
{
  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 = length1;
  string[1].data = string2;
  string[1].data_length = length2;

  /* 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 = realloc (fdiag_buf, fdiag_max * (2 * sizeof (int)));
    }
  fdiag = fdiag_buf + string[1].data_length + 1;
  bdiag = fdiag + fdiag_len;

  max_edits = 1 + (string[0].data_length + string[1].data_length) * (1. - minimum);

  /* 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));

}
Revision:	1.1
Committed:	Sat Jun 25 09:55:53 2005 UTC (19 years ago) by root
Content type:	text/plain
Branch:	MAIN
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	/* Functions to make fuzzy comparisons between strings
2			Copyright (C) 1988, 1989, 1992, 1993, 1995 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 2 of the License, or (at
7			your option) any later version.
8
9			This program is distributed in the hope that it will be useful, but
10			WITHOUT ANY WARRANTY; without even the implied warranty of
11			MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12			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, write to the Free Software
16			Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
17
18
19			Derived from GNU diff 2.7, analyze.c et al.
20
21			The basic algorithm is described in:
22			"An O(ND) Difference Algorithm and its Variations", Eugene Myers,
23			Algorithmica Vol. 1 No. 2, 1986, pp. 251-266;
24			see especially section 4.2, which describes the variation used below.
25
26			The basic algorithm was independently discovered as described in:
27			"Algorithms for Approximate String Matching", E. Ukkonen,
28			Information and Control Vol. 64, 1985, pp. 100-118.
29
30			Modified to work on strings rather than files
31			by Peter Miller <pmiller@agso.gov.au>, October 1995
32
33			Modified to accept a "minimum similarity limit" to stop analyzing the
34			string when the similarity drops below the given limit by Marc Lehmann
35			<schmorp@schmorp.de>.
36
37			Modified to work on unicode (actually 31 bit are allowed) by Marc Lehmann
38			<schmorp@schmorp.de>.
39			*/
40
41			#include <string.h>
42			#include <stdio.h>
43			#include <stdlib.h>
44			#include <limits.h>
45
46			#include "fstrcmp.h"
47
48			/* moved here from fstrcmp.h to avoid problems on lose32 machines */
49			#define PARAMS(proto) proto
50			typedef UV CHAR;
51
52			/*
53			* Data on one input string being compared.
54			*/
55			struct string_data
56			{
57			/* The string to be compared. */
58			const CHAR *data;
59
60			/* The length of the string to be compared. */
61			int data_length;
62
63			/* The number of characters inserted or deleted. */
64			int edit_count;
65			};
66
67			static struct string_data string[2];
68
69			static int max_edits; /* compareseq stops when edits > max_edits */
70
71			#ifdef MINUS_H_FLAG
72
73			/* This corresponds to the diff -H flag. With this heuristic, for
74			strings with a constant small density of changes, the algorithm is
75			linear in the strings size. This is unlikely in typical uses of
76			fstrcmp, and so is usually compiled out. Besides, there is no
77			interface to set it true. */
78			static int heuristic;
79
80			#endif
81
82
83			/* Vector, indexed by diagonal, containing 1 + the X coordinate of the
84			point furthest along the given diagonal in the forward search of the
85			edit matrix. */
86			static int *fdiag;
87
88			/* Vector, indexed by diagonal, containing the X coordinate of the point
89			furthest along the given diagonal in the backward search of the edit
90			matrix. */
91			static int *bdiag;
92
93			/* Edit scripts longer than this are too expensive to compute. */
94			static int too_expensive;
95
96			/* Snakes bigger than this are considered `big'. */
97			#define SNAKE_LIMIT 20
98
99			struct partition
100			{
101			/* Midpoints of this partition. */
102			int xmid, ymid;
103
104			/* Nonzero if low half will be analyzed minimally. */
105			int lo_minimal;
106
107			/* Likewise for high half. */
108			int hi_minimal;
109			};
110
111
112			/* NAME
113			diag - find diagonal path
114
115			SYNOPSIS
116			int diag(int xoff, int xlim, int yoff, int ylim, int minimal,
117			struct partition *part);
118
119			DESCRIPTION
120			Find the midpoint of the shortest edit script for a specified
121			portion of the two strings.
