51 lines
1.3 KiB
Lua
51 lines
1.3 KiB
Lua
local lpeg = require("lpeg")
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local string = string
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module("utf8_processor")
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local function encode_utf(codepoint)
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if codepoint > 0x10FFFF then
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error("Codepoint > 10FFFF cannot be encoded")
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elseif codepoint > 0xFFFF then
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-- Surrogate pair needed
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codepoint = codepoint - 0x10000
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local first, second = codepoint / 0x0400 + 0xD800, codepoint % 0x0400 + 0xDC00
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return ("\\u%.4X\\u%.4X"):format(first, second)
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else
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return ("\\u%.4X"):format(codepoint)
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end
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end
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-- decode a two-byte UTF-8 sequence
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local function f2 (s)
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local c1, c2 = string.byte(s, 1, 2)
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return encode_utf(c1 * 64 + c2 - 12416)
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end
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-- decode a three-byte UTF-8 sequence
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local function f3 (s)
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local c1, c2, c3 = string.byte(s, 1, 3)
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return encode_utf((c1 * 64 + c2) * 64 + c3 - 925824)
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end
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-- decode a four-byte UTF-8 sequence
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local function f4 (s)
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local c1, c2, c3, c4 = string.byte(s, 1, 4)
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return encode_utf(((c1 * 64 + c2) * 64 + c3) * 64 + c4 - 63447168)
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end
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local cont = lpeg.R("\128\191") -- continuation byte
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local utf8 = lpeg.R("\0\127") -- Do nothing here
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+ lpeg.R("\194\223") * cont / f2
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+ lpeg.R("\224\239") * cont * cont / f3
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+ lpeg.R("\240\244") * cont * cont * cont / f4
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local utf8_decode_pattern = lpeg.Cs(utf8^0) * -1
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function process(s)
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return utf8_decode_pattern:match(s)
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end
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