1 files changed, 18 insertions, 5 deletions
diff --git a/Firestore/core/src/firebase/firestore/model/field_mask.h b/Firestore/core/src/firebase/firestore/model/field_mask.h
index b895ab3..431e05a 100644
--- a/Firestore/core/src/firebase/firestore/model/field_mask.h
+++ b/Firestore/core/src/firebase/firestore/model/field_mask.h
@@ -23,6 +23,7 @@
 #include <vector>
 
 #include "Firestore/core/src/firebase/firestore/model/field_path.h"
+#include "Firestore/core/src/firebase/firestore/util/hashing.h"
 
 namespace firebase {
 namespace firestore {
@@ -55,6 +56,22 @@ class FieldMask {
     return fields_.end();
   }
 
+  /**
+   * Verifies that `fieldPath` is included by at least one field in this field
+   * mask.
+   *
+   * This is an O(n) operation, where `n` is the size of the field mask.
+   */
+  bool covers(const FieldPath& fieldPath) const {
+    for (const FieldPath& fieldMaskPath : fields_) {
+      if (fieldMaskPath.IsPrefixOf(fieldPath)) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
   std::string ToString() const {
     // Ideally, one should use a string builder. Since this is only non-critical
     // code for logging and debugging, the logic is kept simple here.
@@ -70,11 +87,7 @@ class FieldMask {
   }
 
   NSUInteger Hash() const {
-    NSUInteger hashResult = 0;
-    for (const FieldPath& field : fields_) {
-      hashResult = hashResult * 31u + field.Hash();
-    }
-    return hashResult;
+    return util::Hash(fields_);
   }
 #endif