xdiff-interface: export comparing and hashing strings

This will turn out to be useful in a later patch.

xdl_recmatch is exported in xdiff/xutils.h, to be used by various
xdiff/*.c files, but not outside of xdiff/. This one makes it available
to the outside, too.

While at it, add documentation.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

xdiff-interface.c

@@ -5,6 +5,7 @@
 #include "xdiff/xdiffi.h"
 #include "xdiff/xemit.h"
 #include "xdiff/xmacros.h"
+#include "xdiff/xutils.h"
 
 struct xdiff_emit_state {
 	xdiff_emit_consume_fn consume;
@@ -296,6 +297,17 @@ void xdiff_clear_find_func(xdemitconf_t *xecfg)
 	}
 }
 
+unsigned long xdiff_hash_string(const char *s, size_t len, long flags)
+{
+	return xdl_hash_record(&s, s + len, flags);
+}
+
+int xdiff_compare_lines(const char *l1, long s1,
+			const char *l2, long s2, long flags)
+{
+	return xdl_recmatch(l1, s1, l2, s2, flags);
+}
+
 int git_xmerge_style = -1;
 
 int git_xmerge_config(const char *var, const char *value, void *cb)