radare2/libr/util/udiff.c

/* radare - LGPL - Copyright 2009-2022 - pancake, nikolai */

#include <r_util/r_diff.h>

// the non-system-diff doesnt work well
#define USE_SYSTEM_DIFF 1

R_API RDiff *r_diff_new_from(ut64 off_a, ut64 off_b) {
	RDiff *d = R_NEW0 (RDiff);
	if (d) {
		d->delta = 1;
		d->user = NULL;
		d->off_a = off_a;
		d->off_b = off_b;
		d->diff_cmd = strdup ("diff -au");
	}
	return d;
}

R_API RDiff *r_diff_new(void) {
	return r_diff_new_from (0, 0);
}

R_API void r_diff_free(RDiff *d) {
	if (d) {
		free (d->diff_cmd);
		free (d);
	}
}

R_API int r_diff_set_callback(RDiff *d, RDiffCallback callback, void *user) {
	d->callback = callback;
	d->user = user;
	return 1;
}

R_API int r_diff_set_delta(RDiff *d, int delta) {
	d->delta = delta;
	return 1;
}

typedef struct levrow {
	ut32 *changes;
	ut32 start, end;
} Levrow;

static void lev_matrix_free(Levrow *matrix, ut32 len) {
	size_t i;
	for (i = 0; i < len; i++) {
		free (matrix[i].changes);
	}
	free (matrix);
}

static inline void lev_row_adjust(Levrow *row, ut32 maxdst, ut32 rownum, ut32 buflen, ut32 delta) {
	delta += rownum;
	ut64 end = (ut64)delta + maxdst;
	row->end = R_MIN (end, buflen);
	row->start = delta <= maxdst? 0: delta - maxdst;
}

static inline Levrow *lev_row_init(Levrow *matrix, ut32 maxdst, ut32 rownum, ut32 buflen, ut32 delta) {
	R_RETURN_VAL_IF_FAIL (matrix && !matrix[rownum].changes, false);
	Levrow *row = matrix + rownum;
	lev_row_adjust (row, maxdst, rownum, buflen, delta);
	if ((row->changes = R_NEWS (ut32, row->end - row->start + 1)) == NULL) {
		return NULL;
	}
	return row;
}

static inline ut32 lev_get_val(Levrow *row, ut32 i) {
	if (i >= row->start && i <= row->end) {
		return row->changes[i - row->start];
	}
	return UT32_MAX - 1; // -1 so a +1 with sub weight does not overflow
}

// obtains array of operations, in reverse order, to get from column to row of
// matrix
static st32 lev_parse_matrix(Levrow *matrix, ut32 len, bool invert, RLevOp **chgs) {
	R_RETURN_VAL_IF_FAIL (len >= 2 && matrix && chgs && !*chgs, -1);
	Levrow *row = matrix + len - 1;
	Levrow *prev_row = row - 1;
	RLevOp a = LEVADD;
	RLevOp d = LEVDEL;
	if (invert) {
		a = LEVDEL;
		d = LEVADD;
	}

	const size_t overflow = (size_t)-1 / (2 * sizeof (RLevOp));
	int j = row->end;
	size_t size = j;
	RLevOp *changes = R_NEWS (RLevOp, size);
	if (!changes) {
		return -1;
	}

	size_t insert = 0;
	while (row != matrix) { // matrix[0] is not processed
		ut32 sub = lev_get_val (prev_row, j - 1);
		ut32 del = lev_get_val (prev_row, j);
		ut32 add = lev_get_val (row, j - 1);

		if (insert >= size) {
			if (size >= overflow) {
				// overflow paranoia
				free (changes);
				return -1;
			}
			size *= 2;
			RLevOp *tmp = realloc (changes, size * sizeof (RLevOp));
			if (!tmp) {
				free (changes);
				return -1;
			}
			changes = tmp;
		}

		if (sub <= del && sub <= add) {
			if (sub == lev_get_val (row, j)) {
				changes[insert++] = LEVNOP;
			} else {
				changes[insert++] = LEVSUB;
			}
			j--;
		} else if (del <= add && del <= sub) {
			changes[insert++] = d;
		} else {
			changes[insert++] = a;
			j--;
			continue; // continue with same rows
		}
		free (row->changes);
		row->changes = NULL;
		row = prev_row--;
	}
	if (size - insert < j) {
		if (size > overflow) {
			// overly paranoid
			free (changes);
			return -1;
		}
		size += j - (size - insert);
		RLevOp *tmp = realloc (changes, size * sizeof (RLevOp));
		if (!tmp) {
			free (changes);
			return -1;
		}
		changes = tmp;
	}
	while (j > 0) {
		changes[insert++] = a;
		j--;
	}

