13 files changed, 586 insertions, 25 deletions

diff --git a/Makefile b/Makefile
index 4e101d3..f8a4d47 100644
--- a/Makefile
+++ b/Makefile
@@ -84,24 +84,25 @@ OBJECTS += shared.o
 OBJECTS += ui-atom.o
 OBJECTS += ui-blob.o
 OBJECTS += ui-clone.o
 OBJECTS += ui-commit.o
 OBJECTS += ui-diff.o
 OBJECTS += ui-log.o
 OBJECTS += ui-patch.o
 OBJECTS += ui-plain.o
 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
 OBJECTS += ui-tree.o
 
 ifdef NEEDS_LIBICONV
         EXTLIBS += -liconv
 endif
 
 
 .PHONY: all libgit test install uninstall clean force-version get-git \
         doc man-doc html-doc clean-doc
diff --git a/cgit.c b/cgit.c
index 08cb5d2..4f68a4b 100644
--- a/cgit.c
+++ b/cgit.c
@@ -175,24 +175,26 @@ void config_cb(const char *name, const char *value)
                 if (!ctx.cfg.nocache && ctx.cfg.cache_size)
                         process_cached_repolist(value);
                 else
                         scan_tree(value, repo_config);
         else if (!strcmp(name, "source-filter"))
                 ctx.cfg.source_filter = new_filter(value, 1);
         else if (!strcmp(name, "summary-log"))
                 ctx.cfg.summary_log = atoi(value);
         else if (!strcmp(name, "summary-branches"))
                 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"))
                 ctx.cfg.renamelimit = atoi(value);
         else if (!strcmp(name, "robots"))
                 ctx.cfg.robots = xstrdup(value);
         else if (!strcmp(name, "clone-prefix"))
                 ctx.cfg.clone_prefix = xstrdup(value);
         else if (!strcmp(name, "local-time"))
                 ctx.cfg.local_time = atoi(value);
         else if (!prefixcmp(name, "mimetype."))
                 add_mimetype(name + 9, value);
@@ -233,24 +235,26 @@ static void querystring_cb(const char *name, const char *value)
         } else if (!strcmp(name, "path")) {
                 ctx.qry.path = trim_end(value, '/');
         } else if (!strcmp(name, "name")) {
                 ctx.qry.name = xstrdup(value);
         } else if (!strcmp(name, "mimetype")) {
                 ctx.qry.mimetype = xstrdup(value);
         } else if (!strcmp(name, "s")){
                 ctx.qry.sort = xstrdup(value);
         } else if (!strcmp(name, "showmsg")) {
                 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);
         }
 }
 
 char *xstrdupn(const char *str)
 {
         return (str ? xstrdup(str) : NULL);
 }
 
 static void prepare_context(struct cgit_context *ctx)
 {
         memset(ctx, 0, sizeof(ctx));
         ctx->cfg.agefile = "info/web/last-modified";
@@ -275,24 +279,25 @@ static void prepare_context(struct cgit_context *ctx)
         ctx->cfg.max_blob_size = 0;
         ctx->cfg.max_stats = 0;
         ctx->cfg.module_link = "./?repo=%s&page=commit&id=%s";
         ctx->cfg.renamelimit = -1;
         ctx->cfg.robots = "index, nofollow";
         ctx->cfg.root_title = "Git repository browser";
         ctx->cfg.root_desc = "a fast webinterface for the git dscm";
         ctx->cfg.script_name = CGIT_SCRIPT_NAME;
         ctx->cfg.section = "";
         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"));
         ctx->env.no_http = xstrdupn(getenv("NO_HTTP"));
         ctx->env.path_info = xstrdupn(getenv("PATH_INFO"));
         ctx->env.query_string = xstrdupn(getenv("QUERY_STRING"));
         ctx->env.request_method = xstrdupn(getenv("REQUEST_METHOD"));
         ctx->env.script_name = xstrdupn(getenv("SCRIPT_NAME"));
         ctx->env.server_name = xstrdupn(getenv("SERVER_NAME"));
         ctx->env.server_port = xstrdupn(getenv("SERVER_PORT"));
         ctx->page.mimetype = "text/html";
         ctx->page.charset = PAGE_ENCODING;
diff --git a/cgit.css b/cgit.css
index ef7d3c1..0cb894a 100644
--- a/cgit.css
+++ b/cgit.css
@@ -597,12 +597,111 @@ table.hgraph th {
         padding: 1px 0.5em;
 }
 
 table.hgraph td {
         vertical-align: center;
         padding: 2px 2px;
 }
 
 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
@@ -134,24 +134,25 @@ struct cgit_query {
         char *head;
         char *sha1;
         char *sha2;
         char *path;
         char *name;
         char *mimetype;
         char *url;
         char *period;
         int   ofs;
         int nohead;
         char *sort;
         int showmsg;
+        int ssdiff;
 };
 
