13 files changed, 586 insertions, 25 deletions

diff --git a/Makefile b/Makefile
index 4e101d3..f8a4d47 100644
--- a/Makefile
+++ b/Makefile
@@ -93,6 +93,7 @@ OBJECTS += ui-refs.o
 OBJECTS += ui-repolist.o
 OBJECTS += ui-shared.o
 OBJECTS += ui-snapshot.o
+OBJECTS += ui-ssdiff.o
 OBJECTS += ui-stats.o
 OBJECTS += ui-summary.o
 OBJECTS += ui-tag.o
diff --git a/cgit.c b/cgit.c
index 08cb5d2..4f68a4b 100644
--- a/cgit.c
+++ b/cgit.c
@@ -184,6 +184,8 @@ void config_cb(const char *name, const char *value)
 		ctx.cfg.summary_branches = atoi(value);
 	else if (!strcmp(name, "summary-tags"))
 		ctx.cfg.summary_tags = atoi(value);
+	else if (!strcmp(name, "side-by-side-diffs"))
+		ctx.cfg.ssdiff = atoi(value);
 	else if (!strcmp(name, "agefile"))
 		ctx.cfg.agefile = xstrdup(value);
 	else if (!strcmp(name, "renamelimit"))
@@ -242,6 +244,8 @@ static void querystring_cb(const char *name, const char *value)
 		ctx.qry.showmsg = atoi(value);
 	} else if (!strcmp(name, "period")) {
 		ctx.qry.period = xstrdup(value);
+	} else if (!strcmp(name, "ss")) {
+		ctx.qry.ssdiff = atoi(value);
 	}
 }
 
@@ -284,6 +288,7 @@ static void prepare_context(struct cgit_context *ctx)
 	ctx->cfg.summary_branches = 10;
 	ctx->cfg.summary_log = 10;
 	ctx->cfg.summary_tags = 10;
+	ctx->cfg.ssdiff = 0;
 	ctx->env.cgit_config = xstrdupn(getenv("CGIT_CONFIG"));
 	ctx->env.http_host = xstrdupn(getenv("HTTP_HOST"));
 	ctx->env.https = xstrdupn(getenv("HTTPS"));
diff --git a/cgit.css b/cgit.css
index ef7d3c1..0cb894a 100644
--- a/cgit.css
+++ b/cgit.css
@@ -606,3 +606,102 @@ table.hgraph div.bar {
 	background-color: #eee;
 	height: 1em;
 }
+
+table.ssdiff {
+	width: 100%;
+}
+
+table.ssdiff td {
+	font-size: 75%;
+	font-family: monospace;
+	white-space: pre;
+	padding: 1px 4px 1px 4px;
+	border-left: solid 1px #aaa;
+	border-right: solid 1px #aaa;
+}
+
+table.ssdiff td.add {
+	color: black;
+	background: #cfc;
+	min-width: 50%;
+}
+
+table.ssdiff td.add_dark {
+	color: black;
+	background: #aca;
+	min-width: 50%;
+}
+
+table.ssdiff span.add {
+	background: #cfc;
+	font-weight: bold;
+}
+
+table.ssdiff td.del {
+	color: black;
+	background: #fcc;
+	min-width: 50%;
+}
+
+table.ssdiff td.del_dark {
+	color: black;
+	background: #caa;
+	min-width: 50%;
+}
+
+table.ssdiff span.del {
+	background: #fcc;
+	font-weight: bold;
+}
+
+table.ssdiff td.changed {
+	color: black;
+	background: #ffc;
+	min-width: 50%;
+}
+
+table.ssdiff td.changed_dark {
+	color: black;
+	background: #cca;
+	min-width: 50%;
+}
+
+table.ssdiff td.lineno {
+	color: black;
+	background: #eee;
+	text-align: right;
+	width: 3em;
+	min-width: 3em;
+}
+
+table.ssdiff td.hunk {
+	color: #black;
+	background: #ccf;
+	border-top: solid 1px #aaa;
+	border-bottom: solid 1px #aaa;
+}
+
+table.ssdiff td.head {
+	border-top: solid 1px #aaa;
+	border-bottom: solid 1px #aaa;
+}
+
+table.ssdiff td.head div.head {
+	font-weight: bold;
+	color: black;
+}
+
+table.ssdiff td.foot {
+	border-top: solid 1px #aaa;
+        border-left: none;
+        border-right: none;
+        border-bottom: none;
+}
+
+table.ssdiff td.space {
+	border: none;
+}
+
+table.ssdiff td.space div {
+	min-height: 3em;
+}
\ No newline at end of file
diff --git a/cgit.h b/cgit.h
index 39853df..5941ec0 100644
--- a/cgit.h
+++ b/cgit.h
@@ -143,6 +143,7 @@ struct cgit_query {
 	int nohead;
 	char *sort;
 	int showmsg;
+	int ssdiff;
 };
 