	*chgs = changes;
	return insert;
}

static inline void lev_fill_changes(RLevOp *chgs, RLevOp op, ut32 count) {
	while (count > 0) {
		count--;
		chgs[count] = op;
	}
}

typedef struct {
	RDiff *d;
	char *str;
} RDiffUser;

#if USE_SYSTEM_DIFF
R_API char *r_diff_buffers_tostring(RDiff *d, const ut8 *a, int la, const ut8 *b, int lb) {
	return r_diff_buffers_unified (d, a, la, b, lb);
}

#else
// XXX buffers_static doesnt constructs the correct string in this callback
static int tostring(RDiff *d, void *user, RDiffOp *op) {
	RDiffUser *u = (RDiffUser *)user;
	if (op->a_len > 0) {
		char *a_str = r_str_ndup ((const char *)op->a_buf + op->a_off, op->a_len);
		u->str = r_str_appendf (u->str, "+(%s)", a_str);
#if 0
		char *bufasm = r_str_prefix_all (a_str, "- ");
		u->str = r_str_appendf (u->str, "-(%s)", bufasm);
		free (bufasm);
#endif
		free (a_str);
	}
	if (op->b_len > 0) {
		char *b_str = r_str_ndup ((const char *)op->b_buf + op->b_off, op->b_len);
		u->str = r_str_appendf (u->str, "+(%s)", b_str);
#if 0
		char *bufasm = r_str_prefix_all (b_str, "+ ");
		u->str = r_str_appendf (u->str, "+(%s)", bufasm);
		free (bufasm);
#endif
		free (b_str);
	}
	if (op->a_len == op->b_len) {
		char *b_str = r_str_ndup ((const char *)op->a_buf + op->a_off, op->a_len);
		// char *bufasm = r_str_prefix_all (b_str, "  ");
		u->str = r_str_appendf (u->str, "%s", b_str);
		// free (bufasm);
		free (b_str);
	}
	return 1;
}

R_API char *r_diff_buffers_tostring(RDiff *d, const ut8 *a, int la, const ut8 *b, int lb) {
	// XXX buffers_static doesnt constructs the correct string in this callback
	void *c = d->callback;
	void *u = d->user;
	RDiffUser du = {d, strdup ("")};
	d->callback = &tostring;
	d->user = &du;
	r_diff_buffers_static (d, a, la, b, lb);
	d->callback = c;
	d->user = u;
	return du.str;
}
#endif

#define diffHit() { \
	const size_t i_hit = i - hit; \
	int ra = la - i_hit; \
	int rb = lb - i_hit; \
	struct r_diff_op_t o = { \
		.a_off = d->off_a+i-hit, .a_buf = a+i-hit, .a_len = R_MIN (hit, ra), \
		.b_off = d->off_b+i-hit, .b_buf = b+i-hit, .b_len = R_MIN (hit, rb) \
	}; \
	d->callback (d, d->user, &o); \
}

R_API int r_diff_buffers_static(RDiff *d, const ut8 *a, int la, const ut8 *b, int lb) {
	int i, len;
	int hit = 0;
	la = R_ABS (la);
	lb = R_ABS (lb);
	if (la != lb) {
		len = R_MIN (la, lb);
		R_LOG_INFO ("Buffer truncated to %d byte(s) (%d not compared)", len, R_ABS(lb - la));
	} else {
		len = la;
	}
	for (i = 0; i < len; i++) {
		if (a[i] != b[i]) {
			hit++;
		} else {
			if (hit > 0) {
				diffHit ();
				hit = 0;
			}
		}
	}
	if (hit > 0) {
		diffHit ();
	}
	return 0;
}

