diff -r b1eac0878ce7 -r 18892c0a9adc ucx/map.c
--- a/ucx/map.c	Sat Dec 05 10:34:10 2020 +0100
+++ b/ucx/map.c	Sat Dec 05 11:54:58 2020 +0100
@@ -103,7 +103,7 @@
     map->count = 0;
 }
 
-int ucx_map_copy(UcxMap *from, UcxMap *to, copy_func fnc, void *data) {
+int ucx_map_copy(UcxMap const *from, UcxMap *to, copy_func fnc, void *data) {
     UcxMapIterator i = ucx_map_iterator(from);
     void *value;
     UCX_MAP_FOREACH(key, value, i) {
@@ -114,9 +114,14 @@
     return 0;
 }
 
-UcxMap *ucx_map_clone(UcxMap *map, copy_func fnc, void *data) {
+UcxMap *ucx_map_clone(UcxMap const *map, copy_func fnc, void *data) {
+    return ucx_map_clone_a(ucx_default_allocator(), map, fnc, data);
+}
+
+UcxMap *ucx_map_clone_a(UcxAllocator *allocator,
+        UcxMap const *map, copy_func fnc, void *data) {
     size_t bs = (map->count * 5) >> 1;
-    UcxMap *newmap = ucx_map_new(bs > map->size ? bs : map->size);
+    UcxMap *newmap = ucx_map_new_a(allocator, bs > map->size ? bs : map->size);
     if (!newmap) {
         return NULL;
     }
@@ -235,8 +240,8 @@
     return NULL;
 }
 
-void *ucx_map_get(UcxMap *map, UcxKey key) {
-    return ucx_map_get_and_remove(map, key, 0);
+void *ucx_map_get(UcxMap const *map, UcxKey key) {
+    return ucx_map_get_and_remove((UcxMap *)map, key, 0);
 }
 
 void *ucx_map_remove(UcxMap *map, UcxKey key) {
@@ -294,7 +299,7 @@
     return h;
 }
 
-UcxMapIterator ucx_map_iterator(UcxMap *map) {
+UcxMapIterator ucx_map_iterator(UcxMap const *map) {
     UcxMapIterator i;
     i.map = map;
     i.cur = NULL;
@@ -335,3 +340,63 @@
     return 0;
 }
 
+UcxMap* ucx_map_union(const UcxMap *first, const UcxMap *second,
+                      copy_func cpfnc, void* cpdata) {
+    return ucx_map_union_a(ucx_default_allocator(),
+            first, second, cpfnc, cpdata);
+}
+
+UcxMap* ucx_map_union_a(UcxAllocator *allocator,
+                        const UcxMap *first, const UcxMap *second,
+                        copy_func cpfnc, void* cpdata) {
+    UcxMap* result = ucx_map_clone_a(allocator, first, cpfnc, cpdata);
+    ucx_map_copy(second, result, cpfnc, cpdata);
+    return result;
+}
+
+UcxMap* ucx_map_intersection(const UcxMap *first, const UcxMap *second,
+                             copy_func cpfnc, void* cpdata) {
+    return ucx_map_intersection_a(ucx_default_allocator(),
+            first, second, cpfnc, cpdata);
+}
+
+UcxMap* ucx_map_intersection_a(UcxAllocator *allocator,
+                               const UcxMap *first, const UcxMap *second,
+                               copy_func cpfnc, void* cpdata) {
+    UcxMap *result = ucx_map_new_a(allocator, first->size < second->size ?
+            first->size : second->size);
+
+    UcxMapIterator iter = ucx_map_iterator(first);
+    void* value;
+    UCX_MAP_FOREACH(key, value, iter) {
+        if (ucx_map_get(second, key)) {
+            ucx_map_put(result, key, cpfnc ? cpfnc(value, cpdata) : value);
+        }
+    }
+
+    return result;
+}
+
+UcxMap* ucx_map_difference(const UcxMap *first, const UcxMap *second,
+                           copy_func cpfnc, void* cpdata) {
+    return ucx_map_difference_a(ucx_default_allocator(),
+            first, second, cpfnc, cpdata);
+}
+
+UcxMap* ucx_map_difference_a(UcxAllocator *allocator,
+                             const UcxMap *first, const UcxMap *second,
+                             copy_func cpfnc, void* cpdata) {
+
+    UcxMap *result = ucx_map_new_a(allocator, first->size - second->count);
+
+    UcxMapIterator iter = ucx_map_iterator(first);
+    void* value;
+    UCX_MAP_FOREACH(key, value, iter) {
+        if (!ucx_map_get(second, key)) {
+            ucx_map_put(result, key, cpfnc ? cpfnc(value, cpdata) : value);
+        }
+    }
+
+    ucx_map_rehash(result);
+    return result;
+}
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