122
123			Scan from the beginnings of the strings, and simultaneously from
124			the ends, doing a breadth-first search through the space of
125			edit-sequence. When the two searches meet, we have found the
126			midpoint of the shortest edit sequence.
127
128			If MINIMAL is nonzero, find the minimal edit script regardless
129			of expense. Otherwise, if the search is too expensive, use
130			heuristics to stop the search and report a suboptimal answer.
131
132			RETURNS
133			Set PART->(XMID,YMID) to the midpoint (XMID,YMID). The diagonal
134			number XMID - YMID equals the number of inserted characters
135			minus the number of deleted characters (counting only characters
136			before the midpoint). Return the approximate edit cost; this is
137			the total number of characters inserted or deleted (counting
138			only characters before the midpoint), unless a heuristic is used
139			to terminate the search prematurely.
140
141			Set PART->LEFT_MINIMAL to nonzero iff the minimal edit script
142			for the left half of the partition is known; similarly for
143			PART->RIGHT_MINIMAL.
144
145			CAVEAT
146			This function assumes that the first characters of the specified
147			portions of the two strings do not match, and likewise that the
148			last characters do not match. The caller must trim matching
149			characters from the beginning and end of the portions it is
150			going to specify.
151
152			If we return the "wrong" partitions, the worst this can do is
153			cause suboptimal diff output. It cannot cause incorrect diff
154			output. */
155
156			static int diag PARAMS ((int, int, int, int, int, struct partition *));
157
158			static int
159			diag (xoff, xlim, yoff, ylim, minimal, part)
160			int xoff;
161			int xlim;
162			int yoff;
163			int ylim;
164			int minimal;
165			struct partition *part;
166			{
167			int const fd = fdiag; / Give the compiler a chance. */
168			int const bd = bdiag; / Additional help for the compiler. */
169			const CHAR const xv = string[0].data; / Still more help for the compiler. */
170			const CHAR const yv = string[1].data; / And more and more . . . */
171			const int dmin = xoff - ylim; /* Minimum valid diagonal. */
172			const int dmax = xlim - yoff; /* Maximum valid diagonal. */
173			const int fmid = xoff - yoff; /* Center diagonal of top-down search. */
174			const int bmid = xlim - ylim; /* Center diagonal of bottom-up search. */
175			int fmin = fmid;
176			int fmax = fmid; /* Limits of top-down search. */
177			int bmin = bmid;
178			int bmax = bmid; /* Limits of bottom-up search. */
179			int c; /* Cost. */
180			int odd = (fmid - bmid) & 1;
181
182			/*
183			* True if southeast corner is on an odd diagonal with respect
184			* to the northwest.
