1 files changed, 46 insertions, 0 deletions
diff --git a/zap/src/mem/strlen.S b/zap/src/mem/strlen.S
new file mode 100644
index 0000000..4cb435f
--- /dev/null
+++ b/zap/src/mem/strlen.S
@@ -0,0 +1,46 @@
+/*
+	Copyright 2022 Gabriel Jensen.
+	This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
+	If a copy of the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.
+*/
+
+#include <zap/priv.h>
+
+.globl zap_strlen
+
+zap_strlen:
+
+	/*
+		char const * str
+	*/
+
+#if defined(__amd64__)
+
+	# rax: Address of the current character.
+	# rdx: Current character.
+
+	movq %rdi,%rax
+
+	# Iterate over the string:
+.loop:
+
+	# Move the character into a register:
+	movb (%rax),%dl
+
+	# Check if we have reached the null-terminator:
+	testb %dl,%dl
+	jz .done # If so, we are done.
+
+	# Continue to the next character:
+	incq %rax
+	jmp .loop
+
+	# Done:
+.done:
+
+	# Get the length:
+	subq %rdi,%rax
+
+	ret
+
+#endif