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d4a7728dc

Matheus Izvekov

2010-01-18

FAILED Duration: 35s

Subject

diff: rewrite. much smaller and more correct

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Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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editors/Config.in +0 -16 editors/diff.c +709 -1131 testsuite/diff.tests +0 -3

editors/Config.in+0 -16

@@ -35,14 +35,6 @@ config DIFF
	differences between them in a form that can be given to
	the patch command.

-	config FEATURE_DIFF_BINARY
-	bool "Enable checks for binary files"
-	default y
-	depends on DIFF
-	help
-	This option enables support for checking for binary files
-	before a comparison is carried out.
-
	config FEATURE_DIFF_DIR
	bool "Enable directory support"
	default y
@@ -51,14 +43,6 @@ config FEATURE_DIFF_DIR
	This option enables support for directory and subdirectory
	comparison.

-	config FEATURE_DIFF_MINIMAL
-	bool "Enable -d option to find smaller sets of changes"
-	default n
-	depends on DIFF
-	help
-	Enabling this option allows the use of -d to make diff
-	try hard to find the smallest possible set of changes.
-
	config ED
	bool "ed"
	default n

editors/diff.c+709 -1131

@@ -2,6 +2,7 @@
	/*
	* Mini diff implementation for busybox, adapted from OpenBSD diff.
	*
+	* Copyright (C) 2010 by Matheus Izvekov <[email protected]>
	* Copyright (C) 2006 by Robert Sullivan <[email protected]>
	* Copyright (c) 2003 Todd C. Miller <[email protected]>
	*
@@ -12,386 +13,310 @@
	* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
	*/

-	#include "libbb.h"
-
-	#define dbg_error_msg(...) ((void)0)
-	//#define dbg_error_msg(...) bb_error_msg(__VA_ARGS__)
-
-	// #define FSIZE_MAX 32768
-
-	/* NOINLINEs added to prevent gcc from merging too much into diffreg()
-	* (it bites more than it can (efficiently) chew). */
-
-	/*
-	* Output flags
-	*/
-	enum {
-	/* Print a header/footer between files */
-	/* D_HEADER = 1, - unused */
-	/* Treat file as empty (/dev/null) */
-	D_EMPTY1 = 2 * ENABLE_FEATURE_DIFF_DIR,
-	D_EMPTY2 = 4 * ENABLE_FEATURE_DIFF_DIR,
-	};
-
	/*
-	* Status values for print_status() and diffreg() return values
-	* Guide:
-	* D_SAME - files are the same
-	* D_DIFFER - files differ
-	* D_BINARY - binary files differ
-	* D_COMMON - subdirectory common to both dirs
-	* D_ONLY - file only exists in one dir
-	* D_ISDIR1 - path1 a dir, path2 a file
-	* D_ISDIR2 - path1 a file, path2 a dir
-	* D_ERROR - error occurred
-	* D_SKIPPED1 - skipped path1 as it is a special file
-	* D_SKIPPED2 - skipped path2 as it is a special file
+	* The following code uses an algorithm due to Harold Stone,
+	* which finds a pair of longest identical subsequences in
+	* the two files.
+	*
+	* The major goal is to generate the match vector J.
+	* J[i] is the index of the line in file1 corresponding
+	* to line i in file0. J[i] = 0 if there is no
+	* such line in file1.
+	*
+	* Lines are hashed so as to work in core. All potential
+	* matches are located by sorting the lines of each file
+	* on the hash (called "value"). In particular, this
+	* collects the equivalence classes in file1 together.
+	* Subroutine equiv replaces the value of each line in
+	* file0 by the index of the first element of its
+	* matching equivalence in (the reordered) file1.
+	* To save space equiv squeezes file1 into a single
+	* array member in which the equivalence classes
+	* are simply concatenated, except that their first
+	* members are flagged by changing sign.
+	*
+	* Next the indices that point into member are unsorted into
+	* array class according to the original order of file0.
+	*
+	* The cleverness lies in routine stone. This marches
+	* through the lines of file0, developing a vector klist
+	* of "k-candidates". At step i a k-candidate is a matched
+	* pair of lines x,y (x in file0, y in file1) such that
+	* there is a common subsequence of length k
+	* between the first i lines of file0 and the first y
+	* lines of file1, but there is no such subsequence for
+	* any smaller y. x is the earliest possible mate to y
+	* that occurs in such a subsequence.
+	*
+	* Whenever any of the members of the equivalence class of
+	* lines in file1 matable to a line in file0 has serial number
+	* less than the y of some k-candidate, that k-candidate
+	* with the smallest such y is replaced. The new
+	* k-candidate is chained (via pred) to the current
+	* k-1 candidate so that the actual subsequence can
+	* be recovered. When a member has serial number greater
+	* that the y of all k-candidates, the klist is extended.
+	* At the end, the longest subsequence is pulled out
+	* and placed in the array J by unravel
+	*
+	* With J in hand, the matches there recorded are
+	* checked against reality to assure that no spurious
+	* matches have crept in due to hashing. If they have,
+	* they are broken, and "jackpot" is recorded--a harmless
+	* matter except that a true match for a spuriously
+	* mated line may now be unnecessarily reported as a change.
+	*
+	* Much of the complexity of the program comes simply
+	* from trying to minimize core utilization and
+	* maximize the range of doable problems by dynamically
+	* allocating what is needed and reusing what is not.
+	* The core requirements for problems larger than somewhat
+	* are (in words) 2*length(file0) + length(file1) +
+	* 3*(number of k-candidates installed), typically about
+	* 6n words for files of length n.
	*/
-	#define D_SAME 0
-	#define D_DIFFER (1 << 0)
-	#define D_BINARY (1 << 1)
-	#define D_COMMON (1 << 2)
-	/#define D_ONLY (1 << 3) - unused /
-	#define D_ISDIR1 (1 << 4)
-	#define D_ISDIR2 (1 << 5)
-	#define D_ERROR (1 << 6)
-	#define D_SKIPPED1 (1 << 7)
-	#define D_SKIPPED2 (1 << 8)
-
-	/* Command line options */
-	#define FLAG_a (1 << 0)
-	#define FLAG_b (1 << 1)
-	#define FLAG_d (1 << 2)
-	#define FLAG_i (1 << 3)
-	#define FLAG_L (1 << 4)
-	#define FLAG_N (1 << 5)
-	#define FLAG_q (1 << 6)
-	#define FLAG_r (1 << 7)
-	#define FLAG_s (1 << 8)
-	#define FLAG_S (1 << 9)
-	#define FLAG_t (1 << 10)
-	#define FLAG_T (1 << 11)
-	#define FLAG_U (1 << 12)
-	#define FLAG_w (1 << 13)

+	#include "libbb.h"

-	struct cand {
-	int x;
-	int y;
-	int pred;
-	};
+	#if 0
+	//#define dbg_error_msg(...) bb_error_msg(__VA_ARGS__)
+	#else
+	#define dbg_error_msg(...) ((void)0)
+	#endif

-	struct line {
-	int serial;
-	int value;
+	enum { /* print_status() and diffreg() return values */
+	STATUS_SAME, /* files are the same */
+	STATUS_DIFFER, /* files differ */
+	STATUS_BINARY, /* binary files differ */
	};

-	/*
-	* The following struct is used to record change information
-	* doing a "context" or "unified" diff. (see routine "change" to
-	* understand the highly mnemonic field names)
-	*/
-	struct context_vec {
-	int a; /* start line in old file */
-	int b; /* end line in old file */
-	int c; /* start line in new file */
-	int d; /* end line in new file */
+	enum { /* Commandline flags */
+	FLAG_a,
+	FLAG_b,
+	FLAG_d,
+	FLAG_i, /* unused */
+	FLAG_L, /* unused */
+	FLAG_N,
+	FLAG_q,
+	FLAG_r,
+	FLAG_s,
+	FLAG_S, /* unused */
+	FLAG_t,
+	FLAG_T,
+	FLAG_U, /* unused */
+	FLAG_w,
	};
+	#define FLAG(x) (1 << FLAG_##x)

-
-	#define g_read_buf bb_common_bufsiz1
+	/* We cache file position to avoid excessive seeking */
+	typedef struct FILE_and_pos_t {
+	FILE *ft_fp;
+	off_t ft_pos;
+	} FILE_and_pos_t;

	struct globals {
-	bool anychange;
	smallint exit_status;
	int opt_U_context;
-	int context_idx;
-	IF_FEATURE_DIFF_DIR(int dl_count;)
-	IF_FEATURE_DIFF_DIR(char **dl;)
-	char *opt_S_start;
-	const char *label1;
-	const char *label2;
-	int J; / will be overlaid on class */
-	int clen;
-	int pref, suff; /* length of prefix and suffix */
-	int nlen[2];
-	int slen[2];
-	int clistlen; /* the length of clist */
-	struct cand clist; / merely a free storage pot for candidates */
-	long ixnew; / will be overlaid on nfile[1] */
-	long ixold; / will be overlaid on klist */
-	struct line *nfile[2];
-	struct line sfile[2]; / shortened by pruning common prefix/suffix */
-	struct context_vec *context_vector;
-	char tempname1, tempname2;
-	struct stat stb1, stb2;
+	char *label[2];
+	struct stat stb[2];
	};
	#define G (*ptr_to_globals)
-	#define anychange (G.anychange )
	#define exit_status (G.exit_status )
	#define opt_U_context (G.opt_U_context )
-	#define context_idx (G.context_idx )
-	#define dl_count (G.dl_count )
-	#define dl (G.dl )
-	#define opt_S_start (G.opt_S_start )
-	#define label1 (G.label1 )
-	#define label2 (G.label2 )
-	#define J (G.J )
-	#define clen (G.clen )
-	#define pref (G.pref )
-	#define suff (G.suff )
-	#define nlen (G.nlen )
-	#define slen (G.slen )
-	#define clistlen (G.clistlen )
-	#define clist (G.clist )
-	#define ixnew (G.ixnew )
-	#define ixold (G.ixold )
-	#define nfile (G.nfile )
-	#define sfile (G.sfile )
-	#define context_vector (G.context_vector )
-	#define stb1 (G.stb1 )
-	#define stb2 (G.stb2 )
-	#define tempname1 (G.tempname1 )
-	#define tempname2 (G.tempname2 )
+	#define label (G.label )
+	#define stb (G.stb )
	#define INIT_G() do { \
	SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
	opt_U_context = 3; \
-	context_vector = xrealloc_vector(context_vector, 6, 0); \
	} while (0)

