Add comment on how mbedtls_gcm_context::buf data depends on
values of add_len and len.
@@ -332,7 +332,16 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
return( 0 );
}
-
+/**
+ * mbedtls_gcm_context::buf contains different data type, depending
+ * on the values of mbedtls_gcm_context::::add_len and
+ * mbedtls_gcm_context::len:
+ * * When add_len % 16 == 0 and len == 0: initial state.
+ * * When add_len % 16 != 0 and len == 0: the first `add_len % 16` bytes
+ * of buf have a partial AD block xored in and not yet multiplied in.
+ * * When len != 0: the first `add_len % 16` bytes of buf have partial
+ * ciphertext xored in and not yet multiplied in.
+ */
int mbedtls_gcm_update_ad( mbedtls_gcm_context *ctx,
const unsigned char *add, size_t add_len )
{
