From f1d94290bd5e6200ec21fcc4f0df3f76e9f7f3bc Mon Sep 17 00:00:00 2001
From: Sven Verdoolaege <skimo@kotnet.org>
Date: Mon, 21 Mar 2016 16:43:09 +0100
Subject: [PATCH] add isl_map_is_identity

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>
---
 doc/user.pod      |  9 +++++++++
 include/isl/map.h |  1 +
 isl_map.c         | 27 +++++++++++++++++++++++++++
 3 files changed, 37 insertions(+)

diff --git a/doc/user.pod b/doc/user.pod
index c5e23797..e747f8d6 100644
--- a/doc/user.pod
+++ b/doc/user.pod
@@ -3772,6 +3772,15 @@ is already known to be empty.
 	isl_bool isl_union_map_is_bijective(
 		__isl_keep isl_union_map *umap);
 
+=item * Identity
+
+The following function tests whether the given relation
+only maps elements to themselves.
+
+	#include <isl/map.h>
+	isl_bool isl_map_is_identity(
+		__isl_keep isl_map *map);
+
 =item * Position
 
 	__isl_give isl_val *
diff --git a/include/isl/map.h b/include/isl/map.h
index fdbac8cc..c46d2572 100644
--- a/include/isl/map.h
+++ b/include/isl/map.h
@@ -541,6 +541,7 @@ __isl_export
 isl_bool isl_map_is_injective(__isl_keep isl_map *map);
 __isl_export
 isl_bool isl_map_is_bijective(__isl_keep isl_map *map);
+isl_bool isl_map_is_identity(__isl_keep isl_map *map);
 int isl_map_is_translation(__isl_keep isl_map *map);
 int isl_map_has_equal_space(__isl_keep isl_map *map1, __isl_keep isl_map *map2);
 
diff --git a/isl_map.c b/isl_map.c
index 50c0521b..a34368b0 100644
--- a/isl_map.c
+++ b/isl_map.c
@@ -3,6 +3,7 @@
  * Copyright 2010      INRIA Saclay
  * Copyright 2012-2014 Ecole Normale Superieure
  * Copyright 2014      INRIA Rocquencourt
+ * Copyright 2016      Sven Verdoolaege
  *
  * Use of this software is governed by the MIT license
  *
@@ -10898,6 +10899,32 @@ isl_bool isl_set_is_singleton(__isl_keep isl_set *set)
 	return isl_map_is_single_valued((isl_map *)set);
 }
 
+/* Does "map" only map elements to themselves?
+ *
+ * If the domain and range spaces are different, then "map"
+ * is considered not to be an identity relation, even if it is empty.
+ * Otherwise, construct the maximal identity relation and
+ * check whether "map" is a subset of this relation.
+ */
+isl_bool isl_map_is_identity(__isl_keep isl_map *map)
+{
+	isl_space *space;
+	isl_map *id;
+	isl_bool equal, is_identity;
+
+	space = isl_map_get_space(map);
+	equal = isl_space_tuple_is_equal(space, isl_dim_in, space, isl_dim_out);
+	isl_space_free(space);
+	if (equal < 0 || !equal)
+		return equal;
+
+	id = isl_map_identity(isl_map_get_space(map));
+	is_identity = isl_map_is_subset(map, id);
+	isl_map_free(id);
+
+	return is_identity;
+}
+
 int isl_map_is_translation(__isl_keep isl_map *map)
 {
 	int ok;
-- 
2.11.4.GIT