+	typedef int token_t;

-	#if ENABLE_FEATURE_DIFF_DIR
-	static void print_only(const char path, const char entry)
-	{
-	printf("Only in %s: %s\n", path, entry);
-	}
-	#endif
+	enum {
+	/* Public */
+	TOK_EMPTY = 1 << 9, /* Line fully processed, you can proceed to the next */
+	TOK_EOF = 1 << 10, /* File ended */
+	/* Private (Only to be used by read_token() */
+	TOK_EOL = 1 << 11, /* we saw EOL (sticky) */
+	TOK_SPACE = 1 << 12, /* used -b code, means we are skipping spaces */
+	SHIFT_EOF = (sizeof(token_t)*8 - 8) - 1,
+	CHAR_MASK = 0x1ff, /* 8th bit is used to distinguish EOF from 0xff */
+	};

+	/* Restores full EOF from one 8th bit: */
+	//#define TOK2CHAR(t) (((t) << SHIFT_EOF) >> SHIFT_EOF)
+	/* We don't really need the above, we only need to have EOF != any_real_char: */
+	#define TOK2CHAR(t) ((t) & CHAR_MASK)

-	static void print_status(int val, char _path1, char _path2)
+	static void seek_ft(FILE_and_pos_t *ft, off_t pos)
	{
-	/const char const _entry = entry ? entry : "";*/
-	/char const _path1 = entry ? concat_path_file(path1, _entry) : path1;*/
-	/char const _path2 = entry ? concat_path_file(path2, _entry) : path2;*/
-
-	switch (val) {
-	/* case D_ONLY:
-	print_only(path1, entry);
-	break;
-	*/
-	case D_COMMON:
-	printf("Common subdirectories: %s and %s\n", _path1, _path2);
-	break;
-	case D_BINARY:
-	printf("Binary files %s and %s differ\n", _path1, _path2);
-	break;
-	case D_DIFFER:
-	if (option_mask32 & FLAG_q)
-	printf("Files %s and %s differ\n", _path1, _path2);
-	break;
-	case D_SAME:
-	if (option_mask32 & FLAG_s)
-	printf("Files %s and %s are identical\n", _path1, _path2);
-	break;
-	case D_ISDIR1:
-	printf("File %s is a %s while file %s is a %s\n",
-	_path1, "directory", _path2, "regular file");
-	break;
-	case D_ISDIR2:
-	printf("File %s is a %s while file %s is a %s\n",
-	_path1, "regular file", _path2, "directory");
-	break;
-	case D_SKIPPED1:
-	printf("File %s is not a regular file or directory and was skipped\n",
-	_path1);
-	break;
-	case D_SKIPPED2:
-	printf("File %s is not a regular file or directory and was skipped\n",
-	_path2);
-	break;
-	}
-	/*
-	if (entry) {
-	free(_path1);
-	free(_path2);
+	if (ft->ft_pos != pos) {
+	ft->ft_pos = pos;
+	fseeko(ft->ft_fp, pos, SEEK_SET);
	}
-	*/
	}

-
-	/* Read line, return its nonzero hash. Return 0 if EOF.
-	*
-	* Hash function taken from Robert Sedgewick, Algorithms in C, 3d ed., p 578.
+	/* Reads tokens from given fp, handling -b and -w flags
+	* The user must reset tok every line start
	*/
-	static ALWAYS_INLINE int fiddle_sum(int sum, int t)
+	static int read_token(FILE_and_pos_t *ft, token_t tok)
	{
-	return sum * 127 + t;
-	}
-	static int readhash(FILE *fp)
-	{
-	int i, t;
-	int sum;
-
-	sum = 1;
-	i = 0;
-	if (!(option_mask32 & (FLAG_b \| FLAG_w))) {
-	while ((t = getc(fp)) != '\n') {
-	if (t == EOF) {
-	if (i == 0)
-	return 0;
-	break;
-	}
-	sum = fiddle_sum(sum, t);
-	i = 1;
-	}
-	} else {
-	int space = 0;
+	tok \|= TOK_EMPTY;
+	while (!(tok & TOK_EOL)) {
+	bool is_space;
+	int t;
+
+	t = fgetc(ft->ft_fp);
+	if (t != EOF)
+	ft->ft_pos++;
+	is_space = (t == EOF \|\| isspace(t));
+
+	/* If t == EOF (-1), set both TOK_EOF and TOK_EOL */
+	tok \|= (t & (TOK_EOF + TOK_EOL));
+	/* Only EOL? */
+	if (t == '\n')
+	tok \|= TOK_EOL;
+
+	if ((option_mask32 & FLAG(w)) && is_space)
+	continue;

-	while (1) {
-	t = getc(fp);
-	switch (t) {
-	case '\t':
-	case '\r':
-	case '\v':
-	case '\f':
-	case ' ':
-	space = 1;
-	continue;
-	default:
-	if (space && !(option_mask32 & FLAG_w)) {
-	i = 1;
-	space = 0;
-	}
-	sum = fiddle_sum(sum, t);
-	i = 1;
-	continue;
-	case EOF:
-	if (i == 0)
-	return 0;
-	/* FALLTHROUGH */
-	case '\n':
-	break;
+	/* Trim char value to low 9 bits */
+	t &= CHAR_MASK;
+
+	if (option_mask32 & FLAG(b)) {
+	/* Was prev char whitespace? */
+	if (tok & TOK_SPACE) { /* yes */
+	if (is_space) /* this one too, ignore it */
+	continue;
+	tok &= ~TOK_SPACE;
+	} else if (is_space) {
+	/* 1st whitespace char.
+	* Set TOK_SPACE and replace char by ' ' */
+	t = TOK_SPACE + ' ';
	}
-	break;
	}
+	/* Clear EMPTY */
+	tok &= ~(TOK_EMPTY + CHAR_MASK);
+	/* Assign char value (low 9 bits) and maybe set TOK_SPACE */
+	tok \|= t;
+	break;
	}
-	/*
-	* There is a remote possibility that we end up with a zero sum.
-	* Zero is used as an EOF marker, so return 1 instead.
-	*/
-	return (sum == 0 ? 1 : sum);
+	#if 0
+	bb_error_msg("fp:%p tok:%x '%c'%s%s%s%s", fp, tok, tok & 0xff
+	, tok & TOK_EOF ? " EOF" : ""
+	, tok & TOK_EOL ? " EOL" : ""
+	, tok & TOK_EMPTY ? " EMPTY" : ""
+	, tok & TOK_SPACE ? " SPACE" : ""
+	);
+	#endif
+	return tok;
	}

+	struct cand {
+	int x;
+	int y;
+	int pred;
+	};

-	/* Our diff implementation is using seek.
-	* When we meet non-seekable file, we must make a temp copy.
-	*/
-	static char make_temp(FILE f, struct stat *sb)
+	static int search(const int c, int k, int y, const struct cand list)
	{
-	char *name;
-	int fd;
-
-	if (S_ISREG(sb->st_mode) \|\| S_ISBLK(sb->st_mode))
-	return NULL;
-	name = xstrdup("/tmp/difXXXXXX");
-	fd = mkstemp(name);
-	if (fd < 0)
-	bb_perror_msg_and_die("mkstemp");
-	if (bb_copyfd_eof(fileno(f), fd) < 0) {
-	clean_up:
-	unlink(name);
-	xfunc_die(); /* error message is printed by bb_copyfd_eof */
-	}
-	fstat(fd, sb);
-	close(fd);
-	if (freopen(name, "r+", f) == NULL) {
-	bb_perror_msg("freopen");
-	goto clean_up;
-	}
-	return name;
-	}
-
+	if (list[c[k]].y < y) /* quick look for typical case */
+	return k + 1;

-	/*
-	* Check to see if the given files differ.
-	* Returns 0 if they are the same, 1 if different, and -1 on error.
-	*/
-	static NOINLINE int files_differ(FILE f1, FILE f2)
-	{
-	size_t i, j;
-
-	/* Prevent making copies for "/dev/null" (too common) */
-	/* Deal with input from pipes etc */
-	tempname1 = make_temp(f1, &stb1);
-	tempname2 = make_temp(f2, &stb2);
-	if (stb1.st_size != stb2.st_size) {
-	return 1;
-	}
-	while (1) {
-	i = fread(g_read_buf, 1, COMMON_BUFSIZE/2, f1);
-	j = fread(g_read_buf + COMMON_BUFSIZE/2, 1, COMMON_BUFSIZE/2, f2);
-	if (i != j)
-	return 1;
-	if (i == 0)
-	return (ferror(f1) \|\| ferror(f2)) ? -1 : 0;
-	if (memcmp(g_read_buf,
-	g_read_buf + COMMON_BUFSIZE/2, i) != 0)
-	return 1;
+	for (int i = 0, j = k + 1;;) {
+	const int l = (i + j) >> 1;
+	if (l > i) {
+	const int t = list[c[l]].y;
+	if (t > y)
+	j = l;
+	else if (t < y)
+	i = l;
+	else
+	return l;
+	} else
+	return l + 1;
	}
	}

