1 files changed, 35 insertions, 0 deletions
diff --git a/rgo/src/strlen.S b/rgo/src/strlen.S
new file mode 100644
index 0000000..ff6ed70
--- /dev/null
+++ b/rgo/src/strlen.S
@@ -0,0 +1,35 @@
+/*
+ Copyright 2022 Gabriel Jensen
+
+ This file is part of rgo.
+
+ rgo is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
+
+ rgo is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License along with rgo. If not, see <https://www.gnu.org/licenses/>. 
+*/
+
+#include <rgo.h>
+
+.global rgo_strlen
+
+rgo_strlen:
+#if defined(__x86_64__)
+ /*
+ rdi: char const * str
+ */
+ /* rsi: Address of the current character. */
+ movq %rdi,%rsi
+ /* dl: Current character. */
+.loop:
+ movb (%rsi),%dl
+ testb %dl,%dl
+ jz .done /* Exit loop if we have reached the null-terminator. */
+ incq %rsi /* Continue to the next character. */
+ jmp .loop
+.done:
+ movq %rsi,%rax
+ subq %rdi,%rax
+ ret
+#endif