--- /dev/null
+/* diff - compute a shortest edit script (SES) given two sequences
+ * Copyright (c) 2004 Michael B. Allen <mba2000 ioplex.com>
+ *
+ * The MIT License
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+/* This algorithm is basically Myers' solution to SES/LCS with
+ * the Hirschberg linear space refinement as described in the
+ * following publication:
+ *
+ * E. Myers, ``An O(ND) Difference Algorithm and Its Variations,''
+ * Algorithmica 1, 2 (1986), 251-266.
+ * http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps
+ *
+ * This is the same algorithm used by GNU diff(1).
+ */
+
+/* Copyright (c) 2010, Vsevolod Stakhov
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED ''AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL Rambler BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "diff.h"
+
+
+#define FV(k) _v(ctx, (k), 0)
+#define RV(k) _v(ctx, (k), 1)
+
+#define MAX_DIFF 1024
+
+struct _ctx
+{
+ GArray *buf;
+ GArray *ses;
+ gint si;
+ gint dmax;
+};
+
+struct middle_snake
+{
+ gint x, y, u, v;
+};
+
+static
+void maybe_resize_array(GArray *arr, guint k)
+{
+ if (k > arr->len) {
+ g_array_set_size (arr, k);
+ }
+
+}
+
+static void
+_setv(struct _ctx *ctx, gint k, gint r, gint val)
+{
+ gint j;
+ gint *i;
+ /* Pack -N to N ginto 0 to N * 2
+ */
+ j = k <= 0 ? -k * 4 + r : k * 4 + (r - 2);
+
+ maybe_resize_array (ctx->buf, j);
+ i = (gint *) &g_array_index (ctx->buf, gint, j);
+ *i = val;
+}
+
+static gint
+_v(struct _ctx *ctx, gint k, gint r)
+{
+ gint j;
+
+ j = k <= 0 ? -k * 4 + r : k * 4 + (r - 2);
+
+ return *((gint *) &g_array_index (ctx->buf, gint, j));
+}
+
+static gint
+_find_middle_snake(const void *a, gint aoff, gint n, const void *b,
+ gint boff, gint m, struct _ctx *ctx, struct middle_snake *ms)
+{
+ gint delta, odd, mid, d;
+
+ delta = n - m;
+ odd = delta & 1;
+ mid = (n + m) / 2;
+ mid += odd;
+
+ _setv (ctx, 1, 0, 0);
+ _setv (ctx, delta - 1, 1, n);
+
+ for (d = 0; d <= mid; d++) {
+ gint k, x, y;
+
+ if ((2 * d - 1) >= ctx->dmax) {
+ return ctx->dmax;
+ }
+
+ for (k = d; k >= -d; k -= 2) {
+ if (k == -d || (k != d && FV(k - 1) < FV(k + 1))) {
+ x = FV(k + 1);
+ }
+ else {
+ x = FV(k - 1) + 1;
+ }
+ y = x - k;
+
+ ms->x = x;
+ ms->y = y;
+ const guchar *a0 = (const guchar *) a + aoff;
+ const guchar *b0 = (const guchar *) b + boff;
+ while (x < n && y < m && a0[x] == b0[y]) {
+ x++;
+ y++;
+ }
+ _setv (ctx, k, 0, x);
+
+ if (odd && k >= (delta - (d - 1)) && k <= (delta + (d - 1))) {
+ if (x >= RV(k)) {
+ ms->u = x;
+ ms->v = y;
+ return 2 * d - 1;
+ }
+ }
+ }
+ for (k = d; k >= -d; k -= 2) {
+ gint kr = (n - m) + k;
+
+ if (k == d || (k != -d && RV(kr - 1) < RV(kr + 1))) {
+ x = RV(kr - 1);
+ }
+ else {
+ x = RV(kr + 1) - 1;
+ }
+ y = x - kr;
+
+ ms->u = x;
+ ms->v = y;
+ const guchar *a0 = (const guchar *) a + aoff;
+ const guchar *b0 = (const guchar *) b + boff;
+ while (x > 0 && y > 0 && a0[x - 1] == b0[y - 1]) {
+ x--;
+ y--;
+ }
+ _setv (ctx, kr, 1, x);
+
+ if (!odd && kr >= -d && kr <= d) {
+ if (x <= FV(kr)) {
+ ms->x = x;
+ ms->y = y;
+ return 2 * d;
+ }
+ }
+ }
+ }
+
+ errno = EFAULT;
+
+ return -1;
+}
+
+static void
+_edit(struct _ctx *ctx, gint op, gint off, gint len)
+{
+ struct diff_edit *e = NULL, newe;
+
+ if (len == 0 || ctx->ses == NULL) {
+ return;
+ }
+ /*
+ * Add an edit to the SES (or
+ * coalesce if the op is the same)
+ */
+ if (ctx->ses->len != 0) {
+ e = &g_array_index (ctx->ses, struct diff_edit, ctx->ses->len - 1);
+ }
+ if (e == NULL || e->op != op) {
+ newe.op = op;
+ newe.off = off;
+ newe.len = len;
+ g_array_append_val (ctx->ses, newe);
+ }
+ else {
+ e->len += len;
+ }
+}
+
+static gint
+_ses(const void *a, gint aoff, gint n, const void *b, gint boff,
+ gint m, struct _ctx *ctx)
+{
+ struct middle_snake ms;
+ gint d;
+
+ if (n == 0) {
+ _edit (ctx, DIFF_INSERT, boff, m);
+ d = m;
+ }
+ else if (m == 0) {
+ _edit (ctx, DIFF_DELETE, aoff, n);
+ d = n;
+ }
+ else {
+ /* Find the middle "snake" around which we
+ * recursively solve the sub-problems.