 struct cgit_config {
@@ -195,6 +196,7 @@ struct cgit_config {
 	int summary_branches;
 	int summary_log;
 	int summary_tags;
+	int ssdiff;
 	struct string_list mimetypes;
 	struct cgit_filter *about_filter;
 	struct cgit_filter *commit_filter;
diff --git a/cgitrc.5.txt b/cgitrc.5.txt
index e69140b..70e4c78 100644
--- a/cgitrc.5.txt
+++ b/cgitrc.5.txt
@@ -245,6 +245,10 @@ section::
 	after this option will inherit the current section name. Default value:
 	none.
 
+side-by-side-diffs::
+	If set to "1" shows side-by-side diffs instead of unidiffs per
+	default. Default value: "0".
+
 snapshots::
 	Text which specifies the default set of snapshot formats generated by
 	cgit. The value is a space-separated list of zero or more of the
diff --git a/ui-commit.c b/ui-commit.c
index f5b0ae5..b5e3c01 100644
--- a/ui-commit.c
+++ b/ui-commit.c
@@ -58,9 +58,14 @@ void cgit_print_commit(char *hex)
 	html("</td></tr>\n");
 	html("<tr><th>commit</th><td colspan='2' class='sha1'>");
 	tmp = sha1_to_hex(commit->object.sha1);
-	cgit_commit_link(tmp, NULL, NULL, ctx.qry.head, tmp);
+	cgit_commit_link(tmp, NULL, NULL, ctx.qry.head, tmp, 0);
 	html(" (");
 	cgit_patch_link("patch", NULL, NULL, NULL, tmp);
+	html(") (");
+	if ((ctx.qry.ssdiff && !ctx.cfg.ssdiff) || (!ctx.qry.ssdiff && ctx.cfg.ssdiff))
+		cgit_commit_link("unidiff", NULL, NULL, ctx.qry.head, tmp, 1);
+	else
+		cgit_commit_link("side-by-side diff", NULL, NULL, ctx.qry.head, tmp, 1);
 	html(")</td></tr>\n");
 	html("<tr><th>tree</th><td colspan='2' class='sha1'>");
 	tmp = xstrdup(hex);
@@ -78,10 +83,10 @@ void cgit_print_commit(char *hex)
 		html("<tr><th>parent</th>"
 		     "<td colspan='2' class='sha1'>");
 		cgit_commit_link(sha1_to_hex(p->item->object.sha1), NULL, NULL,
-				 ctx.qry.head, sha1_to_hex(p->item->object.sha1));
+				 ctx.qry.head, sha1_to_hex(p->item->object.sha1), 0);
 		html(" (");
 		cgit_diff_link("diff", NULL, NULL, ctx.qry.head, hex,
-			       sha1_to_hex(p->item->object.sha1), NULL);
+			       sha1_to_hex(p->item->object.sha1), NULL, 0);
 		html(")</td></tr>");
 		parents++;
 	}
diff --git a/ui-diff.c b/ui-diff.c
index 2196745..a92a768 100644
--- a/ui-diff.c
+++ b/ui-diff.c
@@ -9,6 +9,7 @@
 #include "cgit.h"
 #include "html.h"
 #include "ui-shared.h"
+#include "ui-ssdiff.h"
 
 unsigned char old_rev_sha1[20];
 unsigned char new_rev_sha1[20];
@@ -32,6 +33,7 @@ static struct fileinfo {
 	int binary:1;
 } *items;
 
