1 files changed, 43 insertions, 0 deletions
diff --git a/zap/source/amd64/mem/fndchr.S b/zap/source/amd64/mem/fndchr.S
new file mode 100644
index 0000000..1078a10
--- /dev/null
+++ b/zap/source/amd64/mem/fndchr.S
@@ -0,0 +1,43 @@
+# 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/.
+
+.globl zap_fndchr
+
+zap_fndchr:
+ # rdi: Address of the first character.
+ # rsi: Character to be found.
+ # rax: Address of the current character.
+ # rdx: Current character.
+
+ movq %rdi,%rax
+
+ # Iterate over the string:
+.loop:
+
+ # Copy the character into a register:
+ movb (%rax),%dl
+
+ # Check if we have found the character:
+ cmpb %dl,%sil
+ je .fnd
+
+ # Check if we have found the null-terminator:
+ testb %dl,%dl
+ jz .nfnd
+
+ # Continue to the next character:
+ incq %rax
+ jmp .loop
+
+ # Found:
+.fnd:
+
+ subq %rdi,%rax
+ ret
+
+ # Not found:
+.nfnd:
+
+ movq $0xFFFFFFFFFFFFFFFF,%rax
+ ret