185			*/
186			fd[fmid] = xoff;
187			bd[bmid] = xlim;
188			for (c = 1;; ++c)
189			{
190			int d; /* Active diagonal. */
191			int big_snake;
192
193			big_snake = 0;
194			/* Extend the top-down search by an edit step in each diagonal. */
195			if (fmin > dmin)
196			fd[--fmin - 1] = -1;
197			else
198			++fmin;
199			if (fmax < dmax)
200			fd[++fmax + 1] = -1;
201			else
202			--fmax;
203			for (d = fmax; d >= fmin; d -= 2)
204			{
205			int x;
206			int y;
207			int oldx;
208			int tlo;
209			int thi;
210
211			tlo = fd[d - 1],
212			thi = fd[d + 1];
213
214			if (tlo >= thi)
215			x = tlo + 1;
216			else
217			x = thi;
218			oldx = x;
219			y = x - d;
220			while (x < xlim && y < ylim && xv[x] == yv[y])
221			{
222			++x;
223			++y;
224			}
225			if (x - oldx > SNAKE_LIMIT)
226			big_snake = 1;
227			fd[d] = x;
228			if (odd && bmin <= d && d <= bmax && bd[d] <= x)
229			{
230			part->xmid = x;
231			part->ymid = y;
232			part->lo_minimal = part->hi_minimal = 1;
233			return 2 * c - 1;
234			}
235			}
236			/* Similarly extend the bottom-up search. */
237			if (bmin > dmin)
238			bd[--bmin - 1] = INT_MAX;
239			else
240			++bmin;
241			if (bmax < dmax)
242			bd[++bmax + 1] = INT_MAX;
243			else
244			--bmax;
245			for (d = bmax; d >= bmin; d -= 2)
246			{
247			int x;
248			int y;
249			int oldx;
250			int tlo;
251			int thi;
252
253			tlo = bd[d - 1],
254			thi = bd[d + 1];
255			if (tlo < thi)
256			x = tlo;
257			else
258			x = thi - 1;
259			oldx = x;
260			y = x - d;
261			while (x > xoff && y > yoff && xv[x - 1] == yv[y - 1])
262			{
263			--x;
264			--y;
265			}
266			if (oldx - x > SNAKE_LIMIT)
267			big_snake = 1;
268			bd[d] = x;
269			if (!odd && fmin <= d && d <= fmax && x <= fd[d])
270			{
271			part->xmid = x;
272			part->ymid = y;
273			part->lo_minimal = part->hi_minimal = 1;
274			return 2 * c;
275			}
276			}
277
278			if (minimal)
279			continue;
280
281			#ifdef MINUS_H_FLAG
282			/* Heuristic: check occasionally for a diagonal that has made lots
283			of progress compared with the edit distance. If we have any
284			such, find the one that has made the most progress and return
285			it as if it had succeeded.
286
287			With this heuristic, for strings with a constant small density
288			of changes, the algorithm is linear in the strings size. */
289			if (c > 200 && big_snake && heuristic)
290			{
291			int best;
292
293			best = 0;
294			for (d = fmax; d >= fmin; d -= 2)
295			{
296			int dd;
297			int x;
298			int y;
299			int v;
300
301			dd = d - fmid;
302			x = fd[d];
303			y = x - d;
304			v = (x - xoff) * 2 - dd;
305
306			if (v > 12 * (c + (dd < 0 ? -dd : dd)))
307			{
308			if
309			(
310			v > best
311			&&
312			xoff + SNAKE_LIMIT <= x
313			&&
314			x < xlim
315			&&
316			yoff + SNAKE_LIMIT <= y
317			&&
318			y < ylim
319			)
320			{
321			/* We have a good enough best diagonal; now insist
322			that it end with a significant snake. */
323			int k;
324
325			for (k = 1; xv[x - k] == yv[y - k]; k++)
326			{
327			if (k == SNAKE_LIMIT)
328			{
329			best = v;
330			part->xmid = x;
331			part->ymid = y;
332			break;
333			}
334			}
335			}
336			}
337			}
338			if (best > 0)
339			{
340			part->lo_minimal = 1;
341			part->hi_minimal = 0;
342			return 2 * c - 1;
343			}
344			best = 0;
345			for (d = bmax; d >= bmin; d -= 2)
346			{
347			int dd;
348			int x;
349			int y;
350			int v;
351
352			dd = d - bmid;
353			x = bd[d];
354			y = x - d;
355			v = (xlim - x) * 2 + dd;
356
357			if (v > 12 * (c + (dd < 0 ? -dd : dd)))
358			{
359			if (v > best && xoff < x && x <= xlim - SNAKE_LIMIT &&
360			yoff < y && y <= ylim - SNAKE_LIMIT)
361			{
362			/* We have a good enough best diagonal; now insist
