# 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_strlen zap_strlen: # 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