R_API char *r_diff_buffers_unified(RDiff *d, const ut8 *a, int la, const ut8 *b, int lb) {
	char *fa = NULL;
	char *fb = NULL;
	int fd = r_file_mkstemp ("r_diff", &fa);
	int fe = r_file_mkstemp ("r_diff", &fb);
	if (fd == -1 || fe == -1) {
		R_LOG_ERROR ("Failed to create temporary files");
		return NULL;
	}
	if (!fa || !fb) {
		R_LOG_ERROR ("fafb nul");
		free (fa);
		free (fb);
		return NULL;
	}
	r_file_dump (fa, a, la, 0);
	r_file_dump (fb, b, lb, 0);
#if 0
	if (r_mem_is_printable (a, R_MIN (5, la))) {
		r_file_dump (fa, a, la, 0);
		r_file_dump (fb, b, lb, 0);
	} else {
		r_file_hexdump (fa, a, la, 0);
		r_file_hexdump (fb, b, lb, 0);
	}
#endif
	char *err = NULL;
	char *out = NULL;
	int out_len;
	char *diff_cmdline = r_str_newf ("%s %s %s", d->diff_cmd, fa, fb);
	if (diff_cmdline) {
		(void)r_sys_cmd_str_full (diff_cmdline, NULL, 0, &out, &out_len, &err);
		free (diff_cmdline);
	}
	close (fd);
	close (fe);
	r_file_rm (fa);
	r_file_rm (fb);
	free (fa);
	free (fb);
	free (err);
	return out;
}

R_API int r_diff_buffers(RDiff *d, const ut8 *a, ut32 la, const ut8 *b, ut32 lb) {
	return d->delta
		? r_diff_buffers_delta (d, a, la, b, lb)
		: r_diff_buffers_static (d, a, la, b, lb);
}

// Eugene W. Myers O(ND) diff algorithm
// Returns edit distance with costs: insertion=1, deletion=1, no substitution
R_API bool r_diff_buffers_distance_myers(RDiff *diff, const ut8 *a, ut32 la, const ut8 *b, ut32 lb, ut32 *distance, double *similarity) {
	R_RETURN_VAL_IF_FAIL (a && b, false);
	const bool verbose = diff? diff->verbose: false;
	const ut32 length = la + lb;
	const ut8 *ea = a + la, *eb = b + lb;
	// Strip prefix
	for (; a < ea && b < eb && *a == *b; a++, b++) {}
	// Strip suffix
	for (; a < ea && b < eb && ea[-1] == eb[-1]; ea--, eb--) {}
	la = ea - a;
	lb = eb - b;
	ut32 *v0, *v;
	st64 m = (st64)la + lb, di = 0, low, high, i, x, y;
	if (m + 2 > SIZE_MAX / sizeof (st64) || !(v0 = malloc ((m + 2) * sizeof (ut32)))) {
		return false;
	}
	v = v0 + lb;
	v[1] = 0;
	for (di = 0; di <= m; di++) {
		low = -di + 2 * R_MAX (0, di - (st64)lb);
		high = di - 2 * R_MAX (0, di - (st64)la);
		for (i = low; i <= high; i += 2) {
			x = i == -di || (i != di && v[i-1] < v[i+1]) ? v[i+1] : v[i-1] + 1;
			y = x - i;
			while (x < la && y < lb && a[x] == b[y]) {
				x++;
				y++;
			}
			v[i] = x;
			if (x == la && y == lb) {
				goto out;
			}
		}
		if (verbose && di % 10000 == 0) {
			eprintf ("\rProcessing dist %" PFMT64d " of max %" PFMT64d "\r", (st64)di, (st64)m);
		}
	}

out:
	if (verbose) {
		eprintf ("\n");
	}
	free (v0);
	//Clean up output on loop exit (purely aesthetic)
	if (distance) {
		*distance = di;
	}
	if (similarity) {
		*similarity = length ? 1.0 - (double)di / length : 1.0;
	}
	return true;
}

R_API bool r_diff_buffers_distance_levenshtein(RDiff *diff, const ut8 *a, ut32 la, const ut8 *b, ut32 lb, ut32 *distance, double *similarity) {
	R_RETURN_VAL_IF_FAIL (a && b, false);
	const bool verbose = diff ? diff->verbose : false;
	const ut32 length = R_MAX (la, lb);
	const ut8 *ea = a + la, *eb = b + lb, *t;
	ut32 *d, i, j;
	// Strip prefix
	for (; a < ea && b < eb && *a == *b; a++, b++) {}
	// Strip suffix
	for (; a < ea && b < eb && ea[-1] == eb[-1]; ea--, eb--) {}
	la = ea - a;
	lb = eb - b;
	if (la < lb) {
		i = la;
		la = lb;
		lb = i;
		t = a;
		a = b;
		b = t;
	}