363			that it end with a significant snake. */
364			int k;
365
366			for (k = 0; xv[x + k] == yv[y + k]; k++)
367			{
368			if (k == SNAKE_LIMIT - 1)
369			{
370			best = v;
371			part->xmid = x;
372			part->ymid = y;
373			break;
374			}
375			}
376			}
377			}
378			}
379			if (best > 0)
380			{
381			part->lo_minimal = 0;
382			part->hi_minimal = 1;
383			return 2 * c - 1;
384			}
385			}
386			#endif /* MINUS_H_FLAG */
387
388			/* Heuristic: if we've gone well beyond the call of duty, give up
389			and report halfway between our best results so far. */
390			if (c >= too_expensive)
391			{
392			int fxybest;
393			int fxbest;
394			int bxybest;
395			int bxbest;
396
397			/* Pacify `gcc -Wall'. */
398			fxbest = 0;
399			bxbest = 0;
400
401			/* Find forward diagonal that maximizes X + Y. */
402			fxybest = -1;
403			for (d = fmax; d >= fmin; d -= 2)
404			{
405			int x;
406			int y;
407
408			x = fd[d] < xlim ? fd[d] : xlim;
409			y = x - d;
410
411			if (ylim < y)
412			{
413			x = ylim + d;
414			y = ylim;
415			}
416			if (fxybest < x + y)
417			{
418			fxybest = x + y;
419			fxbest = x;
420			}
421			}
422			/* Find backward diagonal that minimizes X + Y. */
423			bxybest = INT_MAX;
424			for (d = bmax; d >= bmin; d -= 2)
425			{
426			int x;
427			int y;
428
429			x = xoff > bd[d] ? xoff : bd[d];
430			y = x - d;
431
432			if (y < yoff)
433			{
434			x = yoff + d;
435			y = yoff;
436			}
437			if (x + y < bxybest)
438			{
439			bxybest = x + y;
440			bxbest = x;
441			}
442			}
443			/* Use the better of the two diagonals. */
444			if ((xlim + ylim) - bxybest < fxybest - (xoff + yoff))
445			{
446			part->xmid = fxbest;
447			part->ymid = fxybest - fxbest;
448			part->lo_minimal = 1;
449			part->hi_minimal = 0;
450			}
451			else
452			{
453			part->xmid = bxbest;
454			part->ymid = bxybest - bxbest;
455			part->lo_minimal = 0;
456			part->hi_minimal = 1;
457			}
458			return 2 * c - 1;
459			}
460			}
461			}
462
463
464			/* NAME
465			compareseq - find edit sequence
466
467			SYNOPSIS
468			void compareseq(int xoff, int xlim, int yoff, int ylim, int minimal);
469
470			DESCRIPTION
471			Compare in detail contiguous subsequences of the two strings
472			which are known, as a whole, to match each other.
473
474			The subsequence of string 0 is [XOFF, XLIM) and likewise for
475			string 1.
476
477			Note that XLIM, YLIM are exclusive bounds. All character
478			numbers are origin-0.
479
480			If MINIMAL is nonzero, find a minimal difference no matter how
481			expensive it is. */
482
483			static void compareseq PARAMS ((int, int, int, int, int));
484
485			static void
486			compareseq (xoff, xlim, yoff, ylim, minimal)
487			int xoff;
488			int xlim;
489			int yoff;
490			int ylim;
491			int minimal;
492			{
493			const CHAR const xv = string[0].data; / Help the compiler. */
494			const CHAR *const yv = string[1].data;
495
496			if (string[1].edit_count + string[0].edit_count > max_edits)
497			return;
498
499			/* Slide down the bottom initial diagonal. */
500			while (xoff < xlim && yoff < ylim && xv[xoff] == yv[yoff])
501			{
502			++xoff;
503			++yoff;
504			}
505
506			/* Slide up the top initial diagonal. */
507			while (xlim > xoff && ylim > yoff && xv[xlim - 1] == yv[ylim - 1])
508			{
509			--xlim;
510			--ylim;
511			}
512
513			/* Handle simple cases. */
514			if (xoff == xlim)
515			{
516			while (yoff < ylim)
517			{
518			++string[1].edit_count;
519			++yoff;
520			}
521			}
522			else if (yoff == ylim)
523			{
524			while (xoff < xlim)
525			{
526			++string[0].edit_count;
527			++xoff;
528			}
529			}
530			else
531			{
532			int c;
533			struct partition part;
