1 files changed, 67 insertions, 0 deletions
diff --git a/zap/source/amd64/mem/utf8enclen.S b/zap/source/amd64/mem/utf8enclen.S
new file mode 100644
index 0000000..2e3b09f
--- /dev/null
+++ b/zap/source/amd64/mem/utf8enclen.S
@@ -0,0 +1,67 @@
+# 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