	if (sizeof (ut32) > SIZE_MAX / (lb + 1) || !(d = malloc ((lb + 1) * sizeof (ut32)))) {
		return false;
	}
	for (i = 0; i <= lb; i++) {
		d[i] = i;
	}
	for (i = 0; i < la; i++) {
		ut32 ul = d[0];
		d[0] = i + 1;
		for (j = 0; j < lb; j++) {
			ut32 u = d[j + 1];
			d[j + 1] = a[i] == b[j] ? ul : R_MIN (ul, R_MIN (d[j], u)) + 1;
			ul = u;
		}
		if (verbose && i % 10000 == 0) {
			eprintf ("\rProcessing %" PFMT32u " of %" PFMT32u "\r", i, la);
		}
	}

	if (verbose) {
		eprintf ("\n");
	}
	if (distance) {
		*distance = d[lb];
	}
	if (similarity) {
		*similarity = length ? 1.0 - (double)d[lb] / length : 1.0;
	}
	free (d);
	return true;
}

R_API bool r_diff_buffers_distance(RDiff *d, const ut8 *a, ut32 la, const ut8 *b, ut32 lb, ut32 *distance, double *similarity) {
	if (d) {
		switch (d->type) {
		case 'm':
			return r_diff_buffers_distance_myers (d, a, la, b, lb, distance, similarity);
		case 'l':
		default:
			break;
		}
	}
	return r_diff_buffers_distance_levenshtein (d, a, la, b, lb, distance, similarity);
}

// Use Needleman–Wunsch to diffchar.
// This is an O(mn) algo in both space and time.
// Note that 64KB * 64KB * 2 = 8GB.
// TODO Discard common prefix and suffix
R_API RDiffChar *r_diffchar_new(const ut8 *a, const ut8 *b) {
	R_RETURN_VAL_IF_FAIL (a && b, NULL);
	RDiffChar *diffchar = R_NEW0 (RDiffChar);
	if (!diffchar) {
		return NULL;
	}

	const size_t len_a = strlen ((const char *)a);
	const size_t len_b = strlen ((const char *)b);
	const size_t len_long = len_a > len_b ? len_a : len_b;
	const size_t dim = len_long + 1;
	char *dup_a = malloc (len_long);
	char *dup_b = malloc (len_long);
	st16 *align_table = malloc (dim * dim * sizeof (st16));
	ut8 *align_a = malloc (2 * len_long);
	ut8 *align_b = malloc (2 * len_long);
	if (!(dup_a && dup_b && align_table && align_a && align_b)) {
		free (dup_a);
		free (dup_b);
		free (align_table);
		free (align_a);
		free (align_b);
		free (diffchar);
		return NULL;
	}

	snprintf (dup_a, len_long, "%s", a);
	a = (const ut8*)dup_a;
	snprintf (dup_b, len_long, "%s", b);
	b = (const ut8*)dup_b;

	// Fill table
	size_t row, col;
	*align_table = 0;
	for (row = 1; row < dim; row++) {
		// TODO Clamping [ST16_MIN + 1, .]
		*(align_table + row) = *(align_table + row * dim) = -(st16)row;
	}
	const st16 match = 1;
	const st16 match_nl = 2;
	const st16 mismatch = -2;
	const st16 gap = -1;
	for (row = 1; row < dim; row++) {
		for (col = 1; col < dim; col++) {
			// TODO Clamping [ST16_MIN + 1, ST16_MAX]
			const ut8 a_ch = a[col - 1];
			const ut8 b_ch = b[row - 1];
			const st16 tl_score = *(align_table + (row - 1) * dim + col - 1)
				+ (a_ch == b_ch
					? (a_ch == '\n'
						? match_nl
						: match)
					: mismatch);
			const st16 t_score = *(align_table + (row - 1) * dim + col) + gap;
			const st16 l_score = *(align_table + row * dim + col - 1) + gap;
			st16 score;
			if (tl_score >= t_score && tl_score >= l_score) {
				score = tl_score;
			} else if (t_score >= tl_score && t_score >= l_score) {
				score = t_score;
			} else {
				score = l_score;
			}
			*(align_table + row * dim + col) = score;
		}
	}