-
-	static void prepare(int i, FILE fp /, off_t filesize*/)
+	static unsigned isqrt(unsigned n)
	{
-	struct line *p;
-	int h;
-	size_t j, sz;
-
-	rewind(fp);
-
-	/sz = (filesize <= FSIZE_MAX ? filesize : FSIZE_MAX) / 25;/
-	/if (sz < 100)/
-	sz = 100;
-
-	p = xmalloc((sz + 3) * sizeof(p[0]));
-	j = 0;
-	while ((h = readhash(fp)) != 0) { /* while not EOF */
-	if (j == sz) {
-	sz = sz * 3 / 2;
-	p = xrealloc(p, (sz + 3) * sizeof(p[0]));
-	}
-	p[++j].value = h;
+	unsigned x = 1;
+	while (1) {
+	const unsigned y = x;
+	x = ((n / x) + x) >> 1;
+	if (x <= (y + 1) && x >= (y - 1))
+	return x;
	}
-	nlen[i] = j;
-	nfile[i] = p;
	}

-
-	static void prune(void)
+	static void stone(const int a, int n, const int b, int *J, int pref)
	{
-	int i, j;
-
-	for (pref = 0; pref < nlen[0] && pref < nlen[1] &&
-	nfile[0][pref + 1].value == nfile[1][pref + 1].value; pref++)
-	continue;
-	for (suff = 0; suff < nlen[0] - pref && suff < nlen[1] - pref &&
-	nfile[0][nlen[0] - suff].value == nfile[1][nlen[1] - suff].value;
-	suff++)
-	continue;
-	for (j = 0; j < 2; j++) {
-	sfile[j] = nfile[j] + pref;
-	slen[j] = nlen[j] - pref - suff;
-	for (i = 0; i <= slen[j]; i++)
-	sfile[j][i].serial = i;
+	const unsigned isq = isqrt(n);
+	const unsigned bound =
+	(option_mask32 & FLAG(d)) ? UINT_MAX : MAX(256, isq);
+	int clen = 1;
+	int clistlen = 100;
+	int k = 0;
+	struct cand clist = xzalloc(clistlen sizeof(clist[0]));
+	int klist = xzalloc((n + 2) sizeof(klist[0]));
+	/clist[0] = (struct cand){0}; - xzalloc did it /
+	/klist[0] = 0; /
+
+	for (struct cand cand = {1}; cand.x <= n; cand.x++) {
+	int j = a[cand.x], oldl = 0;
+	unsigned numtries = 0;
+	if (j == 0)
+	continue;
+	cand.y = -b[j];
+	cand.pred = klist[0];
+	do {
+	int l, tc;
+	if (cand.y <= clist[cand.pred].y)
+	continue;
+	l = search(klist, k, cand.y, clist);
+	if (l != oldl + 1)
+	cand.pred = klist[l - 1];
+	if (l <= k && clist[klist[l]].y <= cand.y)
+	continue;
+	if (clen == clistlen) {
+	clistlen = clistlen * 11 / 10;
+	clist = xrealloc(clist, clistlen * sizeof(clist[0]));
+	}
+	clist[clen] = cand;
+	tc = klist[l];
+	klist[l] = clen++;
+	if (l <= k) {
+	cand.pred = tc;
+	oldl = l;
+	numtries++;
+	} else {
+	k++;
+	break;
+	}
+	} while ((cand.y = b[++j]) > 0 && numtries < bound);
	}
+	/* Unravel */
+	for (struct cand *q = clist + klist[k]; q->y; q = clist + q->pred)
+	J[q->x + pref] = q->y + pref;
+	free(klist);
+	free(clist);
	}

+	struct line {
+	/* 'serial' is not used in the begining, so we reuse it
+	* to store line offsets, thus reducing memory pressure
+	*/
+	union {
+	unsigned serial;
+	off_t offset;
+	};
+	unsigned value;
+	};

	static void equiv(struct line a, int n, struct line b, int m, int *c)
	{
-	int i, j;
+	int i = 1, j = 1;

-	i = j = 1;
	while (i <= n && j <= m) {
	if (a[i].value < b[j].value)
	a[i++].value = 0;
@@ -414,286 +339,28 @@ static void equiv(struct line a, int n, struct line b, int m, int *c)
	c[j] = -1;
	}

-
-	static int isqrt(int n)
-	{
-	int y, x;
-
-	if (n == 0)
-	return 0;
-	x = 1;
-	do {
-	y = x;
-	x = n / x;
-	x += y;
-	x /= 2;
-	} while ((x - y) > 1 \|\| (x - y) < -1);
-
-	return x;
-	}
-
-
-	static int newcand(int x, int y, int pred)
+	static void unsort(const struct line f, int l, int b)
	{
-	struct cand *q;
-
-	if (clen == clistlen) {
-	clistlen = clistlen * 11 / 10;
-	clist = xrealloc(clist, clistlen * sizeof(struct cand));
-	}
-	q = clist + clen;
-	q->x = x;
-	q->y = y;
-	q->pred = pred;
-	return clen++;
-	}
-
-
-	static int search(int *c, int k, int y)
-	{
-	int i, j, l, t;
-
-	if (clist[c[k]].y < y) /* quick look for typical case */
-	return k + 1;
-	i = 0;
-	j = k + 1;
-	while (1) {
-	l = i + j;
-	if ((l >>= 1) <= i)
-	break;
-	t = clist[c[l]].y;
-	if (t > y)
-	j = l;
-	else if (t < y)
-	i = l;
-	else
-	return l;
-	}
-	return l + 1;
-	}
-
-
-	static int stone(int a, int n, int b, int *c)
-	{
-	int i, k, y, j, l;
-	int oldc, tc, oldl;
-	unsigned numtries;
-	int isq = isqrt(n);
-	#if ENABLE_FEATURE_DIFF_MINIMAL
-	const unsigned bound =
-	(option_mask32 & FLAG_d) ? UINT_MAX : MAX(256, isq);
-	#else
-	const unsigned bound = MAX(256, isq);
-	#endif
-
-	k = 0;
-	c[0] = newcand(0, 0, 0);
-	for (i = 1; i <= n; i++) {
-	j = a[i];
-	if (j == 0)
-	continue;
-	y = -b[j];
-	oldl = 0;
-	oldc = c[0];
-	numtries = 0;
-	do {
-	if (y <= clist[oldc].y)
-	continue;
-	l = search(c, k, y);
-	if (l != oldl + 1)
-	oldc = c[l - 1];
-	if (l <= k) {
-	if (clist[c[l]].y <= y)
-	continue;
-	tc = c[l];
-	c[l] = newcand(i, y, oldc);
-	oldc = tc;
-	oldl = l;
-	numtries++;
-	} else {
-	c[l] = newcand(i, y, oldc);
-	k++;
-	break;
-	}
-	} while ((y = b[++j]) > 0 && numtries < bound);
-	}
-	return k;
-	}
-
-
-	static void unravel(int p)
-	{
-	struct cand *q;
-	int i;
-
-	for (i = 0; i <= nlen[0]; i++)
-	J[i] = i <= pref ? i : i > nlen[0] - suff ? i + nlen[1] - nlen[0] : 0;
-	for (q = clist + p; q->y != 0; q = clist + q->pred)
-	J[q->x + pref] = q->y + pref;
-	}
-
-
-	static void unsort(struct line f, int l, int b)
-	{
-	int *a, i;
-
-	a = xmalloc((l + 1) * sizeof(int));
-	for (i = 1; i <= l; i++)
+	int a = xmalloc((l + 1) sizeof(a[0]));
+	for (int i = 1; i <= l; i++)
	a[f[i].serial] = f[i].value;
-	for (i = 1; i <= l; i++)
+	for (int i = 1; i <= l; i++)
	b[i] = a[i];
	free(a);
	}

