diff options
Diffstat (limited to 'rgo/src/fndchr.S')
-rw-r--r-- | rgo/src/fndchr.S | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/rgo/src/fndchr.S b/rgo/src/fndchr.S new file mode 100644 index 0000000..97c3768 --- /dev/null +++ b/rgo/src/fndchr.S @@ -0,0 +1,40 @@ +/* + 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_fndchr + +rgo_fndchr: +#if defined(__x86_64__) + /* + rdi: char const * str + sil: char chr + */ + /* rax: Address of the current character. */ + movq %rdi,%rax + /* dl: Current character. */ +.loop: + movb (%rax),%dl + cmpb %dl,%sil + je .done /* Exit loop if we have found the character. */ + testb %dl,%dl + je .err /* We encounted the null-terminator but not the specified character. */ + incq %rax + jmp .loop +.done: + subq %rdi,%rax + ret +.err: + movq $0xFFFFFFFFFFFFFFFF,%rax + ret +#endif |