diff options
Diffstat (limited to 'rgo/src/strlen.S')
-rw-r--r-- | rgo/src/strlen.S | 35 |
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 |