#if 0
	// Print table (Debug)
	char char_str[3] = { ' ' };
	printf ("%4s ", char_str);
	for (col = 0; col < dim; col++) {
		if (col && a[col - 1] == '\n') {
			char_str[0] = '\\';
			char_str[1] = 'n';
		} else {
			char_str[0] = col ? a[col - 1] : ' ';
			char_str[1] = 0;
		}
		printf ("%4s ", char_str);
	}
	printf ("\n");
	for (row = 0; row < dim; row++) {
		if (row && b[row - 1] == '\n') {
			char_str[0] = '\\';
			char_str[1] = 'n';
		} else {
			char_str[0] = row ? b[row - 1] : ' ';
			char_str[1] = 0;
		}
		printf ("%4s ", char_str);
		for (col = 0; col < dim; col++) {
			printf ("%4d ", *(align_table + row * dim + col));
		}
		printf ("\n");
	}
#endif

	// Do alignment
	size_t idx_a = len_long - 1;
	size_t idx_b = len_long - 1;
	size_t idx_align = 2 * len_long - 1;
	size_t pos_row = dim - 1;
	size_t pos_col = dim - 1;
	while (pos_row || pos_col) {
		const st16 tl_score = (pos_row > 0 && pos_col > 0) ?
				*(align_table + (pos_row - 1) * dim + pos_col - 1) :
				ST16_MIN;
		const st16 t_score = pos_row > 0 ?
				*(align_table + (pos_row - 1) * dim + pos_col) :
				ST16_MIN;
		const st16 l_score = pos_col > 0 ?
				*(align_table + pos_row * dim + pos_col - 1) :
				ST16_MIN;
		const bool match = a[idx_a] == b[idx_b];
		if (t_score >= l_score && (!match || t_score >= tl_score)) {
			align_a[idx_align] = 0;
			align_b[idx_align] = b[idx_b--];
			idx_align--;
			pos_row--;
		} else if (l_score >= t_score && (!match || l_score >= tl_score)) {
			align_a[idx_align] = a[idx_a--];
			align_b[idx_align] = 0;
			idx_align--;
			pos_col--;
		} else {
			align_a[idx_align] = a[idx_a--];
			align_b[idx_align] = b[idx_b--];
			idx_align--;
			pos_row--;
			pos_col--;
		}
	}
	idx_align++;
	const size_t start_align = idx_align;

#if 0
	// Print alignment (Debug)
	for (; idx_align < 2 * len_long; idx_align++) {
		const ut8 ch = align_a[idx_align];
		if (align_b[idx_align] == '\n' && ch != '\n') {
			printf (ch ? " " : "-");
		}
		if (ch == 0) {
			printf ("-");
		} else if (ch == '\n') {
			printf ("\\n");
		} else {
			printf ("%c", ch);
		}
	}
	printf ("\n");
	for (idx_align = start_align; idx_align < 2 * len_long; idx_align++) {
		const ut8 ch = align_b[idx_align];
		if (align_a[idx_align] == '\n' && ch != '\n') {
			printf (ch ? " " : "-");
		}
		if (ch == 0) {
			printf ("-");
		} else if (ch == '\n') {
			printf ("\\n");
		} else {
			printf ("%c", ch);
		}
	}
	printf ("\n");
#endif

	diffchar->align_a = align_a;
	diffchar->align_b = align_b;
	diffchar->len_buf = len_long;
	diffchar->start_align = start_align;
	free (dup_a);
	free (dup_b);
	free (align_table);
	return diffchar;
}

typedef enum {
	R2R_ALIGN_MATCH, R2R_ALIGN_MISMATCH, R2R_ALIGN_TOP_GAP, R2R_ALIGN_BOTTOM_GAP
} R2RCharAlignment;

typedef enum {
	R2R_DIFF_MATCH, R2R_DIFF_DELETE, R2R_DIFF_INSERT
} R2RPrintDiffMode;