-
-	static int skipline(FILE *f)
-	{
-	int i, c;
-
-	for (i = 1; (c = getc(f)) != '\n' && c != EOF; i++)
-	continue;
-	return i;
-	}
-
-
-	/*
-	* Check does double duty:
-	* 1. ferret out any fortuitous correspondences due
-	* to confounding by hashing (which result in "jackpot")
-	* 2. collect random access indexes to the two files
-	*/
-	static NOINLINE void check(FILE f1, FILE f2)
-	{
-	int i, j, jackpot, c, d;
-	long ctold, ctnew;
-
-	rewind(f1);
-	rewind(f2);
-	j = 1;
-	ixold[0] = ixnew[0] = 0;
-	jackpot = 0;
-	ctold = ctnew = 0;
-	for (i = 1; i <= nlen[0]; i++) {
-	if (J[i] == 0) {
-	ixold[i] = ctold += skipline(f1);
-	continue;
-	}
-	while (j < J[i]) {
-	ixnew[j] = ctnew += skipline(f2);
-	j++;
-	}
-	if (option_mask32 & (FLAG_b \| FLAG_w \| FLAG_i)) {
-	while (1) {
-	c = getc(f1);
-	d = getc(f2);
-	/*
-	* GNU diff ignores a missing newline
-	* in one file if bflag \|\| wflag.
-	*/
-	if ((option_mask32 & (FLAG_b \| FLAG_w))
-	&& ((c == EOF && d == '\n') \|\| (c == '\n' && d == EOF))
-	) {
-	break;
-	}
-	ctold++;
-	ctnew++;
-	if ((option_mask32 & FLAG_b) && isspace(c) && isspace(d)) {
-	do {
-	if (c == '\n')
-	break;
-	ctold++;
-	c = getc(f1);
-	} while (isspace(c));
-	do {
-	if (d == '\n')
-	break;
-	ctnew++;
-	d = getc(f2);
-	} while (isspace(d));
-	} else if (option_mask32 & FLAG_w) {
-	while (isspace(c) && c != '\n') {
-	c = getc(f1);
-	ctold++;
-	}
-	while (isspace(d) && d != '\n') {
-	d = getc(f2);
-	ctnew++;
-	}
-	}
-	if (c != d) {
-	jackpot++;
-	J[i] = 0;
-	if (c != '\n' && c != EOF)
-	ctold += skipline(f1);
-	if (d != '\n' && c != EOF)
-	ctnew += skipline(f2);
-	break;
-	}
-	if (c == '\n' \|\| c == EOF)
-	break;
-	}
-	} else {
-	while (1) {
-	ctold++;
-	ctnew++;
-	c = getc(f1);
-	d = getc(f2);
-	if (c != d) {
-	J[i] = 0;
-	if (c != '\n' && c != EOF)
-	ctold += skipline(f1);
-	/* was buggy? "if (d != '\n' && c != EOF)" */
-	if (d != '\n' && d != EOF)
-	ctnew += skipline(f2);
-	break;
-	}
-	if (c == '\n' \|\| c == EOF)
-	break;
-	}
-	}
-	ixold[i] = ctold;
-	ixnew[j] = ctnew;
-	j++;
-	}
-	for (; j <= nlen[1]; j++)
-	ixnew[j] = ctnew += skipline(f2);
-	}
-
-
-	/* shellsort CACM #201 */
-	static void sort(struct line *a, int n)
+	static int line_compar(const void a, const void b)
	{
-	struct line ai, aim, w;
-	int j, m = 0, k;
-
-	if (n == 0)
-	return;
-	for (j = 1; j <= n; j *= 2)
-	m = 2 * j - 1;
-	for (m /= 2; m != 0; m /= 2) {
-	k = n - m;
-	for (j = 1; j <= k; j++) {
-	for (ai = &a[j]; ai > a; ai -= m) {
-	aim = &ai[m];
-	if (aim < ai)
-	break; /* wraparound */
-	if (aim->value > ai[0].value
-	\|\| (aim->value == ai[0].value && aim->serial > ai[0].serial)
-	) {
-	break;
-	}
-	w.value = ai[0].value;
-	ai[0].value = aim->value;
-	aim->value = w.value;
-	w.serial = ai[0].serial;
-	ai[0].serial = aim->serial;
-	aim->serial = w.serial;
-	}
-	}
-	}
+	#define l0 ((const struct line*)a)
+	#define l1 ((const struct line*)b)
+	int r = l0->value - l1->value;
+	if (r)
+	return r;
+	return l0->serial - l1->serial;
+	#undef l0
+	#undef l1
	}

-
	static void uni_range(int a, int b)
	{
	if (a < b)
@@ -704,33 +371,23 @@ static void uni_range(int a, int b)
	printf("%d,0", b);
	}

-
-	static void fetch(long f, int a, int b, FILE lb, int ch)
+	static void fetch(FILE_and_pos_t ft, const off_t ix, int a, int b, int ch)
	{
-	int i, j, c, lastc, col, nc;
-
-	if (a > b)
-	return;
-	for (i = a; i <= b; i++) {
-	fseek(lb, f[i - 1], SEEK_SET);
-	nc = f[i] - f[i - 1];
-	if (ch != '\0') {
-	putchar(ch);
-	if (option_mask32 & FLAG_T)
-	putchar('\t');
-	}
-	col = 0;
-	for (j = 0, lastc = '\0'; j < nc; j++, lastc = c) {
-	c = getc(lb);
+	for (int i = a; i <= b; i++) {
+	seek_ft(ft, ix[i - 1]);
+	putchar(ch);
+	if (option_mask32 & FLAG(T))
+	putchar('\t');
+	for (int j = 0, col = 0; j < ix[i] - ix[i - 1]; j++) {
+	int c = fgetc(ft->ft_fp);
	if (c == EOF) {
	printf("\n\\ No newline at end of file\n");
	return;
	}
-	if (c == '\t' && (option_mask32 & FLAG_t)) {
-	do {
-	putchar(' ');
-	} while (++col & 7);
-	} else {
+	ft->ft_pos++;
+	if (c == '\t' && (option_mask32 & FLAG(t)))
+	do putchar(' '); while (++col & 7);
+	else {
	putchar(c);
	col++;
	}
@@ -738,540 +395,477 @@ static void fetch(long f, int a, int b, FILE lb, int ch)
	}
	}

-
-	#if ENABLE_FEATURE_DIFF_BINARY
-	static int asciifile(FILE *f)
+	/* Creates the match vector J, where J[i] is the index
+	* of the line in the new file corresponding to the line i
+	* in the old file. Lines start at 1 instead of 0, that value
+	* being used instead to denote no corresponding line.
+	* This vector is dynamically allocated and must be freed by the caller.
+	*
+	* * fp is an input parameter, where fp[0] and fp[1] are the open
+	* old file and new file respectively.
+	* * nlen is an output variable, where nlen[0] and nlen[1]
+	* gets the number of lines in the old and new file respectively.
+	* * ix is an output variable, where ix[0] and ix[1] gets
+	* assigned dynamically allocated vectors of the offsets of the lines
+	* of the old and new file respectively. These must be freed by the caller.
+	*/
+	static int create_J(FILE_and_pos_t ft[2], int nlen[2], off_t ix[2])
	{
-	int i, cnt;
-
-	if (option_mask32 & FLAG_a)
-	return 1;
-	rewind(f);
-	cnt = fread(g_read_buf, 1, COMMON_BUFSIZE, f);
-	for (i = 0; i < cnt; i++) {
-	if (!isprint_asciionly(g_read_buf[i])
-	&& !isspace(g_read_buf[i])
-	) {
-	return 0;
+	int J, slen[2], class, *member;
+	struct line nfile[2], sfile[2];
+	int pref = 0, suff = 0;
+
+	/* Lines of both files are hashed, and in the process
+	* their offsets are stored in the array ix[fileno]
+	* where fileno == 0 points to the old file, and
+	* fileno == 1 points to the new one.
+	*/
+	for (int i = 0; i < 2; i++) {
+	unsigned hash;
+	token_t tok;
+	size_t sz = 100;
+	nfile[i] = xmalloc((sz + 3) * sizeof(nfile[i][0]));
+	seek_ft(&ft[i], 0);
+
+	nlen[i] = 0;
+	/* We could zalloc nfile, but then zalloc starts showing in gprof at ~1% */
+	nfile[i][0].offset = 0;
+	goto start; /* saves code */
+	while (1) {
+	tok = read_token(&ft[i], tok);
+	if (!(tok & TOK_EMPTY)) {
+	/* Hash algorithm taken from Robert Sedgewick, Algorithms in C, 3d ed., p 578. */
+	hash = hash * 128 - hash + TOK2CHAR(tok);
+	continue;
+	}
+	if (nlen[i]++ == sz) {
+	sz = sz * 3 / 2;
+	nfile[i] = xrealloc(nfile[i], (sz + 3) * sizeof(nfile[i][0]));
+	}
+	/* line_compar needs hashes fit into positive int */
+	nfile[i][nlen[i]].value = hash & INT_MAX;
+	/* like ftello(ft[i].ft_fp) but faster (avoids lseek syscall) */
+	nfile[i][nlen[i]].offset = ft[i].ft_pos;
+	if (tok & TOK_EOF) {
+	/* EOF counts as a token, so we have to adjust it here */
+	nfile[i][nlen[i]].offset++;
+	break;
+	}
+	start:
+	hash = tok = 0;
	}
+	/* Exclude lone EOF line from the end of the file, to make fetch()'s job easier */
+	if (nfile[i][nlen[i]].offset - nfile[i][nlen[i] - 1].offset == 1)
+	nlen[i]--;
+	/* Now we copy the line offsets into ix */
+	ix[i] = xmalloc((nlen[i] + 2) * sizeof(ix[i][0]));
+	for (int j = 0; j < nlen[i] + 1; j++)
+	ix[i][j] = nfile[i][j].offset;
+	}
+
+	/* lenght of prefix and suffix is calculated */
+	for (; pref < nlen[0] && pref < nlen[1] &&
+	nfile[0][pref + 1].value == nfile[1][pref + 1].value;
+	pref++);
+	for (; suff < nlen[0] - pref && suff < nlen[1] - pref &&
+	nfile[0][nlen[0] - suff].value == nfile[1][nlen[1] - suff].value;
+	suff++);
+	/* Arrays are pruned by the suffix and prefix lenght,
+	* the result being sorted and stored in sfile[fileno],
+	* and their sizes are stored in slen[fileno]
+	*/
+	for (int j = 0; j < 2; j++) {
+	sfile[j] = nfile[j] + pref;
+	slen[j] = nlen[j] - pref - suff;
+	for (int i = 0; i <= slen[j]; i++)
+	sfile[j][i].serial = i;
+	qsort(sfile[j] + 1, slen[j], sizeof(*sfile[j]), line_compar);
	}
-	return 1;
-	}
-	#else
-	#define asciifile(f) 1
-	#endif
-
-
-	/* dump accumulated "unified" diff changes */
-	static void dump_unified_vec(FILE f1, FILE f2)
-	{
-	struct context_vec *cvp = context_vector;
-	int lowa, upb, lowc, upd;
-	int a, b, c, d;
-	char ch;
-
-	if (context_idx < 0)
-	return;
-
-	dbg_error_msg("dumping %d context_vecs", context_idx+1);
-
-	b = d = 0; /* gcc */
-	lowa = MAX(1, cvp->a - opt_U_context);
-	upb = MIN(nlen[0], context_vector[context_idx].b + opt_U_context);
-	lowc = MAX(1, cvp->c - opt_U_context);
-	upd = MIN(nlen[1], context_vector[context_idx].d + opt_U_context);
-
-	printf("@@ -");
-	uni_range(lowa, upb);
-	printf(" +");
-	uni_range(lowc, upd);
-	printf(" @@\n");
-
-	/*
-	* Output changes in "unified" diff format--the old and new lines
-	* are printed together.
+	/* nfile arrays are reused to reduce memory pressure
+	* The #if zeroed out section performs the same task as the
+	* one in the #else section.
+	* Peak memory usage is higher, but one array copy is avoided
+	* by not using unsort()
	*/
-	for (; cvp <= &context_vector[context_idx]; cvp++) {
-	a = cvp->a;
-	b = cvp->b;
-	c = cvp->c;
-	d = cvp->d;
-
-	/*
-	* c: both new and old changes
-	* d: only changes in the old file
-	* a: only changes in the new file
-	*/
-	if (a <= b && c <= d)
-	ch = 'c';
-	else
-	ch = (a <= b) ? 'd' : 'a';
	#if 0
-	switch (ch) {
-	case 'c':
-	// fetch() seeks!
-	fetch(ixold, lowa, a - 1, f1, ' ');
-	fetch(ixold, a, b, f1, '-');
-	fetch(ixnew, c, d, f2, '+');
-	break;
-	case 'd':
-	fetch(ixold, lowa, a - 1, f1, ' ');
-	fetch(ixold, a, b, f1, '-');
-	break;
-	case 'a':
-	fetch(ixnew, lowc, c - 1, f2, ' ');
-	fetch(ixnew, c, d, f2, '+');
-	break;
-	}
+	member = xmalloc((slen[1] + 2) * sizeof(member[0]));
+	equiv(sfile[0], slen[0], sfile[1], slen[1], member);
+	free(nfile[1]);
+
+	class = xmalloc((slen[0] + 1) * sizeof(class[0]));
+	for (int i = 1; i <= slen[0]; i++) /* Unsorting */
+	class[sfile[0][i].serial] = sfile[0][i].value;
+	free(nfile[0]);
	#else
-	if (ch == 'c' \|\| ch == 'd') {
-	fetch(ixold, lowa, a - 1, f1, ' ');
-	fetch(ixold, a, b, f1, '-');
-	}
-	if (ch == 'a')
-	fetch(ixnew, lowc, c - 1, f2, ' ');
-	if (ch == 'c' \|\| ch == 'a')
-	fetch(ixnew, c, d, f2, '+');
-	#endif
-	lowa = b + 1;
-	lowc = d + 1;
-	}
-	fetch(ixnew, d + 1, upd, f2, ' ');
+	member = (int *)nfile[1];
+	equiv(sfile[0], slen[0], sfile[1], slen[1], member);
+	member = xrealloc(member, (slen[1] + 2) * sizeof(member[0]));

