Document rename_replace_existing macro
diff --git a/library/psa_its_file.c b/library/psa_its_file.c
index bc0f84c..8cdf783 100644
--- a/library/psa_its_file.c
+++ b/library/psa_its_file.c
@@ -62,9 +62,12 @@
#define PSA_ITS_MAGIC_STRING "PSA\0ITS\0"
#define PSA_ITS_MAGIC_LENGTH 8
+/* As rename fails on Windows if the new filepath already exists,
+ * use MoveFileExA with the MOVEFILE_REPLACE_EXISTING flag instead.
+ * Returns 0 on success, nonzero on failure. */
#if defined(_WIN32)
#define rename_replace_existing( oldpath, newpath ) \
- (!MoveFileExA( oldpath, newpath, MOVEFILE_REPLACE_EXISTING ))
+ ( ! MoveFileExA( oldpath, newpath, MOVEFILE_REPLACE_EXISTING ) )
#else
#define rename_replace_existing( oldpath, newpath ) rename( oldpath, newpath )
#endif