1 files changed, 25 insertions, 0 deletions
diff --git a/lib/libc/string/swab.c b/lib/libc/string/swab.c
new file mode 100644
index 000000000000..ed4436a49810
--- /dev/null
+++ b/lib/libc/string/swab.c
@@ -0,0 +1,25 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ * Copyright (c) 2024 rilysh <nightquick@proton.me>
+ */
+
+#include <unistd.h>
+#include <sys/endian.h>
+
+void
+swab(const void * __restrict from, void * __restrict to, ssize_t len)
+{
+	const uint16_t *f __aligned(1) = from;
+	uint16_t *t __aligned(1) = to;
+
+	/*
+	 * POSIX says overlapping copy behavior is undefined, however many
+	 * applications assume the old FreeBSD and current GNU libc behavior
+	 * that will swap the bytes correctly when from == to. Reading both bytes
+	 * and swapping them before writing them back accomplishes this.
+	 */
+	while (len > 1) {
+		*t++ = bswap16(*f++);
+		len -= 2;
+	}
+}