xdiff/xpatience: factor out fall-back-diff function

This is in preparation for the histogram diff algorithm, which will also
re-use much of the code to call the default Meyers diff algorithm.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 35 insertions, 25 deletions

diff --git a/xdiff/xpatience.c b/xdiff/xpatience.c
index e42c16a80..fdd7d0263 100644
--- a/xdiff/xpatience.c
+++ b/xdiff/xpatience.c
@@ -287,34 +287,11 @@ static int walk_common_sequence(struct hashmap *map, struct entry *first,
 static int fall_back_to_classic_diff(struct hashmap *map,
 		int line1, int count1, int line2, int count2)
 {
-	/*
-	 * This probably does not work outside Git, since
-	 * we have a very simple mmfile structure.
-	 *
-	 * Note: ideally, we would reuse the prepared environment, but
-	 * the libxdiff interface does not (yet) allow for diffing only
-	 * ranges of lines instead of the whole files.
-	 */
-	mmfile_t subfile1, subfile2;
 	xpparam_t xpp;
-	xdfenv_t env;
-
-	subfile1.ptr = (char *)map->env->xdf1.recs[line1 - 1]->ptr;
-	subfile1.size = map->env->xdf1.recs[line1 + count1 - 2]->ptr +
-		map->env->xdf1.recs[line1 + count1 - 2]->size - subfile1.ptr;
-	subfile2.ptr = (char *)map->env->xdf2.recs[line2 - 1]->ptr;
-	subfile2.size = map->env->xdf2.recs[line2 + count2 - 2]->ptr +
-		map->env->xdf2.recs[line2 + count2 - 2]->size - subfile2.ptr;
 	xpp.flags = map->xpp->flags & ~XDF_PATIENCE_DIFF;
-	if (xdl_do_diff(&subfile1, &subfile2, &xpp, &env) < 0)
-		return -1;
 
-	memcpy(map->env->xdf1.rchg + line1 - 1, env.xdf1.rchg, count1);
-	memcpy(map->env->xdf2.rchg + line2 - 1, env.xdf2.rchg, count2);
-
-	xdl_free_env(&env);
-
-	return 0;
+	return xdl_fall_back_diff(map->env, &xpp,
+				  line1, count1, line2, count2);
 }
 
 /*
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index ab6503460..ded7c327d 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -402,3 +402,34 @@ int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
 
 	return 0;
 }
+
+int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
+		int line1, int count1, int line2, int count2)
+{
+	/*
+	 * This probably does not work outside Git, since
+	 * we have a very simple mmfile structure.
+	 *
+	 * Note: ideally, we would reuse the prepared environment, but
+	 * the libxdiff interface does not (yet) allow for diffing only
+	 * ranges of lines instead of the whole files.
+	 */
+	mmfile_t subfile1, subfile2;
+	xdfenv_t env;
+
+	subfile1.ptr = (char *)diff_env->xdf1.recs[line1 - 1]->ptr;
+	subfile1.size = diff_env->xdf1.recs[line1 + count1 - 2]->ptr +
+		diff_env->xdf1.recs[line1 + count1 - 2]->size - subfile1.ptr;
+	subfile2.ptr = (char *)diff_env->xdf2.recs[line2 - 1]->ptr;
+	subfile2.size = diff_env->xdf2.recs[line2 + count2 - 2]->ptr +
+		diff_env->xdf2.recs[line2 + count2 - 2]->size - subfile2.ptr;
+	if (xdl_do_diff(&subfile1, &subfile2, xpp, &env) < 0)
+		return -1;
+
+	memcpy(diff_env->xdf1.rchg + line1 - 1, env.xdf1.rchg, count1);
+	memcpy(diff_env->xdf2.rchg + line2 - 1, env.xdf2.rchg, count2);
+
+	xdl_free_env(&env);
+
+	return 0;
+}
diff --git a/xdiff/xutils.h b/xdiff/xutils.h
index d5de8292e..674a657b0 100644
--- a/xdiff/xutils.h
+++ b/xdiff/xutils.h
@@ -41,6 +41,8 @@ int xdl_num_out(char *out, long val);
 long xdl_atol(char const *str, char const **next);
 int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
 		      const char *func, long funclen, xdemitcb_t *ecb);
+int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
+		       int line1, int count1, int line2, int count2);