+static int use_ssdiff = 0;
 
 static void print_fileinfo(struct fileinfo *info)
 {
@@ -83,7 +85,7 @@ static void print_fileinfo(struct fileinfo *info)
 	}
 	htmlf("</td><td class='%s'>", class);
 	cgit_diff_link(info->new_path, NULL, NULL, ctx.qry.head, ctx.qry.sha1,
-		       ctx.qry.sha2, info->new_path);
+		       ctx.qry.sha2, info->new_path, 0);
 	if (info->status == DIFF_STATUS_COPIED || info->status == DIFF_STATUS_RENAMED)
 		htmlf(" (%s from %s)",
 		      info->status == DIFF_STATUS_COPIED ? "copied" : "renamed",
@@ -158,7 +160,7 @@ void cgit_print_diffstat(const unsigned char *old_sha1,
 
 	html("<div class='diffstat-header'>");
 	cgit_diff_link("Diffstat", NULL, NULL, ctx.qry.head, ctx.qry.sha1,
-		       ctx.qry.sha2, NULL);
+		       ctx.qry.sha2, NULL, 0);
 	html("</div>");
 	html("<table summary='diffstat' class='diffstat'>");
 	max_changes = 0;
@@ -246,26 +248,54 @@ static void header(unsigned char *sha1, char *path1, int mode1,
 	html("</div>");
 }
 
+static void print_ssdiff_link()
+{
+	if (!strcmp(ctx.qry.page, "diff")) {
+		if (use_ssdiff)
+			cgit_diff_link("Unidiff", NULL, NULL, ctx.qry.head,
+				       ctx.qry.sha1, ctx.qry.sha2, ctx.qry.path, 1);
+		else
+			cgit_diff_link("Side-by-side diff", NULL, NULL,
+				       ctx.qry.head, ctx.qry.sha1,
+				       ctx.qry.sha2, ctx.qry.path, 1);
+	}
+}
+
 static void filepair_cb(struct diff_filepair *pair)
 {
 	unsigned long old_size = 0;
 	unsigned long new_size = 0;
 	int binary = 0;
+	linediff_fn print_line_fn = print_line;
 
+	if (use_ssdiff) {
+		cgit_ssdiff_header_begin();
+		print_line_fn = cgit_ssdiff_line_cb;
+	}
 	header(pair->one->sha1, pair->one->path, pair->one->mode,
 	       pair->two->sha1, pair->two->path, pair->two->mode);
+	if (use_ssdiff)
+		cgit_ssdiff_header_end();
 	if (S_ISGITLINK(pair->one->mode) || S_ISGITLINK(pair->two->mode)) {
 		if (S_ISGITLINK(pair->one->mode))
-			print_line(fmt("-Subproject %s", sha1_to_hex(pair->one->sha1)), 52);
+			print_line_fn(fmt("-Subproject %s", sha1_to_hex(pair->one->sha1)), 52);
 		if (S_ISGITLINK(pair->two->mode))
-			print_line(fmt("+Subproject %s", sha1_to_hex(pair->two->sha1)), 52);
+			print_line_fn(fmt("+Subproject %s", sha1_to_hex(pair->two->sha1)), 52);
+		if (use_ssdiff)
+			cgit_ssdiff_footer();
 		return;
 	}
-	if (cgit_diff_files(pair->one->sha1, pair->two->sha1, &old_size, 
-			    &new_size, &binary, print_line))
+	if (cgit_diff_files(pair->one->sha1, pair->two->sha1, &old_size,
+			    &new_size, &binary, print_line_fn))
 		cgit_print_error("Error running diff");
-	if (binary)
-		html("Binary files differ");
+	if (binary) {
+		if (use_ssdiff)
+			html("<tr><td colspan='4'>Binary files differ</td></tr>");
+		else
+			html("Binary files differ");
+	}
+	if (use_ssdiff)
+		cgit_ssdiff_footer();
 }
 