-	context_idx = -1;
-	}
+	class = (int *)nfile[0];
+	unsort(sfile[0], slen[0], (int *)nfile[0]);
+	class = xrealloc(class, (slen[0] + 2) * sizeof(class[0]));
+	#endif
+	J = xmalloc((nlen[0] + 2) * sizeof(J[0]));
+	/* The elements of J which fall inside the prefix and suffix regions
+	* are marked as unchanged, while the ones which fall outside
+	* are initialized with 0 (no matches), so that function stone can
+	* then assign them their right values
+	*/
+	for (int i = 0, delta = nlen[1] - nlen[0]; i <= nlen[0]; i++)
+	J[i] = i <= pref ? i :
+	i > (nlen[0] - suff) ? (i + delta) : 0;
+	/* Here the magic is performed */
+	stone(class, slen[0], member, J, pref);
+	J[nlen[0] + 1] = nlen[1] + 1;

+	free(class);
+	free(member);

-	static void print_header(const char file1, const char file2)
-	{
-	if (label1)
-	printf("--- %s\n", label1);
-	else
-	printf("--- %s\t%s", file1, ctime(&stb1.st_mtime));
-	if (label2)
-	printf("+++ %s\n", label2);
-	else
-	printf("+++ %s\t%s", file2, ctime(&stb2.st_mtime));
-	}
+	/* Both files are rescanned, in an effort to find any lines
+	* which, due to limitations intrinsic to any hashing algorithm,
+	* are different but ended up confounded as the same
+	*/
+	for (int i = 1; i <= nlen[0]; i++) {
+	if (!J[i])
+	continue;

+	seek_ft(&ft[0], ix[0][i - 1]);
+	seek_ft(&ft[1], ix[1][J[i] - 1]);

-	/*
-	* Indicate that there is a difference between lines a and b of the from file
-	* to get to lines c to d of the to file. If a is greater than b then there
-	* are no lines in the from file involved and this means that there were
-	* lines appended (beginning at b). If c is greater than d then there are
-	* lines missing from the to file.
-	*/
-	static void change(const char file1, FILE f1, const char file2, FILE f2,
-	int a, int b, int c, int d)
-	{
-	if ((a > b && c > d) \|\| (option_mask32 & FLAG_q)) {
-	//compat BUG: "diff -ub F1 F2" will output nothing, but will exit 1
-	//if F1 and F2 differ only in whitespace. "standard" diff exits 0.
-	//This is the place where this erroneous exitcode is set:
-	dbg_error_msg("%d: abcd:%d,%d,%d,%d, anychange=1", __LINE__, a,b,c,d);
-	anychange = 1;
-	return;
-	}
+	for (int j = J[i]; i <= nlen[0] && J[i] == j; i++, j++) {
+	token_t tok0 = 0, tok1 = 0;
+	do {
+	tok0 = read_token(&ft[0], tok0);
+	tok1 = read_token(&ft[1], tok1);

-	if (anychange == 0) {
-	/*
-	* Print the context/unidiff header first time through.
-	*/
-	print_header(file1, file2);
-	} else if (a > context_vector[context_idx].b + (2 * opt_U_context) + 1
-	&& c > context_vector[context_idx].d + (2 * opt_U_context) + 1
-	) {
-	/*
-	* If this change is more than 'context' lines from the
-	* previous change, dump the record and reset it.
-	*/
-	// dump_unified_vec() seeks!
-	dump_unified_vec(f1, f2);
+	if (((tok0 ^ tok1) & TOK_EMPTY) != 0 /* one is empty (not both) */
+	\|\| (!(tok0 & TOK_EMPTY) && TOK2CHAR(tok0) != TOK2CHAR(tok1)))
+	J[i] = 0; /* Break the correspondence */
+	} while (!(tok0 & tok1 & TOK_EMPTY));
+	}
	}
-	context_idx++;
-	context_vector = xrealloc_vector(context_vector, 6, context_idx);
-	context_vector[context_idx].a = a;
-	context_vector[context_idx].b = b;
-	context_vector[context_idx].c = c;
-	context_vector[context_idx].d = d;
-	dbg_error_msg("new context_vec[%d]:%d,%d,%d,%d", context_idx, a,b,c,d);
-	anychange = 1;
-	}

-
-	static void output(const char file1, FILE f1, const char file2, FILE f2)
-	{
-	/* Note that j0 and j1 can't be used as they are defined in math.h.
-	* This also allows the rather amusing variable 'j00'... */
-	int m, i0, i1, j00, j01;
-
-	rewind(f1);
-	rewind(f2);
-	m = nlen[0];
-	J[0] = 0;
-	J[m + 1] = nlen[1] + 1;
-	for (i0 = 1; i0 <= m; i0 = i1 + 1) {
-	while (i0 <= m && J[i0] == J[i0 - 1] + 1)
-	i0++;
-	j00 = J[i0 - 1] + 1;
-	i1 = i0 - 1;
-	while (i1 < m && J[i1 + 1] == 0)
-	i1++;
-	j01 = J[i1 + 1] - 1;
-	J[i1] = j01;
-	// change() seeks!
-	change(file1, f1, file2, f2, i0, i1, j00, j01);
-	}
-	if (m == 0) {
-	// change() seeks!
-	change(file1, f1, file2, f2, 1, 0, 1, nlen[1]);
-	}
-	if (anychange != 0 && !(option_mask32 & FLAG_q)) {
-	// dump_unified_vec() seeks!
-	dump_unified_vec(f1, f2);
-	}
+	return J;
	}

