Move mbedtls_cf_memcmp to a new public header
Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/include/mbedtls/constant_time.h b/include/mbedtls/constant_time.h
new file mode 100644
index 0000000..69df954
--- /dev/null
+++ b/include/mbedtls/constant_time.h
@@ -0,0 +1,47 @@
+/**
+ * Constant-time functions
+ *
+ * Copyright The Mbed TLS Contributors
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef MBEDTLS_CONSTANT_TIME_H
+#define MBEDTLS_CONSTANT_TIME_H
+
+#include "common.h"
+
+#include <stddef.h>
+
+
+/** Constant-time buffer comparison without branches.
+ *
+ * This is equivalent to the standard memncmp function, but is likely to be
+ * compiled to code using bitwise operation rather than a branch.
+ *
+ * This function can be used to write constant-time code by replacing branches
+ * with bit operations using masks.
+ *
+ * \param a Pointer to the first buffer.
+ * \param b Pointer to the second buffer.
+ * \param n The number of bytes to compare in the buffer.
+ *
+ * \return Zero if the content of the two buffer is the same,
+ * otherwise non-zero.
+ */
+int mbedtls_cf_memcmp( const void *a,
+ const void *b,
+ size_t n );
+
+#endif /* MBEDTLS_CONSTANT_TIME_H */