 void cgit_print_diff(const char *new_rev, const char *old_rev, const char *prefix)
@@ -303,11 +333,21 @@ void cgit_print_diff(const char *new_rev, const char *old_rev, const char *prefi
 		if (!commit2 || parse_commit(commit2))
 			cgit_print_error(fmt("Bad commit: %s", sha1_to_hex(old_rev_sha1)));
 	}
+
+	if ((ctx.qry.ssdiff && !ctx.cfg.ssdiff) || (!ctx.qry.ssdiff && ctx.cfg.ssdiff))
+		use_ssdiff = 1;
+
+	print_ssdiff_link();
 	cgit_print_diffstat(old_rev_sha1, new_rev_sha1);
 
-	html("<table summary='diff' class='diff'>");
-	html("<tr><td>");
+	if (use_ssdiff) {
+		html("<table summary='ssdiff' class='ssdiff'>");
+	} else {
+		html("<table summary='diff' class='diff'>");
+		html("<tr><td>");
+	}
 	cgit_diff_tree(old_rev_sha1, new_rev_sha1, filepair_cb, prefix);
-	html("</td></tr>");
+	if (!use_ssdiff)
+		html("</td></tr>");
 	html("</table>");
 }
diff --git a/ui-log.c b/ui-log.c
index f3132c9..0947604 100644
--- a/ui-log.c
+++ b/ui-log.c
@@ -66,7 +66,7 @@ void show_commit_decorations(struct commit *commit)
 		else {
 			strncpy(buf, deco->name, sizeof(buf) - 1);
 			cgit_commit_link(buf, NULL, "deco", ctx.qry.head,
-				sha1_to_hex(commit->object.sha1));
+				sha1_to_hex(commit->object.sha1), 0);
 		}
 		deco = deco->next;
 	}
@@ -89,7 +89,7 @@ void print_commit(struct commit *commit)
 	htmlf("</td><td%s>",
 		ctx.qry.showmsg ? " class='logsubject'" : "");
 	cgit_commit_link(info->subject, NULL, NULL, ctx.qry.head,
-			 sha1_to_hex(commit->object.sha1));
+			 sha1_to_hex(commit->object.sha1), 0);
 	show_commit_decorations(commit);
 	html("</td><td>");
 	html_txt(info->author);
diff --git a/ui-refs.c b/ui-refs.c
index d3b4f6e..33d9bec 100644
--- a/ui-refs.c
+++ b/ui-refs.c
@@ -74,7 +74,7 @@ static int print_branch(struct refinfo *ref)
 	html("</td><td>");
 
 	if (ref->object->type == OBJ_COMMIT) {
-		cgit_commit_link(info->subject, NULL, NULL, name, NULL);
+		cgit_commit_link(info->subject, NULL, NULL, name, NULL, 0);
 		html("</td><td>");
 		html_txt(info->author);
 		html("</td><td colspan='2'>");
diff --git a/ui-shared.c b/ui-shared.c
index 3a9e67b..08ea003 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -317,7 +317,7 @@ void cgit_log_link(char *name, char *title, char *class, char *head,
 }
 
 void cgit_commit_link(char *name, char *title, char *class, char *head,
-		      char *rev)
+		      char *rev, int toggle_ssdiff)
 {
 	if (strlen(name) > ctx.cfg.max_msg_len && ctx.cfg.max_msg_len >= 15) {
 		name[ctx.cfg.max_msg_len] = '\0';
@@ -325,7 +325,23 @@ void cgit_commit_link(char *name, char *title, char *class, char *head,
 		name[ctx.cfg.max_msg_len - 2] = '.';
 		name[ctx.cfg.max_msg_len - 3] = '.';
 	}
-	reporevlink("commit", name, title, class, head, rev, NULL);
+
+	char *delim;
+
+	delim = repolink(title, class, "commit", head, NULL);
+	if (rev && strcmp(rev, ctx.qry.head)) {
+		html(delim);
+		html("id=");
+		html_url_arg(rev);
+		delim = "&amp;";
+	}
+	if ((ctx.qry.ssdiff && !toggle_ssdiff) || (!ctx.qry.ssdiff && toggle_ssdiff)) {
+		html(delim);
+		html("ss=1");
+	}
+	html("'>");
+	html_txt(name);
+	html("</a>");
 }
 