	/*
-	* The following code uses an algorithm due to Harold Stone,
-	* which finds a pair of longest identical subsequences in
-	* the two files.
-	*
-	* The major goal is to generate the match vector J.
-	* J[i] is the index of the line in file1 corresponding
-	* to line i in file0. J[i] = 0 if there is no
-	* such line in file1.
-	*
-	* Lines are hashed so as to work in core. All potential
-	* matches are located by sorting the lines of each file
-	* on the hash (called "value"). In particular, this
-	* collects the equivalence classes in file1 together.
-	* Subroutine equiv replaces the value of each line in
-	* file0 by the index of the first element of its
-	* matching equivalence in (the reordered) file1.
-	* To save space equiv squeezes file1 into a single
-	* array member in which the equivalence classes
-	* are simply concatenated, except that their first
-	* members are flagged by changing sign.
-	*
-	* Next the indices that point into member are unsorted into
-	* array class according to the original order of file0.
-	*
-	* The cleverness lies in routine stone. This marches
-	* through the lines of file0, developing a vector klist
-	* of "k-candidates". At step i a k-candidate is a matched
-	* pair of lines x,y (x in file0, y in file1) such that
-	* there is a common subsequence of length k
-	* between the first i lines of file0 and the first y
-	* lines of file1, but there is no such subsequence for
-	* any smaller y. x is the earliest possible mate to y
-	* that occurs in such a subsequence.
-	*
-	* Whenever any of the members of the equivalence class of
-	* lines in file1 matable to a line in file0 has serial number
-	* less than the y of some k-candidate, that k-candidate
-	* with the smallest such y is replaced. The new
-	* k-candidate is chained (via pred) to the current
-	* k-1 candidate so that the actual subsequence can
-	* be recovered. When a member has serial number greater
-	* that the y of all k-candidates, the klist is extended.
-	* At the end, the longest subsequence is pulled out
-	* and placed in the array J by unravel
-	*
-	* With J in hand, the matches there recorded are
-	* checked against reality to assure that no spurious
-	* matches have crept in due to hashing. If they have,
-	* they are broken, and "jackpot" is recorded--a harmless
-	* matter except that a true match for a spuriously
-	* mated line may now be unnecessarily reported as a change.
-	*
-	* Much of the complexity of the program comes simply
-	* from trying to minimize core utilization and
-	* maximize the range of doable problems by dynamically
-	* allocating what is needed and reusing what is not.
-	* The core requirements for problems larger than somewhat
-	* are (in words) 2*length(file0) + length(file1) +
-	* 3*(number of k-candidates installed), typically about
-	* 6n words for files of length n.
+	* The following struct is used to record change information
+	* doing a "context" or "unified" diff.
	*/
-	/* NB: files can be not REGular. The only sure thing that they
-	* are not both DIRectories. */
-	static unsigned diffreg(const char file1, const char file2, int flags)
+	struct context_vec {
+	int a; /* start line in old file */
+	int b; /* end line in old file */
+	int c; /* start line in new file */
+	int d; /* end line in new file */
+	};
+
+	static bool diff(FILE_and_pos_t ft[2], char *file[2])
	{
-	int member; / will be overlaid on nfile[1] */
-	int class; / will be overlaid on nfile[0] */
-	int klist; / will be overlaid on nfile[0] after class */
-	FILE *f1;
-	FILE *f2;
-	unsigned rval;
-	int i;
-
-	anychange = 0;
-	context_idx = -1;
-	tempname1 = tempname2 = NULL;
-
-	/* Is any of them a directory? Then it's simple */
-	if (S_ISDIR(stb1.st_mode) != S_ISDIR(stb2.st_mode))
-	return (S_ISDIR(stb1.st_mode) ? D_ISDIR1 : D_ISDIR2);
-
-	/* None of them are directories */
-	rval = D_SAME;
-
-	if (flags & D_EMPTY1)
-	/* can't be stdin, but xfopen_stdin() is smaller code */
-	file1 = bb_dev_null;
-	f1 = xfopen_stdin(file1);
-	if (flags & D_EMPTY2)
-	file2 = bb_dev_null;
-	f2 = xfopen_stdin(file2);
-
-	/* NB: if D_EMPTY1/2 is set, other file is always a regular file,
-	* not pipe/fifo/chardev/etc - D_EMPTY is used by "diff -r" only,
-	* and it never diffs non-ordinary files in subdirs. */
-	if (!(flags & (D_EMPTY1 \| D_EMPTY2))) {
-	/* Quick check whether they are different */
-	/* NB: copies non-REG files to tempfiles and fills tempname1/2 */
-	i = files_differ(f1, f2);
-	if (i != 1) { /* not different? */
-	if (i != 0) /* error? */
-	exit_status \|= 2;
-	goto closem;
-	}
-	}
+	int nlen[2];
+	off_t *ix[2];
+	int *J = create_J(ft, nlen, ix);

-	if (!asciifile(f1) \|\| !asciifile(f2)) {
-	rval = D_BINARY;
-	exit_status \|= 1;
-	goto closem;
-	}
+	bool anychange = false;
+	struct context_vec *vec = NULL;
+	int idx = -1, i = 1;

-	// Rewind inside!
-	prepare(0, f1 /, stb1.st_size/);
-	prepare(1, f2 /, stb2.st_size/);
-	prune();
-	sort(sfile[0], slen[0]);
-	sort(sfile[1], slen[1]);
+	do {
+	while (1) {
+	struct context_vec v;

-	member = (int *) nfile[1];
-	equiv(sfile[0], slen[0], sfile[1], slen[1], member);
-	//TODO: xrealloc_vector?
-	member = xrealloc(member, (slen[1] + 2) * sizeof(int));
-
-	class = (int *) nfile[0];
-	unsort(sfile[0], slen[0], class);
-	class = xrealloc(class, (slen[0] + 2) * sizeof(int));
-
-	klist = xmalloc((slen[0] + 2) * sizeof(int));
-	clen = 0;
-	clistlen = 100;
-	clist = xmalloc(clistlen * sizeof(struct cand));
-	i = stone(class, slen[0], member, klist);
-	free(member);
-	free(class);
+	for (v.a = i; v.a <= nlen[0] && J[v.a] == J[v.a - 1] + 1; v.a++)
+	continue;
+	v.c = J[v.a - 1] + 1;

-	J = xrealloc(J, (nlen[0] + 2) * sizeof(int));
-	unravel(klist[i]);
-	free(clist);
-	free(klist);
+	for (v.b = v.a - 1; v.b < nlen[0] && !J[v.b + 1]; v.b++)
+	continue;
+	v.d = J[v.b + 1] - 1;
+	/*
+	* Indicate that there is a difference between lines a and b of the 'from' file
+	* to get to lines c to d of the 'to' file. If a is greater than b then there
+	* are no lines in the 'from' file involved and this means that there were
+	* lines appended (beginning at b). If c is greater than d then there are
+	* lines missing from the 'to' file.
+	*/
+	if (v.a <= v.b \|\| v.c <= v.d) {
+	/*
+	* If this change is more than 'context' lines from the
+	* previous change, dump the record and reset it.
+	*/
+	if (idx >= 0
+	&& v.a > vec[idx].b + (2 * opt_U_context) + 1
+	&& v.c > vec[idx].d + (2 * opt_U_context) + 1
+	) {
+	break;
+	}
+	vec = xrealloc_vector(vec, 6, ++idx);
+	vec[idx] = v;
+	}
+
+	i = v.b + 1;
+	if (i > nlen[0])
+	break;
+	J[v.b] = v.d;
+	}
+	if (idx < 0)
+	continue;
+	if (!(option_mask32 & FLAG(q))) {
+	struct context_vec *cvp = vec;
+	int lowa = MAX(1, cvp->a - opt_U_context);
+	int upb = MIN(nlen[0], vec[idx].b + opt_U_context);
+	int lowc = MAX(1, cvp->c - opt_U_context);
+	int upd = MIN(nlen[1], vec[idx].d + opt_U_context);
+
+	if (!anychange) {
+	/* Print the context/unidiff header first time through */
+	printf("--- %s\n", label[0] ?: file[0]);
+	printf("+++ %s\n", label[1] ?: file[1]);
+	}

-	ixold = xrealloc(ixold, (nlen[0] + 2) * sizeof(long));
-	ixnew = xrealloc(ixnew, (nlen[1] + 2) * sizeof(long));
-	// Rewind inside!
-	check(f1, f2);
-	// Rewind inside!
-	output(file1, f1, file2, f2);
+	printf("@@ -");
+	uni_range(lowa, upb);
+	printf(" +");
+	uni_range(lowc, upd);
+	printf(" @@\n");

-	closem:
-	if (anychange) {
-	exit_status \|= 1;
-	dbg_error_msg("exit_status\|=1 = %d", exit_status);
-	if (rval == D_SAME)
-	rval = D_DIFFER;
-	}
-	fclose_if_not_stdin(f1);
-	fclose_if_not_stdin(f2);
-	if (tempname1) {
-	unlink(tempname1);
-	free(tempname1);
-	}
-	if (tempname2) {
-	unlink(tempname2);
-	free(tempname2);
-	}
-	return rval;
+	/*
+	* Output changes in "unified" diff format--the old and new lines
+	* are printed together.
+	*/
+	while (1) {
+	bool end = cvp > &vec[idx];
+	fetch(&ft[0], ix[0], lowa, end ? upb : cvp->a - 1, ' ');
+	if (end)
+	break;
+	fetch(&ft[0], ix[0], cvp->a, cvp->b, '-');
+	fetch(&ft[1], ix[1], cvp->c, cvp->d, '+');
+	lowa = cvp++->b + 1;
+	}
+	}
+	idx = -1;
+	anychange = true;
+	} while (i <= nlen[0]);
+
+	free(vec);
+	free(ix[0]);
+	free(ix[1]);
+	free(J);
+	return anychange;
	}