 struct cgit_config {
         char *agefile;
         char *cache_root;
         char *clone_prefix;
         char *css;
         char *favicon;
         char *footer;
         char *head_include;
         char *header;
         char *index_header;
@@ -186,24 +187,25 @@ struct cgit_config {
         int max_msg_len;
         int max_repodesc_len;
         int max_blob_size;
         int max_stats;
         int nocache;
         int noplainemail;
         int noheader;
         int renamelimit;
         int snapshots;
         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;
         struct cgit_filter *source_filter;
 };
 
 struct cgit_page {
         time_t modified;
         time_t expires;
         size_t size;
         char *mimetype;
         char *charset;
diff --git a/cgitrc.5.txt b/cgitrc.5.txt
index e69140b..70e4c78 100644
--- a/cgitrc.5.txt
+++ b/cgitrc.5.txt
@@ -236,24 +236,28 @@ root-title::
         "Git Repository Browser".
 
 scan-path::
         A path which will be scanned for repositories. If caching is enabled,
         the result will be cached as a cgitrc include-file in the cache
         directory. Default value: none. See also: cache-scanrc-ttl.
 
 section::
         The name of the current repository section - all repositories defined
         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
         values "tar", "tar.gz", "tar.bz2" and "zip". Default value: none.
 
 source-filter::
         Specifies a command which will be invoked to format plaintext blobs
         in the tree view. The command will get the blob content on its STDIN
         and the name of the blob as its only command line argument. The STDOUT
         from the command will be included verbatim as the blob contents, i.e.
         this can be used to implement e.g. syntax highlighting. Default value:
         none.
diff --git a/ui-commit.c b/ui-commit.c
index f5b0ae5..b5e3c01 100644
--- a/ui-commit.c
+++ b/ui-commit.c
@@ -49,48 +49,53 @@ void cgit_print_commit(char *hex)
         html("</td></tr>\n");
         html("<tr><th>committer</th><td>");
         html_txt(info->committer);
         if (!ctx.cfg.noplainemail) {
                 html(" ");
                 html_txt(info->committer_email);
         }
         html("</td><td class='right'>");
         cgit_print_date(info->committer_date, FMT_LONGDATE, ctx.cfg.local_time);
         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);
         cgit_tree_link(sha1_to_hex(commit->tree->object.sha1), NULL, NULL,
                        ctx.qry.head, tmp, NULL);
         html("</td></tr>\n");
               for (p = commit->parents; p ; p = p->next) {
                 parent = lookup_commit_reference(p->item->object.sha1);
                 if (!parent) {
                         html("<tr><td colspan='3'>");
                         cgit_print_error("Error reading parent commit");
                         html("</td></tr>");
                         continue;
                 }
                 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++;
         }
         if (ctx.repo->snapshots) {
                 html("<tr><th>download</th><td colspan='2' class='sha1'>");
                 cgit_print_snapshot_links(ctx.qry.repo, ctx.qry.head,
                                           hex, ctx.repo->snapshots);
                 html("</td></tr>");
         }
         html("</table>\n");
         html("<div class='commit-subject'>");
         if (ctx.repo->commit_filter)
diff --git a/ui-diff.c b/ui-diff.c
index 2196745..a92a768 100644
--- a/ui-diff.c
+++ b/ui-diff.c
@@ -1,46 +1,48 @@
 /* ui-diff.c: show diff between two blobs
  *
  * Copyright (C) 2006 Lars Hjemli
  *
  * Licensed under GNU General Public License v2
  *   (see COPYING for full license text)
  */
 
 #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];
 
 static int files, slots;
 static int total_adds, total_rems, max_changes;
 static int lines_added, lines_removed;
 
 static struct fileinfo {
         char status;
         unsigned char old_sha1[20];
         unsigned char new_sha1[20];
         unsigned short old_mode;
         unsigned short new_mode;
         char *old_path;
         char *new_path;
         unsigned int added;
         unsigned int removed;
         unsigned long old_size;
         unsigned long new_size;
         int binary:1;
 } *items;
 