 void cgit_refs_link(char *name, char *title, char *class, char *head,
@@ -341,7 +357,8 @@ void cgit_snapshot_link(char *name, char *title, char *class, char *head,
 }
 
 void cgit_diff_link(char *name, char *title, char *class, char *head,
-		    char *new_rev, char *old_rev, char *path)
+		    char *new_rev, char *old_rev, char *path,
+		    int toggle_ssdiff)
 {
 	char *delim;
 
@@ -356,6 +373,11 @@ void cgit_diff_link(char *name, char *title, char *class, char *head,
 		html(delim);
 		html("id2=");
 		html_url_arg(old_rev);
+		delim = "&amp;";
+	}
+	if ((ctx.qry.ssdiff && !toggle_ssdiff) || (!ctx.qry.ssdiff && toggle_ssdiff)) {
+		html(delim);
+		html("ss=1");
 	}
 	html("'>");
 	html_txt(name);
@@ -383,7 +405,7 @@ void cgit_object_link(struct object *obj)
 	shortrev[10] = '\0';
 	if (obj->type == OBJ_COMMIT) {
                 cgit_commit_link(fmt("commit %s...", shortrev), NULL, NULL,
-				 ctx.qry.head, fullrev);
+				 ctx.qry.head, fullrev, 0);
 		return;
 	} else if (obj->type == OBJ_TREE)
 		page = "tree";
@@ -695,9 +717,9 @@ void cgit_print_pageheader(struct cgit_context *ctx)
 		cgit_tree_link("tree", NULL, hc(cmd, "tree"), ctx->qry.head,
 			       ctx->qry.sha1, NULL);
 		cgit_commit_link("commit", NULL, hc(cmd, "commit"),
-				 ctx->qry.head, ctx->qry.sha1);
+				 ctx->qry.head, ctx->qry.sha1, 0);
 		cgit_diff_link("diff", NULL, hc(cmd, "diff"), ctx->qry.head,
-			       ctx->qry.sha1, ctx->qry.sha2, NULL);
+			       ctx->qry.sha1, ctx->qry.sha2, NULL, 0);
 		if (ctx->repo->max_stats)
 			cgit_stats_link("stats", NULL, hc(cmd, "stats"),
 					ctx->qry.head, NULL);
diff --git a/ui-shared.h b/ui-shared.h
index b12aa89..9ebc1f9 100644
--- a/ui-shared.h
+++ b/ui-shared.h
@@ -23,7 +23,7 @@ extern void cgit_log_link(char *name, char *title, char *class, char *head,
 			  char *rev, char *path, int ofs, char *grep,
 			  char *pattern, int showmsg);
 extern void cgit_commit_link(char *name, char *title, char *class, char *head,
-			     char *rev);
+			     char *rev, int toggle_ssdiff);
 extern void cgit_patch_link(char *name, char *title, char *class, char *head,
 			    char *rev);
 extern void cgit_refs_link(char *name, char *title, char *class, char *head,
@@ -31,7 +31,8 @@ extern void cgit_refs_link(char *name, char *title, char *class, char *head,
 extern void cgit_snapshot_link(char *name, char *title, char *class,
 			       char *head, char *rev, char *archivename);
 extern void cgit_diff_link(char *name, char *title, char *class, char *head,
-			   char *new_rev, char *old_rev, char *path);
+			   char *new_rev, char *old_rev, char *path,
+			   int toggle_ssdiff);
 extern void cgit_stats_link(char *name, char *title, char *class, char *head,
 			    char *path);
 extern void cgit_object_link(struct object *obj);
diff --git a/ui-ssdiff.c b/ui-ssdiff.c
new file mode 100644
index 0000000..408e620
--- /dev/null
+++ b/ui-ssdiff.c
@@ -0,0 +1,369 @@