-
-	#if ENABLE_FEATURE_DIFF_DIR
-	static void do_diff(char dir1, char path1, char dir2, char path2)
+	static int diffreg(char *file[2])
	{
-	int flags = 0; /D_HEADER;/
-	int val;
-	char fullpath1 = NULL; / if -N */
-	char *fullpath2 = NULL;
-
-	if (path1)
-	fullpath1 = concat_path_file(dir1, path1);
-	if (path2)
-	fullpath2 = concat_path_file(dir2, path2);
-
-	if (!fullpath1 \|\| stat(fullpath1, &stb1) != 0) {
-	flags \|= D_EMPTY1;
-	memset(&stb1, 0, sizeof(stb1));
-	if (path2) {
-	free(fullpath1);
-	fullpath1 = concat_path_file(dir1, path2);
+	FILE_and_pos_t ft[2];
+	bool binary = false, differ = false;
+	int status = STATUS_SAME;
+
+	for (int i = 0; i < 2; i++) {
+	int fd = open_or_warn_stdin(file[i]);
+	if (fd == -1)
+	xfunc_die();
+	/* Our diff implementation is using seek.
+	* When we meet non-seekable file, we must make a temp copy.
+	*/
+	ft[i].ft_pos = 0;
+	if (lseek(fd, 0, SEEK_SET) == -1 && errno == ESPIPE) {
+	char name[] = "/tmp/difXXXXXX";
+	int fd_tmp = mkstemp(name);
+	if (fd_tmp < 0)
+	bb_perror_msg_and_die("mkstemp");
+	unlink(name);
+	ft[i].ft_pos = bb_copyfd_eof(fd, fd_tmp);
+	/* error message is printed by bb_copyfd_eof */
+	if (ft[i].ft_pos < 0)
+	xfunc_die();
+	fstat(fd, &stb[i]);
+	if (fd) /* Prevents closing of stdin */
+	close(fd);
+	fd = fd_tmp;
	}
+	ft[i].ft_fp = fdopen(fd, "r");
	}
-	if (!fullpath2 \|\| stat(fullpath2, &stb2) != 0) {
-	flags \|= D_EMPTY2;
-	memset(&stb2, 0, sizeof(stb2));
-	stb2.st_mode = stb1.st_mode;
-	if (path1) {
-	free(fullpath2);
-	fullpath2 = concat_path_file(dir2, path1);
+
+	while (1) {
+	const size_t sz = COMMON_BUFSIZE / 2;
+	char *const buf0 = bb_common_bufsiz1;
+	char *const buf1 = buf0 + sz;
+	int i, j;
+	i = fread(buf0, 1, sz, ft[0].ft_fp);
+	ft[0].ft_pos += i;
+	j = fread(buf1, 1, sz, ft[1].ft_fp);
+	ft[1].ft_pos += j;
+	if (i != j) {
+	differ = true;
+	i = MIN(i, j);
+	}
+	if (i == 0)
+	break;
+	for (int k = 0; k < i; k++) {
+	if (!buf0[k] \|\| !buf1[k])
+	binary = true;
+	if (buf0[k] != buf1[k])
+	differ = true;
	}
	}
-
-	if (stb1.st_mode == 0)
-	stb1.st_mode = stb2.st_mode;
-
-	if (S_ISDIR(stb1.st_mode) && S_ISDIR(stb2.st_mode)) {
-	printf("Common subdirectories: %s and %s\n", fullpath1, fullpath2);
-	goto ret;
+	if (differ) {
+	if (binary && !(option_mask32 & FLAG(a)))
+	status = STATUS_BINARY;
+	else if (diff(ft, file))
+	status = STATUS_DIFFER;
	}
+	if (status != STATUS_SAME)
+	exit_status \|= 1;

-	if (!S_ISREG(stb1.st_mode) && !S_ISDIR(stb1.st_mode))
-	val = D_SKIPPED1;
-	else if (!S_ISREG(stb2.st_mode) && !S_ISDIR(stb2.st_mode))
-	val = D_SKIPPED2;
-	else {
-	/* Both files are either REGular or DIRectories */
-	val = diffreg(fullpath1, fullpath2, flags);
-	}
+	fclose_if_not_stdin(ft[0].ft_fp);
+	fclose_if_not_stdin(ft[1].ft_fp);

-	print_status(val, fullpath1, fullpath2 /, NULL/);
-	ret:
-	free(fullpath1);
-	free(fullpath2);
+	return status;
	}
-	#endif

+	static void print_status(int status, char *path[2])
+	{
+	switch (status) {
+	case STATUS_BINARY:
+	case STATUS_DIFFER:
+	if ((option_mask32 & FLAG(q)) \|\| status == STATUS_BINARY)
+	printf("Files %s and %s differ\n", path[0], path[1]);
+	break;
+	case STATUS_SAME:
+	if (option_mask32 & FLAG(s))
+	printf("Files %s and %s are identical\n", path[0], path[1]);
+	break;
+	}
+	}

	#if ENABLE_FEATURE_DIFF_DIR
+	struct dlist {
+	size_t len;
+	int s, e;
+	char **dl;
+	};
+
	/* This function adds a filename to dl, the directory listing. */
	static int FAST_FUNC add_to_dirlist(const char *filename,
	struct stat *sb UNUSED_PARAM,
-	void *userdata,
-	int depth UNUSED_PARAM)
+	void *userdata, int depth UNUSED_PARAM)
	{
-	dl = xrealloc_vector(dl, 5, dl_count);
-	dl[dl_count] = xstrdup(filename + (int)(ptrdiff_t)userdata);
-	dl_count++;
+	struct dlist *const l = userdata;
+	l->dl = xrealloc_vector(l->dl, 6, l->e);
+	/* + 1 skips "/" after dirname */
+	l->dl[l->e] = xstrdup(filename + l->len + 1);
+	l->e++;
	return TRUE;
	}

-
-	/* This returns a sorted directory listing. */
-	static char *get_recursive_dirlist(char path)
+	/* If recursion is not set, this function adds the directory
+	* to the list and prevents recursive_action from recursing into it.
+	*/
+	static int FAST_FUNC skip_dir(const char *filename,
+	struct stat sb, void userdata,
+	int depth)
	{
-	dl_count = 0;
-	dl = xzalloc(sizeof(dl[0]));
-
-	/* We need to trim root directory prefix.
-	* Using void *userdata to specify its length,
-	* add_to_dirlist will remove it. */
-	if (option_mask32 & FLAG_r) {
-	recursive_action(path, ACTION_RECURSE\|ACTION_FOLLOWLINKS,
-	add_to_dirlist, /* file_action */
-	NULL, /* dir_action */
-	(void*)(ptrdiff_t)(strlen(path) + 1),
-	0);
-	} else {
-	DIR *dp;
-	struct dirent *ep;
-
-	dp = warn_opendir(path);
-	while ((ep = readdir(dp))) {
-	if (!strcmp(ep->d_name, "..") \|\| LONE_CHAR(ep->d_name, '.'))
-	continue;
-	add_to_dirlist(ep->d_name, NULL, (void*)(int)0, 0);
-	}
-	closedir(dp);
+	if (!(option_mask32 & FLAG(r)) && depth) {
+	add_to_dirlist(filename, sb, userdata, depth);
+	return SKIP;
	}
-
-	/* Sort dl alphabetically. */
-	qsort_string_vector(dl, dl_count);
-
-	dl[dl_count] = NULL;
-	return dl;
+	return TRUE;
	}