R_API void r_diffchar_print(RDiffChar *diffchar) {
	R_RETURN_IF_FAIL (diffchar);
	R2RPrintDiffMode cur_mode = R2R_DIFF_MATCH;
	R2RCharAlignment cur_align;
	size_t idx_align = diffchar->start_align;
	while (idx_align < 2 * diffchar->len_buf) {
		const ut8 a_ch = diffchar->align_a[idx_align];
		const ut8 b_ch = diffchar->align_b[idx_align];
		if (a_ch && !b_ch) {
			cur_align = R2R_ALIGN_BOTTOM_GAP;
		} else if (!a_ch && b_ch) {
			cur_align = R2R_ALIGN_TOP_GAP;
		} else if (a_ch != b_ch) {
			R_LOG_ERROR ("Internal mismatch detected!");
			cur_align = R2R_ALIGN_MISMATCH;
		} else {
			cur_align = R2R_ALIGN_MATCH;
		}
		if (cur_mode == R2R_DIFF_MATCH) {
			if (cur_align == R2R_ALIGN_MATCH) {
				if (a_ch) {
					printf ("%c", a_ch);
				}
			} else if (cur_align == R2R_ALIGN_BOTTOM_GAP) {
				printf (a_ch == '\n'
						? "%c" Color_HLDELETE
						: Color_HLDELETE "%c",
					a_ch);
				cur_mode = R2R_DIFF_DELETE;
			} else if (cur_align == R2R_ALIGN_TOP_GAP) {
				printf (b_ch == '\n'
						? "%c" Color_HLINSERT
						: Color_HLINSERT "%c",
					b_ch);
				cur_mode = R2R_DIFF_INSERT;
			}
		} else if (cur_mode == R2R_DIFF_DELETE) {
			if (cur_align == R2R_ALIGN_MATCH) {
				printf (Color_RESET);
				if (a_ch) {
					printf ("%c", a_ch);
				}
				cur_mode = R2R_DIFF_MATCH;
			} else if (cur_align == R2R_ALIGN_BOTTOM_GAP) {
				printf (a_ch == '\n'
						? Color_RESET "%c" Color_HLDELETE
						: "%c",
					a_ch);
			} else if (cur_align == R2R_ALIGN_TOP_GAP) {
				printf (b_ch == '\n'
						? Color_RESET "%c" Color_HLINSERT
						: Color_HLINSERT "%c",
					b_ch);
				cur_mode = R2R_DIFF_INSERT;
			}
		} else if (cur_mode == R2R_DIFF_INSERT) {
			if (cur_align == R2R_ALIGN_MATCH) {
				printf (Color_RESET);
				if (a_ch) {
					printf ("%c", a_ch);
				}
				cur_mode = R2R_DIFF_MATCH;
			} else if (cur_align == R2R_ALIGN_BOTTOM_GAP) {
				printf (a_ch == '\n'
						? Color_RESET "%c" Color_HLDELETE
						: Color_HLDELETE "%c",
					a_ch);
				cur_mode = R2R_DIFF_DELETE;
			} else if (cur_align == R2R_ALIGN_TOP_GAP) {
				printf (b_ch == '\n'
						? Color_RESET "%c" Color_HLINSERT
						: "%c",
					b_ch);
			}
		}
		idx_align++;
	}
	printf (Color_RESET "\n");
}

R_API void r_diffchar_free(RDiffChar *diffchar) {
	if (diffchar) {
		free ((ut8 *)diffchar->align_a);
		free ((ut8 *)diffchar->align_b);
		free (diffchar);
	}
}

static st32 r_diff_levenshtein_nopath(RLevBuf *bufa, RLevBuf *bufb, ut32 maxdst, RLevMatches levdiff, size_t skip, ut32 alen, ut32 blen) {
	R_RETURN_VAL_IF_FAIL (bufa && bufb && bufa->buf && bufb->buf, -1);
	R_RETURN_VAL_IF_FAIL (blen >= alen && alen > 0, -1);

	// max distance is at most length of longer input, or provided by user
	ut32 origdst = maxdst = R_MIN (maxdst, blen);

	// two rows
	Levrow *matrix = R_NEWS0 (Levrow, 2);
	if (!matrix) {
		return -1;
	}

	Levrow *row = matrix;
	Levrow *prev_row = matrix + 1;
	// must allocate for largest row, not the first row, so don't use
	// lev_row_init
	row->changes = R_NEWS (ut32, 2 * maxdst + 1);
	prev_row->changes = R_NEWS (ut32, 2 * maxdst + 1);
	if (!prev_row->changes || !row->changes) {
		lev_matrix_free (matrix, alen + 1);
		return -1;
	}

	ut32 ldelta = blen - alen;
	if (ldelta > maxdst) {
		lev_matrix_free (matrix, alen + 1);
		return ST32_MAX;
	}

	lev_row_adjust (row, maxdst, 0, blen, ldelta);
	size_t i;
	for (i = row->start; i <= row->end; i++) {
		row->changes[i] = i;
	}