534
535			/* Find a point of correspondence in the middle of the strings. */
536			c = diag (xoff, xlim, yoff, ylim, minimal, &part);
537			if (c == 1)
538			{
539			#if 0
540			/* This should be impossible, because it implies that one of
541			the two subsequences is empty, and that case was handled
542			above without calling `diag'. Let's verify that this is
543			true. */
544			abort ();
545			#else
546			/* The two subsequences differ by a single insert or delete;
547			record it and we are done. */
548			if (part.xmid - part.ymid < xoff - yoff)
549			++string[1].edit_count;
550			else
551			++string[0].edit_count;
552			#endif
553			}
554			else
555			{
556			/* Use the partitions to split this problem into subproblems. */
557			compareseq (xoff, part.xmid, yoff, part.ymid, part.lo_minimal);
558			compareseq (part.xmid, xlim, part.ymid, ylim, part.hi_minimal);
559			}
560			}
561			}
562
563
564			/* NAME
565			fstrcmp - fuzzy string compare
566
567			SYNOPSIS
568			double fstrcmp(const CHAR s1, int l1, const CHAR s2, int l2, double);
569
570			DESCRIPTION
571			The fstrcmp function may be used to compare two string for
572			similarity. It is very useful in reducing "cascade" or
573			"secondary" errors in compilers or other situations where
574			symbol tables occur.
575
576			RETURNS
577			double; 0 if the strings are entirly dissimilar, 1 if the
578			strings are identical, and a number in between if they are
579			similar. */
580
581			double
582			fstrcmp (const CHAR *string1, int length1,
583			const CHAR *string2, int length2,
584			double minimum)
585			{
586			int i;
587
588			size_t fdiag_len;
589			static int *fdiag_buf;
590			static size_t fdiag_max;
591
592			/* set the info for each string. */
593			string[0].data = string1;
594			string[0].data_length = length1;
595			string[1].data = string2;
596			string[1].data_length = length2;
597
598			/* short-circuit obvious comparisons */
599			if (string[0].data_length == 0 && string[1].data_length == 0)
600			return 1.0;
601			if (string[0].data_length == 0 \|\| string[1].data_length == 0)
602			return 0.0;
603
604			/* Set TOO_EXPENSIVE to be approximate square root of input size,
605			bounded below by 256. */
606			too_expensive = 1;
607			for (i = string[0].data_length + string[1].data_length; i != 0; i >>= 2)
608			too_expensive <<= 1;
609			if (too_expensive < 256)
610			too_expensive = 256;
611
612			/* Because fstrcmp is typically called multiple times, while scanning
613			symbol tables, etc, attempt to minimize the number of memory
614			allocations performed. Thus, we use a static buffer for the
615			diagonal vectors, and never free them. */
616			fdiag_len = string[0].data_length + string[1].data_length + 3;
617			if (fdiag_len > fdiag_max)
618			{
619			fdiag_max = fdiag_len;
620			fdiag_buf = realloc (fdiag_buf, fdiag_max * (2 * sizeof (int)));
621			}
622			fdiag = fdiag_buf + string[1].data_length + 1;
623			bdiag = fdiag + fdiag_len;
624
625			max_edits = 1 + (string[0].data_length + string[1].data_length) * (1. - minimum);
626
627			/* Now do the main comparison algorithm */
628			string[0].edit_count = 0;
629			string[1].edit_count = 0;
630			compareseq (0, string[0].data_length, 0, string[1].data_length, 0);
631
632			/* The result is
633			((number of chars in common) / (average length of the strings)).
634			This is admittedly biased towards finding that the strings are
635			similar, however it does produce meaningful results. */
636			return ((double)
637			(string[0].data_length + string[1].data_length - string[1].edit_count - string[0].edit_count)
638			/ (string[0].data_length + string[1].data_length));
639
640			}