-
-	static void diffdir(char p1, char p2)
+	static void diffdir(char p[2], const char s_start)
	{
-	char dirlist1, dirlist2;
-	char dp1, dp2;
-	int pos;
-
-	/* Check for trailing slashes. */
-	dp1 = last_char_is(p1, '/');
-	if (dp1 != NULL)
-	*dp1 = '\0';
-	dp2 = last_char_is(p2, '/');
-	if (dp2 != NULL)
-	*dp2 = '\0';
-
-	/* Get directory listings for p1 and p2. */
-	dirlist1 = get_recursive_dirlist(p1);
-	dirlist2 = get_recursive_dirlist(p2);
-
-	/* If -S was set, find the starting point. */
-	if (opt_S_start) {
-	while (dirlist1 != NULL && strcmp(dirlist1, opt_S_start) < 0)
-	dirlist1++;
-	while (dirlist2 != NULL && strcmp(dirlist2, opt_S_start) < 0)
-	dirlist2++;
-	if ((dirlist1 == NULL) \|\| (dirlist2 == NULL))
-	bb_error_msg(bb_msg_invalid_arg, "NULL", "-S");
+	struct dlist list[2];
+
+	memset(&list, 0, sizeof(list));
+	for (int i = 0; i < 2; i++) {
+	/list[i].s = list[i].e = 0; - memset did it /
+	/list[i].dl = NULL; /
+
+	/* We need to trim root directory prefix.
+	* Using list.len to specify its length,
+	* add_to_dirlist will remove it. */
+	list[i].len = strlen(p[i]);
+	recursive_action(p[i], ACTION_RECURSE \| ACTION_FOLLOWLINKS,
+	add_to_dirlist, skip_dir, &list[i], 0);
+	/* Sort dl alphabetically.
+	* GNU diff does this ignoring any number of trailing dots.
+	* We don't, so for us dotted files almost always are
+	* first on the list.
+	*/
+	qsort_string_vector(list[i].dl, list[i].e);
+	/* If -S was set, find the starting point. */
+	if (!s_start)
+	continue;
+	while (list[i].s < list[i].e && strcmp(list[i].dl[list[i].s], s_start) < 0)
+	list[i].s++;
	}
-
	/* Now that both dirlist1 and dirlist2 contain sorted directory
	* listings, we can start to go through dirlist1. If both listings
	* contain the same file, then do a normal diff. Otherwise, behaviour
	* is determined by whether the -N flag is set. */
-	while (dirlist1 != NULL \|\| dirlist2 != NULL) {
-	dp1 = *dirlist1;
-	dp2 = *dirlist2;
-	pos = dp1 == NULL ? 1 : (dp2 == NULL ? -1 : strcmp(dp1, dp2));
+	while (1) {
+	char *dp[2];
+	int pos;
+	int k;
+
+	dp[0] = list[0].s < list[0].e ? list[0].dl[list[0].s] : NULL;
+	dp[1] = list[1].s < list[1].e ? list[1].dl[list[1].s] : NULL;
+	if (!dp[0] && !dp[1])
+	break;
+	pos = !dp[0] ? 1 : (!dp[1] ? -1 : strcmp(dp[0], dp[1]));
+	k = pos > 0;
+	if (pos && !(option_mask32 & FLAG(N)))
+	printf("Only in %s: %s\n", p[k], dp[k]);
+	else {
+	char fullpath[2], path[2]; /* if -N */
+
+	for (int i = 0; i < 2; i++) {
+	if (pos == 0 \|\| i == k) {
+	path[i] = fullpath[i] = concat_path_file(p[i], dp[i]);
+	stat(fullpath[i], &stb[i]);
+	} else {
+	fullpath[i] = concat_path_file(p[i], dp[1 - i]);
+	path[i] = (char *)bb_dev_null;
+	}
+	}
+	if (pos)
+	stat(fullpath[k], &stb[1 - k]);
+
+	if (S_ISDIR(stb[0].st_mode) && S_ISDIR(stb[1].st_mode))
+	printf("Common subdirectories: %s and %s\n", fullpath[0], fullpath[1]);
+	else if (!S_ISREG(stb[0].st_mode) && !S_ISDIR(stb[0].st_mode))
+	printf("File %s is not a regular file or directory and was skipped\n", fullpath[0]);
+	else if (!S_ISREG(stb[1].st_mode) && !S_ISDIR(stb[1].st_mode))
+	printf("File %s is not a regular file or directory and was skipped\n", fullpath[1]);
+	else if (S_ISDIR(stb[0].st_mode) != S_ISDIR(stb[1].st_mode)) {
+	if (S_ISDIR(stb[0].st_mode))
+	printf("File %s is a %s while file %s is a %s\n", fullpath[0], "directory", fullpath[1], "regular file");
+	else
+	printf("File %s is a %s while file %s is a %s\n", fullpath[0], "regular file", fullpath[1], "directory");
+	} else
+	print_status(diffreg(path), fullpath);
+
+	free(fullpath[0]);
+	free(fullpath[1]);
+	}
+	free(dp[k]);
+	list[k].s++;
	if (pos == 0) {
-	do_diff(p1, dp1, p2, dp2);
-	dirlist1++;
-	dirlist2++;
-	} else if (pos < 0) {
-	if (option_mask32 & FLAG_N)
-	do_diff(p1, dp1, p2, NULL);
-	else
-	print_only(p1, dp1);
-	dirlist1++;
-	} else {
-	if (option_mask32 & FLAG_N)
-	do_diff(p1, NULL, p2, dp2);
-	else
-	print_only(p2, dp2);
-	dirlist2++;
+	free(dp[1 - k]);
+	list[1 - k].s++;
	}
	}
+	if (ENABLE_FEATURE_CLEAN_UP) {
+	free(list[0].dl);
+	free(list[1].dl);
+	}
	}
	#endif

-
	int diff_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
	int diff_main(int argc UNUSED_PARAM, char **argv)
	{
	int gotstdin = 0;
-	char f1, f2;
+	char file[2], s_start = NULL;
	llist_t *L_arg = NULL;

	INIT_G();
@@ -1280,65 +874,49 @@ int diff_main(int argc UNUSED_PARAM, char **argv)
	opt_complementary = "=2:L::U+";
	getopt32(argv, "abdiL:NqrsS:tTU:wu"
	"p" /* ignored (for compatibility) */,
-	&L_arg, &opt_S_start, &opt_U_context);
-	/argc -= optind;/
+	&L_arg, &s_start, &opt_U_context);
	argv += optind;
	while (L_arg) {
-	if (label1 && label2)
+	if (label[0] && label[1])
	bb_show_usage();
-	if (label1) /* then label2 is NULL */
-	label2 = label1;
-	label1 = llist_pop(&L_arg);
+	if (label[0]) /* then label[1] is NULL */
+	label[1] = label[0];
+	label[0] = llist_pop(&L_arg);
	}
-
-	/*
-	* Do sanity checks, fill in stb1 and stb2 and call the appropriate
-	* driver routine. Both drivers use the contents of stb1 and stb2.
-	*/
-	f1 = argv[0];
-	f2 = argv[1];
-	/* Compat: "diff file name_which_doesnt_exist" exits with 2 */
	xfunc_error_retval = 2;
-	if (LONE_DASH(f1)) {
-	fstat(STDIN_FILENO, &stb1);
-	gotstdin++;
-	} else
-	xstat(f1, &stb1);
-	if (LONE_DASH(f2)) {
-	fstat(STDIN_FILENO, &stb2);
-	gotstdin++;
-	} else
-	xstat(f2, &stb2);
+	for (int i = 0; i < 2; i++) {
+	file[i] = argv[i];
+	/* Compat: "diff file name_which_doesnt_exist" exits with 2 */
+	if (LONE_DASH(file[i])) {
+	fstat(STDIN_FILENO, &stb[i]);
+	gotstdin++;
+	} else
+	xstat(file[i], &stb[i]);
+	}
	xfunc_error_retval = 1;
-
-	if (gotstdin && (S_ISDIR(stb1.st_mode) \|\| S_ISDIR(stb2.st_mode)))
+	if (gotstdin && (S_ISDIR(stb[0].st_mode) \|\| S_ISDIR(stb[1].st_mode)))
	bb_error_msg_and_die("can't compare stdin to a directory");

-	if (S_ISDIR(stb1.st_mode) && S_ISDIR(stb2.st_mode)) {
+	if (S_ISDIR(stb[0].st_mode) && S_ISDIR(stb[1].st_mode)) {
	#if ENABLE_FEATURE_DIFF_DIR
-	diffdir(f1, f2);
-	return exit_status;
+	diffdir(file, s_start);
	#else
	bb_error_msg_and_die("no support for directory comparison");
	#endif
-	}
+	} else {
+	bool dirfile = S_ISDIR(stb[0].st_mode) \|\| S_ISDIR(stb[1].st_mode);
+	bool dir = S_ISDIR(stb[1].st_mode);
+	if (dirfile) {
+	const char *slash = strrchr(file[!dir], '/');
+	file[dir] = concat_path_file(file[dir], slash ? slash + 1 : file[!dir]);
+	xstat(file[dir], &stb[dir]);
+	}
+	/* diffreg can get non-regular files here */
+	print_status(gotstdin > 1 ? STATUS_SAME : diffreg(file), file);

-	if (S_ISDIR(stb1.st_mode)) { /* "diff dir file" */
-	/* NB: "diff dir dir2/dir3/file" must become
-	* "diff dir/file dir2/dir3/file" */
-	char *slash = strrchr(f2, '/');
-	f1 = concat_path_file(f1, slash ? slash + 1 : f2);
-	xstat(f1, &stb1);
-	}
-	if (S_ISDIR(stb2.st_mode)) {
-	char *slash = strrchr(f1, '/');
-	f2 = concat_path_file(f2, slash ? slash + 1 : f1);
-	xstat(f2, &stb2);
+	if (dirfile)
+	free(file[dir]);
	}

-	/* diffreg can get non-regular files here,
-	* they are not both DIRestories */
-	print_status((gotstdin > 1 ? D_SAME : diffreg(f1, f2, 0)),
-	f1, f2 /, NULL/);
	return exit_status;
	}

testsuite/diff.tests+0 -3

@@ -44,21 +44,18 @@ testing "diff of stdin, twice" \
	"" \
	"stdin"

-	test x"$SKIP_KNOWN_BUGS" = x"" && \
	testing "diff -b treats EOF as whitespace" \
	'diff -ub - input; echo $?' \
	"0\n" \
	"abc" \
	"abc "

-	test x"$SKIP_KNOWN_BUGS" = x"" && \
	testing "diff -b treats all spaces as equal" \
	'diff -ub - input; echo $?' \
	"0\n" \
	"a \t c\n" \
	"a\t \tc\n"

-	test x"$SKIP_KNOWN_BUGS" = x"" && \
	testing "diff always takes context from old file" \
	"diff -ub - input \| $TRIM_TAB" \
	"\