	// do the rest of the rows
	ut32 oldmin = 0; // minimum cell in row 0
	for (i = 1; i <= alen; i++) { // loop through all rows
		// switch rows
		if (row == matrix) {
			row = prev_row;
			prev_row = matrix;
		} else {
			prev_row = row;
			row = matrix;
		}
		lev_row_adjust (row, maxdst, i, blen, ldelta);

		ut32 start = row->start;
		ut32 udel = UT32_MAX;
		if (start == 0) {
			row->changes[0] = udel = i;
			start++;
		}
		ut32 newmin = UT32_MAX;
		ut32 sub = lev_get_val (prev_row, start - 1);
		ut32 j;
		for (j = start; j <= row->end; j++) {
			ut32 add = lev_get_val (prev_row, j);
			ut32 ans = R_MIN (udel, add) + 1;
			if (ans >= sub) {
				// on rare occassions, when add/del is obviously better then
				// sub, we can skip levdiff call
				int d = levdiff (bufa, bufb, i + skip - 1, j + skip - 1)? 1: 0;
				ans = R_MIN (ans, sub + d);
			}
			sub = add;
			udel = ans;
			row->changes[j - row->start] = ans;
			if (ans < newmin) {
				newmin = ans;
			}
		}

		if (newmin > oldmin) {
			if (maxdst == 0) { // provided bad maxdst
				lev_matrix_free (matrix, 2);
				return ST32_MAX;
			}
			// if smallest element of this row is larger then the smallest
			// element of previous row a change must occur and thus the
			// distance for the rest of the alg can be reduced.
			oldmin = newmin;
			maxdst--;
		}
	}

	st32 ret = lev_get_val (row, row->end);
	if (ret > origdst) {
		ret = ST32_MAX;
	}
	lev_matrix_free (matrix, 2);
	return ret;
}

/**
 * \brief Return Levenshtein distance and put array of changes, of unknown
 * lenght, in chgs
 * \param bufa Structure to represent starting buffer
 * \param bufb Structure to represent the buffer to reach
 * \param maxdst Max Levenshtein distance need, send UT32_MAX if unknown.
 * \param levdiff Function pointer returning true when there is a difference.
 * \param chgs Returned array of changes to get from bufa to bufb
 *
 * Perform a Levenshtein diff on two buffers and obtain a RLevOp array of
 * changes. The length of the RLevOp array is NOT provided, it is terminated by
 * the LEVEND value. Providing a good maxdst value will increase performance of
 * this algorithm. If computed maxdst is exceeded ST32_MAX will be returned and
 * chgs will be left NULL. The chgs value must point to a NULL pointer. The
 * caller must free *chgs.
 */
R_API st32 r_diff_levenshtein_path(RLevBuf *bufa, RLevBuf *bufb, ut32 maxdst, RLevMatches levdiff, RLevOp **chgs) {
	R_RETURN_VAL_IF_FAIL (bufa && bufb && bufa->buf && bufb->buf, -1);
	R_RETURN_VAL_IF_FAIL (!chgs || !*chgs, -1); // if chgs then it must point at NULL

	// force buffer b to be longer, this will invert add/del resulsts
	bool invert = false;
	if (bufb->len < bufa->len) {
		invert = true;
		RLevBuf *x = bufa;
		bufa = bufb;
		bufb = x;
	}
	R_RETURN_VAL_IF_FAIL (bufb->len < UT32_MAX, -1);
	ut32 ldelta = bufb->len - bufa->len;
	if (ldelta > maxdst) {
		return ST32_MAX;
	}

	// Strip start as long as bytes don't diff
	size_t skip;
	ut32 alen = bufa->len;
	ut32 blen = bufb->len;
	for (skip = 0; skip < alen && !levdiff (bufa, bufb, skip, skip); skip++) {
	}

	// strip suffix as long as bytes don't diff
	size_t i;
	for (i = 0; alen > skip && !levdiff (bufa, bufb, alen - 1, blen - 1); alen--, blen--, i++) {}
	alen -= skip;
	blen -= skip;

	if (alen == 0) {
		if (chgs) {
			RLevOp *c = R_NEWS (RLevOp, skip + i + blen + 1);
			if (!c) {
				return -1;
			}
			*chgs = c;

			lev_fill_changes (c, LEVNOP, skip);
			c += skip;
			lev_fill_changes (c, invert? LEVDEL: LEVADD, blen);
			c += blen;
			lev_fill_changes (c, LEVNOP, i);
			c += i;

