UTF-8文字列を1文字ずつで分解するLuaスクリプト

utf8.lua

-- The MIT License (MIT)
-- 
-- Copyright (c) 2018 oov
-- 
-- Permission is hereby granted, free of charge, to any person obtaining a copy of
-- this software and associated documentation files (the "Software"), to deal in
-- the Software without restriction, including without limitation the rights to
-- use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
-- the Software, and to permit persons to whom the Software is furnished to do so,
-- subject to the following conditions:
-- 
-- The above copyright notice and this permission notice shall be included in all
-- copies or substantial portions of the Software.
-- 
-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
-- FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
-- COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
-- IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
-- CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

-- Reference: https://tools.ietf.org/html/rfc3629#section-4
local function split_by_utf8_char(s)
	local r, cp, p, ln = {}, {}, 1, s:len()
	local c1, c2, c3, c4
	while p <= ln do
		c1 = s:byte(p)
		if 0x00 <= c1 and c1 <= 0x7f then
			table.insert(r, string.char(c1))
			table.insert(cp, c1)
		elseif p + 1 <= ln then
			c2 = s:byte(p + 1)
			if 0xc2 <= c1 and c1 <= 0xdf and 0x80 <= c2 and c2 <= 0xbf then
				table.insert(r, string.char(c1, c2))
				table.insert(cp, (c1 - 0xc0) * 0x40 + (c2 - 0x80))
				p = p + 1
			elseif p + 2 <= ln then
				c3 = s:byte(p + 2)
				if (c1 == 0xe0 and 0xa0 <= c2 and c2 <= 0xbf and 0x80 <= c3 and c3 <= 0xbf)or
					(0xe1 <= c1 and c1 <= 0xec and 0x80 <= c2 and c2 <= 0xbf and 0x80 <= c3 and c3 <= 0xbf)or
					(c1 == 0xed and 0x80 <= c2 and c2 <= 0x9f and 0x80 <= c3 and c3 <= 0xbf)or
					(0xee <= c1 and c1 <= 0xef and 0x80 <= c2 and c2 <= 0xbf and 0x80 <= c3 and c3 <= 0xbf) then
					table.insert(r, string.char(c1, c2, c3))
					table.insert(cp, (c1 - 0xe0) * 0x1000 + (c2 - 0x80) * 0x40 + (c3 - 0x80))
					p = p + 2
				elseif p + 3 <= ln then
					c4 = s:byte(p + 3)
					if (c1 == 0xf0 and 0x90 <= c2 and c2 <= 0xbf and 0x80 <= c3 and c3 <= 0xbf and 0x80 <= c4 and c4 <= 0xbf)or
						(0xf1 <= c1 and c1 <= 0xf3 and 0x80 <= c2 and c2 <= 0xbf and 0x80 <= c3 and c3 <= 0xbf and 0x80 <= c4 and c4 <= 0xbf)or
						(c1 == 0xf4 and 0x80 <= c2 and c2 <= 0x8f and 0x80 <= c3 and c3 <= 0xbf and 0x80 <= c4 and c4 <= 0xbf) then
						table.insert(r, string.char(c1, c2, c3, c4))
						table.insert(cp, (c1 - 0xf0) * 0x40000 + (c2 - 0x80) * 0x1000 + (c3 - 0x80) * 0x40 + (c3 - 0x80))
						p = p + 3
					end
				end
			end
		end
		p = p + 1
	end
	return r, cp
end