--- /dev/null
+/* 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));
+}
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