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local lpeg = require("lpeg")
local string = string
local floor = require("math").floor
local _ENV = nil
local function encode_utf(codepoint)
if codepoint > 0x10FFFF then
error("Codepoint > 10FFFF cannot be encoded")
elseif codepoint > 0xFFFF then
-- Surrogate pair needed
codepoint = codepoint - 0x10000
local first, second = floor(codepoint / 0x0400) + 0xD800, codepoint % 0x0400 + 0xDC00
return ("\\u%.4X\\u%.4X"):format(first, second)
else
return ("\\u%.4X"):format(codepoint)
end
end
-- decode a two-byte UTF-8 sequence
local function f2 (s)
local c1, c2 = string.byte(s, 1, 2)
return encode_utf(c1 * 64 + c2 - 12416)
end
-- decode a three-byte UTF-8 sequence
local function f3 (s)
local c1, c2, c3 = string.byte(s, 1, 3)
return encode_utf((c1 * 64 + c2) * 64 + c3 - 925824)
end
-- decode a four-byte UTF-8 sequence
local function f4 (s)
local c1, c2, c3, c4 = string.byte(s, 1, 4)
return encode_utf(((c1 * 64 + c2) * 64 + c3) * 64 + c4 - 63447168)
end
local cont = lpeg.R("\128\191") -- continuation byte
local utf8 = lpeg.R("\0\127") -- Do nothing here
+ lpeg.R("\194\223") * cont / f2
+ lpeg.R("\224\239") * cont * cont / f3
+ lpeg.R("\240\244") * cont * cont * cont / f4
local utf8_decode_pattern = lpeg.Cs(utf8^0) * -1
local function process(s)
return utf8_decode_pattern:match(s)
end
return {
process = process
}
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