+#include "cgit.h"
+#include "html.h"
+#include "ui-shared.h"
+
+extern int use_ssdiff;
+
+static int current_old_line, current_new_line;
+
+struct deferred_lines {
+	int line_no;
+	char *line;
+	struct deferred_lines *next;
+};
+
+static struct deferred_lines *deferred_old, *deferred_old_last;
+static struct deferred_lines *deferred_new, *deferred_new_last;
+
+static char *longest_common_subsequence(char *A, char *B)
+{
+	int i, j, ri;
+	int m = strlen(A);
+	int n = strlen(B);
+	int L[m + 1][n + 1];
+	int tmp1, tmp2;
+	int lcs_length;
+	char *result;
+
+	for (i = m; i >= 0; i--) {
+		for (j = n; j >= 0; j--) {
+			if (A[i] == '\0' || B[j] == '\0') {
+				L[i][j] = 0;
+			} else if (A[i] == B[j]) {
+				L[i][j] = 1 + L[i + 1][j + 1];
+			} else {
+				tmp1 = L[i + 1][j];
+				tmp2 = L[i][j + 1];
+				L[i][j] = (tmp1 > tmp2 ? tmp1 : tmp2);
+			}
+		}
+	}
+
+	lcs_length = L[0][0];
+	result = xmalloc(lcs_length + 2);
+	memset(result, 0, sizeof(*result) * (lcs_length + 2));
+
+	ri = 0;
+	i = 0;
+	j = 0;
+	while (i < m && j < n) {
+		if (A[i] == B[j]) {
+			result[ri] = A[i];
+			ri += 1;
+			i += 1;
+			j += 1;
+		} else if (L[i + 1][j] >= L[i][j + 1]) {
+			i += 1;
+		} else {
+			j += 1;
+		}
+	}
+	return result;
+}
+
+static int line_from_hunk(char *line, char type)
+{
+	char *buf1, *buf2;
+	int len;
+
+	buf1 = strchr(line, type);
+	if (buf1 == NULL)
+		return 0;
+	buf1 += 1;
+	buf2 = strchr(buf1, ',');
+	if (buf2 == NULL)
+		return 0;
+	len = buf2 - buf1;
+	buf2 = xmalloc(len + 1);
+	strncpy(buf2, buf1, len);
+	buf2[len] = '\0';
+	int res = atoi(buf2);
+	free(buf2);
+	return res;
+}
+
+static char *replace_tabs(char *line)
+{
+	char *prev_buf = line;
+	char *cur_buf;
+	int linelen = strlen(line);
+	int n_tabs = 0;
+	int i;
+	char *result;
+	char *spaces = "        ";
+
+	if (linelen == 0) {
+		result = xmalloc(1);
+		result[0] = '\0';
+		return result;
+	}
+
+	for (i = 0; i < linelen; i++)
+		if (line[i] == '\t')
+			n_tabs += 1;
+	result = xmalloc(linelen + n_tabs * 8 + 1);
+	result[0] = '\0';
+
+	while (1) {
+		cur_buf = strchr(prev_buf, '\t');
+		if (!cur_buf) {
+			strcat(result, prev_buf);
+			break;
+		} else {
+			strcat(result, " ");
+			strncat(result, spaces, 8 - (strlen(result) % 8));
+			strncat(result, prev_buf, cur_buf - prev_buf);
+		}
+		prev_buf = cur_buf + 1;
+	}
+	return result;
+}
+
+static int calc_deferred_lines(struct deferred_lines *start)
+{
+	struct deferred_lines *item = start;
+	int result = 0;
+	while (item) {
+		result += 1;
+		item = item->next;
+	}
+	return result;
+}
+
+static void deferred_old_add(char *line, int line_no)
+{
+	struct deferred_lines *item = xmalloc(sizeof(struct deferred_lines));
+	item->line = xstrdup(line);
+	item->line_no = line_no;
+	item->next = NULL;
+	if (deferred_old) {
+		deferred_old_last->next = item;
+		deferred_old_last = item;
+	} else {
+		deferred_old = deferred_old_last = item;
+	}
+}
+
