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