+ */
+ d = _find_middle_snake (a, aoff, n, b, boff, m, ctx, &ms);
+ if (d == -1) {
+ return -1;
+ }
+ else if (d >= ctx->dmax) {
+ return ctx->dmax;
+ }
+ else if (ctx->ses == NULL) {
+ return d;
+ }
+ else if (d > 1) {
+ if (_ses (a, aoff, ms.x, b, boff, ms.y, ctx) == -1) {
+ return -1;
+ }
+
+ _edit (ctx, DIFF_MATCH, aoff + ms.x, ms.u - ms.x);
+
+ aoff += ms.u;
+ boff += ms.v;
+ n -= ms.u;
+ m -= ms.v;
+ if (_ses (a, aoff, n, b, boff, m, ctx) == -1) {
+ return -1;
+ }
+ }
+ else {
+ gint x = ms.x;
+ gint u = ms.u;
+
+ /* There are only 4 base cases when the
+ * edit distance is 1.
+ *
+ * n > m m > n
+ *
+ * - |
+ * \ \ x != u
+ * \ \
+ *
+ * \ \
+ * \ \ x == u
+ * - |
+ */
+
+ if (m > n) {
+ if (x == u) {
+ _edit (ctx, DIFF_MATCH, aoff, n);
+ _edit (ctx, DIFF_INSERT, boff + (m - 1), 1);
+ }
+ else {
+ _edit (ctx, DIFF_INSERT, boff, 1);
+ _edit (ctx, DIFF_MATCH, aoff, n);
+ }
+ }
+ else {
+ if (x == u) {
+ _edit (ctx, DIFF_MATCH, aoff, m);
+ _edit (ctx, DIFF_DELETE, aoff + (n - 1), 1);
+ }
+ else {
+ _edit (ctx, DIFF_DELETE, aoff, 1);
+ _edit (ctx, DIFF_MATCH, aoff + 1, m);
+ }
+ }
+ }
+ }
+
+ return d;
+}
+
+gint
+rspamd_diff(const void *a, gint aoff, gint n, const void *b, gint boff, gint m,
+ gint dmax, GArray *ses, gint *sn)
+{
+ struct _ctx ctx;
+ gint d, x, y;
+ struct diff_edit *e = NULL;
+ GArray *tmp;
+
+ tmp = g_array_sized_new (FALSE, TRUE, sizeof(gint), dmax);
+ ctx.buf = tmp;
+ ctx.ses = ses;
+ ctx.si = 0;
+ ctx.dmax = dmax;
+
+ /* The _ses function assumes the SES will begin or end with a delete
+ * or insert. The following will insure this is true by eating any
+ * beginning matches. This is also a quick to process sequences
+ * that match entirely.
+ */
+ x = y = 0;
+ const guchar *a0 = (const guchar *) a + aoff;
+ const guchar *b0 = (const guchar *) b + boff;
+ while (x < n && y < m && a0[x] == b0[y]) {
+ x++;
+ y++;
+ }
+ _edit (&ctx, DIFF_MATCH, aoff, x);
+
+ if ((d = _ses (a, aoff + x, n - x, b, boff + y, m - y, &ctx)) == -1) {
+ g_array_free (tmp, TRUE);
+ return -1;
+ }
+ if (ses && sn) {
+ *sn = e->op ? ctx.si + 1 : 0;
+ }
+
+ g_array_free (tmp, TRUE);
+ return d;
+}
+
+guint32
+compare_diff_distance (f_str_t *s1, f_str_t *s2)
+{
+ GArray *ses;
+ struct diff_edit *e;
+ gint i;
+ guint32 distance = 0;
+
+ ses = g_array_sized_new (FALSE, TRUE, sizeof (struct diff_edit), MAX_DIFF);
+
+ if (rspamd_diff (s1->begin, 0, s1->len,
+ s2->begin, 0, s2->len, MAX_DIFF, ses, NULL) == -1) {
+ /* Diff failed, strings are different */
+ g_array_free (ses, TRUE);
+ return 0;
+ }
+
+ for (i = 0; i < ses->len; i ++) {
+ e = &g_array_index(ses, struct diff_edit, i);
+ if (e->op != DIFF_MATCH) {
+ distance += e->len;
+ }
+ }
+
+ g_array_free (ses, TRUE);
+ return 100 - (2 * distance * 100) / (s1->len + s2->len);
+}
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