+static int use_ssdiff = 0;
 
 static void print_fileinfo(struct fileinfo *info)
 {
         char *class;
 
         switch (info->status) {
         case DIFF_STATUS_ADDED:
                 class = "add";
                 break;
         case DIFF_STATUS_COPIED:
                 class = "cpy";
                 break;
@@ -74,25 +76,25 @@ static void print_fileinfo(struct fileinfo *info)
                 cgit_print_filemode(info->new_mode);
         }
 
         if (info->old_mode != info->new_mode &&
             !is_null_sha1(info->old_sha1) &&
             !is_null_sha1(info->new_sha1)) {
                 html("<span class='modechange'>[");
                 cgit_print_filemode(info->old_mode);
                 html("]</span>");
         }
         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",
                       info->old_path);
         html("</td><td class='right'>");
         if (info->binary) {
                 htmlf("bin</td><td class='graph'>%d -> %d bytes",
                       info->old_size, info->new_size);
                 return;
         }
         htmlf("%d", info->added + info->removed);
         html("</td><td class='graph'>");
@@ -149,25 +151,25 @@ static void inspect_filepair(struct diff_filepair *pair)
                 max_changes = lines_added + lines_removed;
         total_adds += lines_added;
         total_rems += lines_removed;
 }
 
 void cgit_print_diffstat(const unsigned char *old_sha1,
                          const unsigned char *new_sha1)
 {
         int i;
 
         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;
         cgit_diff_tree(old_sha1, new_sha1, inspect_filepair, NULL);
         for(i = 0; i<files; i++)
                 print_fileinfo(&items[i]);
         html("</table>");
         html("<div class='diffstat-summary'>");
         htmlf("%d files changed, %d insertions, %d deletions",
               files, total_adds, total_rems);
         html("</div>");
 }
@@ -237,44 +239,72 @@ static void header(unsigned char *sha1, char *path1, int mode1,
                 else
                         html_txt(path1);
                 html("<br/>+++ b/");
                 if (mode2 != 0)
                         cgit_tree_link(path2, NULL, NULL, ctx.qry.head,
                                        sha1_to_hex(new_rev_sha1), path2);
                 else
                         html_txt(path2);
         }
         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)
 {
         enum object_type type;
         unsigned long size;
         struct commit *commit, *commit2;
 
         if (!new_rev)
                 new_rev = ctx.qry.head;
         get_sha1(new_rev, new_rev_sha1);
         type = sha1_object_info(new_rev_sha1, &size);
@@ -294,20 +324,30 @@ void cgit_print_diff(const char *new_rev, const char *old_rev, const char *prefi
                 hashclr(old_rev_sha1);
 
         if (!is_null_sha1(old_rev_sha1)) {
                 type = sha1_object_info(old_rev_sha1, &size);
                 if (type == OBJ_BAD) {
                         cgit_print_error(fmt("Bad object name: %s", sha1_to_hex(old_rev_sha1)));
                         return;
                 }
                 commit2 = lookup_commit_reference(old_rev_sha1);
                 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
@@ -57,48 +57,48 @@ void show_commit_decorations(struct commit *commit)
                         strncpy(buf, deco->name + 10, sizeof(buf) - 1);
                         cgit_tag_link(buf, NULL, "tag-deco", ctx.qry.head, buf);
                 }
                 else if (!prefixcmp(deco->name, "refs/remotes/")) {
                         strncpy(buf, deco->name + 13, sizeof(buf) - 1);
                         cgit_log_link(buf, NULL, "remote-deco", NULL,
                                 sha1_to_hex(commit->object.sha1), NULL,
                                 0, NULL, NULL, ctx.qry.showmsg);
                 }
                 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;
         }
 }
 
 void print_commit(struct commit *commit)
 {
         struct commitinfo *info;
         char *tmp;
         int cols = 2;
 
         info = cgit_parse_commit(commit);
         htmlf("<tr%s><td>",
                 ctx.qry.showmsg ? " class='logheader'" : "");
         tmp = fmt("id=%s", sha1_to_hex(commit->object.sha1));
         tmp = cgit_pageurl(ctx.repo->url, "commit", tmp);
         html_link_open(tmp, NULL, NULL);
         cgit_print_age(commit->date, TM_WEEK * 2, FMT_SHORTDATE);
         html_link_close();
         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);
         if (ctx.repo->enable_log_filecount) {
                 files = 0;
                 add_lines = 0;
                 rem_lines = 0;
                 cgit_diff_commit(commit, inspect_files);
                 html("</td><td>");
                 htmlf("%d", files);
                 if (ctx.repo->enable_log_linecount) {
                         html("</td><td>");
diff --git a/ui-refs.c b/ui-refs.c
index d3b4f6e..33d9bec 100644
--- a/ui-refs.c
+++ b/ui-refs.c
@@ -65,25 +65,25 @@ static int print_branch(struct refinfo *ref)
 {
         struct commitinfo *info = ref->commit;
         char *name = (char *)ref->refname;
 
         if (!info)
                 return 1;
         html("<tr><td>");
         cgit_log_link(name, NULL, NULL, name, NULL, NULL, 0, NULL, NULL,
                       ctx.qry.showmsg);
         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'>");
                 cgit_print_age(info->commit->date, -1, NULL);
         } else {
                 html("</td><td></td><td>");
                 cgit_object_link(ref->object);
         }
         html("</td></tr>\n");
         return 0;
 }
 
diff --git a/ui-shared.c b/ui-shared.c
index 3a9e67b..08ea003 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -308,63 +308,85 @@ void cgit_log_link(char *name, char *title, char *class, char *head,
                 delim = "&";
         }
         if (showmsg) {
                 html(delim);
                 html("showmsg=1");
         }
         html("'>");
         html_txt(name);
         html("</a>");
 }
 