			*c = LEVEND;
		}
		return blen;
	}
	if (!chgs) {
		return r_diff_levenshtein_nopath (bufa, bufb, maxdst, levdiff, skip, alen, blen);
	}

	// max distance is at most length of longer input, or provided by user
	ut32 origdst = maxdst = R_MIN (maxdst, blen);

	// alloc array of rows
	Levrow *matrix = R_NEWS0 (Levrow, alen + 1);
	if (!matrix) {
		return -1;
	}

	// init row 0
	Levrow *row = lev_row_init (matrix, maxdst, 0, blen, ldelta);
	if (!row) {
		lev_matrix_free (matrix, alen + 1);
		return -1;
	}
	for (i = row->start; i <= row->end; i++) {
		row->changes[i] = i;
	}

	// do the rest of the rows
	ut32 oldmin = 0; // minimum cell in row 0
	Levrow *prev_row;
	for (i = 1; i <= alen; i++) { // loop through all rows
		prev_row = row;
		if ((row = lev_row_init (matrix, maxdst, i, blen, ldelta)) == NULL) {
			lev_matrix_free (matrix, alen + 1);
			return -1;
		}

		ut32 start = row->start;
		ut32 udel = UT32_MAX;
		if (start == 0) {
			row->changes[0] = udel = i;
			start++;
		}
		ut32 newmin = UT32_MAX;
		ut32 sub = lev_get_val (prev_row, start - 1);
		ut32 j;
		for (j = start; j <= row->end; j++) {
			ut32 add = lev_get_val (prev_row, j);
			ut32 ans = R_MIN (udel, add) + 1;
			if (ans >= sub) {
				// on rare occassions, when add/del is obviously better then
				// sub, we can skip levdiff call
				int d = levdiff (bufa, bufb, i + skip - 1, j + skip - 1)? 1: 0;
				ans = R_MIN (ans, sub + d);
			}
			sub = add;
			udel = ans;
			row->changes[j - row->start] = ans;
			if (ans < newmin) {
				newmin = ans;
			}
		}
		if (newmin > oldmin) {
			if (maxdst == 0) { // provided bad maxdst
				lev_matrix_free (matrix, alen + 1);
				return ST32_MAX;
			}
			// if smallest element of this row is larger then the smallest
			// element of previous row a change must occur and thus the
			// distance for the rest of the alg can be reduced.
			oldmin = newmin;
			maxdst--;
		}
	}

	st32 ret = lev_get_val (row, row->end);
	if (ret > origdst) {
		// can happen when off by one
		lev_matrix_free (matrix, alen + 1);
		return ST32_MAX;
	}

#if 0
	{
		// for debugging matrix
		size_t total = 0;
		for (i = 0; i <= alen; i++) {
			Levrow *bow = matrix + i;
			ut32 j;
			printf ("   ");
			for (j = 0; j <= blen; j++) {
				ut32 val = lev_get_val (bow, j);
				if (val >= UT32_MAX - 1) {
					printf (" ..");
				} else {
					printf (" %02x", val);
				}
			}
			total += bow->end + 1 - bow->start;
			printf ("  buflen: %d\n", bow->end + 1 - bow->start);
		}
		printf ("\n%ld matrix cells allocated\n", total);
	}
#endif

	RLevOp *mtxpath = NULL;
	st32 chg_size = lev_parse_matrix (matrix, alen + 1, invert, &mtxpath);
	lev_matrix_free (matrix, alen + 1);
	if (chg_size > 0 && mtxpath) {
		ut32 tail = bufb->len - skip - blen;
		RLevOp *c = R_NEWS (RLevOp, skip + chg_size + tail + 1);
		*chgs = c;
		if (c) {
			lev_fill_changes (c, LEVNOP, skip);
			c += skip;

			while (chg_size > 0) {
				chg_size--;
				*c = mtxpath[chg_size];
				c++;
			}
			lev_fill_changes (c, LEVNOP, tail);
			c += tail;
			*c = LEVEND;
		}
	}
	free (mtxpath);
	return ret;
}