+static void deferred_new_add(char *line, int line_no)
+{
+	struct deferred_lines *item = xmalloc(sizeof(struct deferred_lines));
+	item->line = xstrdup(line);
+	item->line_no = line_no;
+	item->next = NULL;
+	if (deferred_new) {
+		deferred_new_last->next = item;
+		deferred_new_last = item;
+	} else {
+		deferred_new = deferred_new_last = item;
+	}
+}
+
+static void print_part_with_lcs(char *class, char *line, char *lcs)
+{
+	int line_len = strlen(line);
+	int i, j;
+	char c[2] = " ";
+	int same = 1;
+
+	j = 0;
+	for (i = 0; i < line_len; i++) {
+		c[0] = line[i];
+		if (same) {
+			if (line[i] == lcs[j])
+				j += 1;
+			else {
+				same = 0;
+				htmlf("<span class='%s'>", class);
+			}
+		} else if (line[i] == lcs[j]) {
+			same = 1;
+			htmlf("</span>");
+			j += 1;
+		}
+		html_txt(c);
+	}
+}
+
+static void print_ssdiff_line(char *class,
+			      int old_line_no,
+			      char *old_line,
+			      int new_line_no,
+			      char *new_line, int individual_chars)
+{
+	char *lcs = NULL;
+	if (old_line)
+		old_line = replace_tabs(old_line + 1);
+	if (new_line)
+		new_line = replace_tabs(new_line + 1);
+	if (individual_chars && old_line && new_line)
+		lcs = longest_common_subsequence(old_line, new_line);
+	html("<tr>");
+	if (old_line_no > 0)
+		htmlf("<td class='lineno'>%d</td><td class='%s'>",
+		      old_line_no, class);
+	else if (old_line)
+		htmlf("<td class='lineno'></td><td class='%s'>", class);
+	else
+		htmlf("<td class='lineno'></td><td class='%s_dark'>", class);
+	if (old_line) {
+		if (lcs)
+			print_part_with_lcs("del", old_line, lcs);
+		else
+			html_txt(old_line);
+	}
+
+	html("</td>");
+	if (new_line_no > 0)
+		htmlf("<td class='lineno'>%d</td><td class='%s'>",
+		      new_line_no, class);
+	else if (new_line)
+		htmlf("<td class='lineno'></td><td class='%s'>", class);
+	else
+		htmlf("<td class='lineno'></td><td class='%s_dark'>", class);
+	if (new_line) {
+		if (lcs)
+			print_part_with_lcs("add", new_line, lcs);
+		else
+			html_txt(new_line);
+	}
+
+	html("</td></tr>");
+	if (lcs)
+		free(lcs);
+	if (new_line)
+		free(new_line);
+	if (old_line)
+		free(old_line);
+}
+
+static void print_deferred_old_lines()
+{
+	struct deferred_lines *iter_old, *tmp;
+	iter_old = deferred_old;
+	while (iter_old) {
+		print_ssdiff_line("del", iter_old->line_no,
+				  iter_old->line, -1, NULL, 0);
+		tmp = iter_old->next;
+		free(iter_old);
+		iter_old = tmp;
+	}
+}
+
+static void print_deferred_new_lines()
+{
+	struct deferred_lines *iter_new, *tmp;
+	iter_new = deferred_new;
+	while (iter_new) {
+		print_ssdiff_line("add", -1, NULL,
+				  iter_new->line_no, iter_new->line, 0);
+		tmp = iter_new->next;
+		free(iter_new);
+		iter_new = tmp;
+	}
+}
+
+static void print_deferred_changed_lines()
+{
+	struct deferred_lines *iter_old, *iter_new, *tmp;
+	int n_old_lines = calc_deferred_lines(deferred_old);
+	int n_new_lines = calc_deferred_lines(deferred_new);