 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';
                 name[ctx.cfg.max_msg_len - 1] = '.';
                 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,
                     char *rev, char *path)
 {
         reporevlink("refs", name, title, class, head, rev, path);
 }
 
 void cgit_snapshot_link(char *name, char *title, char *class, char *head,
                         char *rev, char *archivename)
 {
         reporevlink("snapshot", name, title, class, head, rev, archivename);
 }
 
 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;
 
         delim = repolink(title, class, "diff", head, path);
         if (new_rev && strcmp(new_rev, ctx.qry.head)) {
                 html(delim);
                 html("id=");
                 html_url_arg(new_rev);
                 delim = "&amp;";
         }
         if (old_rev) {
                 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);
         html("</a>");
 }
 
 void cgit_patch_link(char *name, char *title, char *class, char *head,
                      char *rev)
 {
         reporevlink("patch", name, title, class, head, rev, NULL);
 }
 
@@ -374,25 +396,25 @@ void cgit_stats_link(char *name, char *title, char *class, char *head,
         reporevlink("stats", name, title, class, head, NULL, path);
 }
 
 void cgit_object_link(struct object *obj)
 {
         char *page, *shortrev, *fullrev, *name;
 
         fullrev = sha1_to_hex(obj->sha1);
         shortrev = xstrdup(fullrev);
         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";
         else if (obj->type == OBJ_TAG)
                 page = "tag";
         else
                 page = "blob";
         name = fmt("%s %s...", typename(obj->type), shortrev);
         reporevlink(page, name, NULL, NULL, ctx.qry.head, fullrev, NULL);
 }
 
 void cgit_print_date(time_t secs, char *format, int local_time)
@@ -686,27 +708,27 @@ void cgit_print_pageheader(struct cgit_context *ctx)
 
         html("<table class='tabs'><tr><td>\n");
         if (ctx->repo) {
                 cgit_summary_link("summary", NULL, hc(cmd, "summary"),
                                   ctx->qry.head);
                 cgit_refs_link("refs", NULL, hc(cmd, "refs"), ctx->qry.head,
                                ctx->qry.sha1, NULL);
                 cgit_log_link("log", NULL, hc(cmd, "log"), ctx->qry.head,
                               NULL, NULL, 0, NULL, NULL, ctx->qry.showmsg);
                 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);
                 if (ctx->repo->readme)
                         reporevlink("about", "about", NULL,
                                     hc(cmd, "about"), ctx->qry.head, NULL,
                                     NULL);
                 html("</td><td class='form'>");
                 html("<form class='right' method='get' action='");
                 if (ctx->cfg.virtual_root)
                         html_url_path(cgit_fileurl(ctx->qry.repo, "log",
                                                    ctx->qry.path, NULL));
diff --git a/ui-shared.h b/ui-shared.h
index b12aa89..9ebc1f9 100644
--- a/ui-shared.h
+++ b/ui-shared.h
@@ -14,33 +14,34 @@ extern void cgit_index_link(char *name, char *title, char *class,
                             char *pattern, int ofs);
 extern void cgit_summary_link(char *name, char *title, char *class, char *head);
 extern void cgit_tag_link(char *name, char *title, char *class, char *head,
                           char *rev);
 extern void cgit_tree_link(char *name, char *title, char *class, char *head,
                            char *rev, char *path);
 extern void cgit_plain_link(char *name, char *title, char *class, char *head,
                             char *rev, char *path);
 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,
                            char *rev, char *path);
 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);
 
 extern void cgit_print_error(char *msg);
 extern void cgit_print_date(time_t secs, char *format, int local_time);
 extern void cgit_print_age(time_t t, time_t max_relative, char *format);
 extern void cgit_print_http_headers(struct cgit_context *ctx);
 extern void cgit_print_docstart(struct cgit_context *ctx);
 extern void cgit_print_docend();
 extern void cgit_print_pageheader(struct cgit_context *ctx);
 extern void cgit_print_filemode(unsigned short mode);
diff --git a/ui-ssdiff.c b/ui-ssdiff.c
new file mode 100644
index 0000000..408e620
--- a/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
--- a/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 */