local char, byte, pairs, floor = string.char, string.byte, pairs, math.floor
local table_insert, table_concat = table.insert, table.concat
local unpack = table.unpack or unpack

local function unicode_to_utf8(code)
	-- converts numeric UTF code (U+code) to UTF-8 string
	local t, h = {}, 128
	while code >= h do
		t[#t+1] = 128 + code%64
		code = floor(code/64)
		h = h > 32 and 32 or h/2
	end
	t[#t+1] = 256 - 2*h + code
	return char(unpack(t)):reverse()
end

local function utf8_to_unicode(utf8str, pos)
	-- pos = starting byte position inside input string (default 1)
	pos = pos or 1
	local code, size = utf8str:byte(pos), 1
	if code >= 0xC0 and code < 0xFE then
		local mask = 64
		code = code - 128
		repeat
			local next_byte = utf8str:byte(pos + size) or 0
			if next_byte >= 0x80 and next_byte < 0xC0 then
				code, size = (code - mask - 2) * 64 + next_byte, size + 1
			else
				code, size = utf8str:byte(pos), 1
			end
			mask = mask * 32
		until code < mask
	end
	-- returns code, number of bytes in this utf8 char
	return code, size
end

local map_1252_to_unicode = {
	[0x80] = 0x20AC,
	[0x81] = 0x81,
	[0x82] = 0x201A,
	[0x83] = 0x0192,
	[0x84] = 0x201E,
	[0x85] = 0x2026,
	[0x86] = 0x2020,
	[0x87] = 0x2021,
	[0x88] = 0x02C6,
	[0x89] = 0x2030,
	[0x8A] = 0x0160,
	[0x8B] = 0x2039,
	[0x8C] = 0x0152,
	[0x8D] = 0x8D,
	[0x8E] = 0x017D,
	[0x8F] = 0x8F,
	[0x90] = 0x90,
	[0x91] = 0x2018,
	[0x92] = 0x2019,
	[0x93] = 0x201C,
	[0x94] = 0x201D,
	[0x95] = 0x2022,
	[0x96] = 0x2013,
	[0x97] = 0x2014,
	[0x98] = 0x02DC,
	[0x99] = 0x2122,
	[0x9A] = 0x0161,
	[0x9B] = 0x203A,
	[0x9C] = 0x0153,
	[0x9D] = 0x9D,
	[0x9E] = 0x017E,
	[0x9F] = 0x0178,
	[0xA0] = 0x00A0,
	[0xA1] = 0x00A1,
	[0xA2] = 0x00A2,
	[0xA3] = 0x00A3,
	[0xA4] = 0x00A4,
	[0xA5] = 0x00A5,
	[0xA6] = 0x00A6,
	[0xA7] = 0x00A7,
	[0xA8] = 0x00A8,
	[0xA9] = 0x00A9,
	[0xAA] = 0x00AA,
	[0xAB] = 0x00AB,
	[0xAC] = 0x00AC,
	[0xAD] = 0x00AD,
	[0xAE] = 0x00AE,
	[0xAF] = 0x00AF,
	[0xB0] = 0x00B0,
	[0xB1] = 0x00B1,
	[0xB2] = 0x00B2,
	[0xB3] = 0x00B3,
	[0xB4] = 0x00B4,
	[0xB5] = 0x00B5,
	[0xB6] = 0x00B6,
	[0xB7] = 0x00B7,
	[0xB8] = 0x00B8,
	[0xB9] = 0x00B9,
	[0xBA] = 0x00BA,
	[0xBB] = 0x00BB,
	[0xBC] = 0x00BC,
	[0xBD] = 0x00BD,
	[0xBE] = 0x00BE,
	[0xBF] = 0x00BF,
	[0xC0] = 0x00C0,
	[0xC1] = 0x00C1,
	[0xC2] = 0x00C2,
	[0xC3] = 0x00C3,
	[0xC4] = 0x00C4,
	[0xC5] = 0x00C5,
	[0xC6] = 0x00C6,
	[0xC7] = 0x00C7,
	[0xC8] = 0x00C8,
	[0xC9] = 0x00C9,
	[0xCA] = 0x00CA,
	[0xCB] = 0x00CB,
	[0xCC] = 0x00CC,
	[0xCD] = 0x00CD,
	[0xCE] = 0x00CE,
	[0xCF] = 0x00CF,
	[0xD0] = 0x00D0,
	[0xD1] = 0x00D1,
	[0xD2] = 0x00D2,
	[0xD3] = 0x00D3,
	[0xD4] = 0x00D4,
	[0xD5] = 0x00D5,
	[0xD6] = 0x00D6,
	[0xD7] = 0x00D7,
	[0xD8] = 0x00D8,
	[0xD9] = 0x00D9,
	[0xDA] = 0x00DA,
	[0xDB] = 0x00DB,
	[0xDC] = 0x00DC,
	[0xDD] = 0x00DD,
	[0xDE] = 0x00DE,
	[0xDF] = 0x00DF,
	[0xE0] = 0x00E0,
	[0xE1] = 0x00E1,
	[0xE2] = 0x00E2,
	[0xE3] = 0x00E3,
	[0xE4] = 0x00E4,
	[0xE5] = 0x00E5,
	[0xE6] = 0x00E6,
	[0xE7] = 0x00E7,
	[0xE8] = 0x00E8,
	[0xE9] = 0x00E9,
	[0xEA] = 0x00EA,
	[0xEB] = 0x00EB,
	[0xEC] = 0x00EC,
	[0xED] = 0x00ED,
	[0xEE] = 0x00EE,
	[0xEF] = 0x00EF,
	[0xF0] = 0x00F0,
	[0xF1] = 0x00F1,
	[0xF2] = 0x00F2,
	[0xF3] = 0x00F3,
	[0xF4] = 0x00F4,
	[0xF5] = 0x00F5,
	[0xF6] = 0x00F6,
	[0xF7] = 0x00F7,
	[0xF8] = 0x00F8,
	[0xF9] = 0x00F9,
	[0xFA] = 0x00FA,
	[0xFB] = 0x00FB,
	[0xFC] = 0x00FC,
	[0xFD] = 0x00FD,
	[0xFE] = 0x00FE,
	[0xFF] = 0x00FF,
}
local map_unicode_to_1252 = {}
for code1252, code in pairs(map_1252_to_unicode) do
	map_unicode_to_1252[code] = code1252
end

function string.fromutf8(utf8str)
	local pos, result_1252 = 1, {}
	while pos <= #utf8str do
		local code, size = utf8_to_unicode(utf8str, pos)
		pos = pos + size
		code = code < 128 and code or map_unicode_to_1252[code] or ('?'):byte()
		table_insert(result_1252, char(code))
	end
	return table_concat(result_1252)
end

function string.toutf8(str1252)
	local result_utf8 = {}
	for pos = 1, #str1252 do
		local code = str1252:byte(pos)
		table_insert(result_utf8, unicode_to_utf8(map_1252_to_unicode[code] or code))
	end
	return table_concat(result_utf8)
end