path: root/zap/source/amd64/mem/utf8enclen.S

# 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_utf8enclen

zap_utf8enclen:
	# rdi: Address of the current character.
	# rax: Length of the string.
	# rsi: Current character.

	movq $0x0,%rax

	# Iterate over the input:
.loop:

	movl (%rdi),%esi

	# Test if we have reached the null-terminator:
	testl %esi,%esi
	jz .done

	cmpl $0xFFFF,%esi
	jg .oct4

	cmpl $0x7FF,%esi
	jg .oct3

	cmpl $0x7F,%esi
	jg .oct2

	# One octet:
.oct1:

	incq %rax

	jmp .cnt

	# Two octets:
.oct2:

	addq $0x2,%rax

	jmp .cnt

	# Three octets:
.oct3:

	addq $0x3,%rax

	jmp .cnt

	# Four octets:
.oct4:

	addq $0x4,%rax

	# Continue to the next codepoint:
.cnt:

	addq $0x4,%rdi
	jmp .loop

	# Done:
.done:

	ret