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+/* Functions to make fuzzy comparisons between strings
+   Copyright (C) 1988-1989, 1992-1993, 1995, 2001-2003, 2006 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 idea is to consider two strings as similar if, when
+   transforming the first string into the second string through a
+   sequence of edits (inserts and deletes of one character each),
+   this sequence is short - or equivalently, if the ordered list
+   of characters that are untouched by these edits is long.  For a
+   good introduction to the subject, read about the "Levenshtein
+   distance" in Wikipedia.
+
+   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.
+
+   Unless the 'minimal' flag is set, this code uses the TOO_EXPENSIVE
+   heuristic, by Paul Eggert, to limit the cost to O(N**1.5 log N)
+   at the price of producing suboptimal output for large inputs with
+   many differences.
+
+   Modified to work on strings rather than files
+   by Peter Miller <pmiller@agso.gov.au>, October 1995 */
+
+#include <config.h>
+
+/* Specification.  */
+#include "fstrcmp.h"
+
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+
+#include "lock.h"
+#include "tls.h"
+#include "xalloc.h"
+
+#ifndef uintptr_t
+# define uintptr_t unsigned long
+#endif
+
+
+/*
+ * Context of comparison operation.
+ */
+struct context
+{
+  /*
+   * 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;
+  }
+  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.  */
+  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.  */
+  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.  */
+  int *bdiag;
+
+  /* Edit scripts longer than this are too expensive to compute.  */
+  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, struct context *ctxt);
+
+   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 (int xoff, int xlim, int yoff, int ylim, int minimal,
+      struct partition *part, struct context *ctxt)
+{
+  int *const fd = ctxt->fdiag;	/* Give the compiler a chance. */
+  int *const bd = ctxt->bdiag;	/* Additional help for the compiler. */
+  const char *const xv = ctxt->string[0].data;	/* Still more help for the compiler. */
+  const char *const yv = ctxt->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 && ctxt->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 >= ctxt->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,
+			struct context *ctxt);
+
+   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 (int xoff, int xlim, int yoff, int ylim, int minimal,
+	    struct context *ctxt)
+{
+  const char *const xv = ctxt->string[0].data;	/* Help the compiler.  */
+  const char *const yv = ctxt->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)
+	{
+	  ctxt->string[1].edit_count++;
+	  ++yoff;
+	}
+    }
+  else if (yoff == ylim)
+    {
+      while (xoff < xlim)
+	{
+	  ctxt->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, ctxt);
+      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)
+	    ctxt->string[1].edit_count++;
+	  else
+	    ctxt->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, ctxt);
+	  compareseq (part.xmid, xlim, part.ymid, ylim, part.hi_minimal, ctxt);
+	}
+    }
+}
+
+
+/* Because fstrcmp is typically called multiple times, attempt to minimize
+   the number of memory allocations performed.  Thus, let a call reuse the
+   memory already allocated by the previous call, if it is sufficient.
+   To make it multithread-safe, without need for a lock that protects the
+   already allocated memory, store the allocated memory per thread.  Free
+   it only when the thread exits.  */
+
+static gl_tls_key_t buffer_key;	/* TLS key for a 'int *' */
+static gl_tls_key_t bufmax_key;	/* TLS key for a 'size_t' */
+
+static void
+keys_init (void)
+{
+  gl_tls_key_init (buffer_key, free);
+  gl_tls_key_init (bufmax_key, NULL);
+  /* The per-thread initial values are NULL and 0, respectively.  */
+}
+
+/* Ensure that keys_init is called once only.  */
+gl_once_define(static, keys_init_once);
+
+
+/* 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 (const char *string1, const char *string2)
+{
+  struct context ctxt;
+  int i;
+
+  size_t fdiag_len;
+  int *buffer;
+  size_t bufmax;
+
+  /* set the info for each string.  */
+  ctxt.string[0].data = string1;
+  ctxt.string[0].data_length = strlen (string1);
+  ctxt.string[1].data = string2;
+  ctxt.string[1].data_length = strlen (string2);
+
+  /* short-circuit obvious comparisons */
+  if (ctxt.string[0].data_length == 0 && ctxt.string[1].data_length == 0)
+    return 1.0;
+  if (ctxt.string[0].data_length == 0 || ctxt.string[1].data_length == 0)
+    return 0.0;
+
+  /* Set TOO_EXPENSIVE to be approximate square root of input size,
+     bounded below by 256.  */
+  ctxt.too_expensive = 1;
+  for (i = ctxt.string[0].data_length + ctxt.string[1].data_length;
+       i != 0;
+       i >>= 2)
+    ctxt.too_expensive <<= 1;
+  if (ctxt.too_expensive < 256)
+    ctxt.too_expensive = 256;
+
+  /* Allocate memory for fdiag and bdiag from a thread-local pool.  */
+  fdiag_len = ctxt.string[0].data_length + ctxt.string[1].data_length + 3;
+  gl_once (keys_init_once, keys_init);
+  buffer = (int *) gl_tls_get (buffer_key);
+  bufmax = (size_t) (uintptr_t) gl_tls_get (bufmax_key);
+  if (fdiag_len > bufmax)
+    {
+      /* Need more memory.  */
+      bufmax = 2 * bufmax;
+      if (fdiag_len > bufmax)
+	bufmax = fdiag_len;
+      /* Calling xrealloc would be a waste: buffer's contents does not need
+	 to be preserved.  */
+      if (buffer != NULL)
+	free (buffer);
+      buffer = (int *) xmalloc (bufmax * (2 * sizeof (int)));
+      gl_tls_set (buffer_key, buffer);
+      gl_tls_set (bufmax_key, (void *) (uintptr_t) bufmax);
+    }
+  ctxt.fdiag = buffer + ctxt.string[1].data_length + 1;
+  ctxt.bdiag = ctxt.fdiag + fdiag_len;
+
+  /* Now do the main comparison algorithm */
+  ctxt.string[0].edit_count = 0;
+  ctxt.string[1].edit_count = 0;
+  compareseq (0, ctxt.string[0].data_length, 0, ctxt.string[1].data_length, 0,
+	      &ctxt);
+
+  /* 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) (ctxt.string[0].data_length + ctxt.string[1].data_length
+		    - ctxt.string[1].edit_count - ctxt.string[0].edit_count)
+	  / (ctxt.string[0].data_length + ctxt.string[1].data_length));
+}