+	int individual_chars = (n_old_lines == n_new_lines ? 1 : 0);
+
+	iter_old = deferred_old;
+	iter_new = deferred_new;
+	while (iter_old || iter_new) {
+		if (iter_old && iter_new)
+			print_ssdiff_line("changed", iter_old->line_no,
+					  iter_old->line,
+					  iter_new->line_no, iter_new->line,
+					  individual_chars);
+		else if (iter_old)
+			print_ssdiff_line("changed", iter_old->line_no,
+					  iter_old->line, -1, NULL, 0);
+		else if (iter_new)
+			print_ssdiff_line("changed", -1, NULL,
+					  iter_new->line_no, iter_new->line, 0);
+		if (iter_old) {
+			tmp = iter_old->next;
+			free(iter_old);
+			iter_old = tmp;
+		}
+
+		if (iter_new) {
+			tmp = iter_new->next;
+			free(iter_new);
+			iter_new = tmp;
+		}
+	}
+}
+
+void cgit_ssdiff_print_deferred_lines()
+{
+	if (!deferred_old && !deferred_new)
+		return;
+	if (deferred_old && !deferred_new)
+		print_deferred_old_lines();
+	else if (!deferred_old && deferred_new)
+		print_deferred_new_lines();
+	else
+		print_deferred_changed_lines();
+	deferred_old = deferred_old_last = NULL;
+	deferred_new = deferred_new_last = NULL;
+}
+
+/*
+ * print a single line returned from xdiff
+ */
+void cgit_ssdiff_line_cb(char *line, int len)
+{
+	char c = line[len - 1];
+	line[len - 1] = '\0';
+	if (line[0] == '@') {
+		current_old_line = line_from_hunk(line, '-');
+		current_new_line = line_from_hunk(line, '+');
+	}
+
+	if (line[0] == ' ') {
+		if (deferred_old || deferred_new)
+			cgit_ssdiff_print_deferred_lines();
+		print_ssdiff_line("ctx", current_old_line, line,
+				  current_new_line, line, 0);
+		current_old_line += 1;
+		current_new_line += 1;
+	} else if (line[0] == '+') {
+		deferred_new_add(line, current_new_line);
+		current_new_line += 1;
+	} else if (line[0] == '-') {
+		deferred_old_add(line, current_old_line);
+		current_old_line += 1;
+	} else if (line[0] == '@') {
+		html("<tr><td colspan='4' class='hunk'>");
+		html_txt(line);
+		html("</td></tr>");
+	} else {
+		html("<tr><td colspan='4' class='ctx'>");
+		html_txt(line);
+		html("</td></tr>");
+	}
+	line[len - 1] = c;
+}
+
+void cgit_ssdiff_header_begin()
+{
+	current_old_line = -1;
+	current_new_line = -1;
+	html("<tr><td class='space' colspan='4'><div></div></td></tr>");
+	html("<tr><td class='head' colspan='4'>");
+}
+
+void cgit_ssdiff_header_end()
+{
+	html("</td><tr>");
+}
+
+void cgit_ssdiff_footer()
+{
+	if (deferred_old || deferred_new)
+		cgit_ssdiff_print_deferred_lines();
+	html("<tr><td class='foot' colspan='4'></td></tr>");
+}
diff --git a/ui-ssdiff.h b/ui-ssdiff.h
new file mode 100644
index 0000000..64b4b12
--- /dev/null
+++ b/ui-ssdiff.h
@@ -0,0 +1,13 @@
+#ifndef UI_SSDIFF_H
+#define UI_SSDIFF_H
+
+extern void cgit_ssdiff_print_deferred_lines();
+
+extern void cgit_ssdiff_line_cb(char *line, int len);
+
+extern void cgit_ssdiff_header_begin();
+extern void cgit_ssdiff_header_end();
+
+extern void cgit_ssdiff_footer();
+
+#endif /* UI_SSDIFF_H */