44 lines
1.9 KiB
Swift
44 lines
1.9 KiB
Swift
extension PureXML.Parsing.ByteDecoder {
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/// The EUC-KR (CP949/UHC) index, assembled from the vendored parts.
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static let eucKR: [UInt16] = eucKRPart1 + eucKRPart2 + eucKRPart3 + eucKRPart4 + eucKRPart5 + eucKRPart6
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/// The EUC-KR decoder (the WHATWG `EUC-KR` algorithm): ASCII directly, any
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/// other byte in `0x81`-`0xFE` as a lead followed by a trail resolved through
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/// the CP949 index.
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enum EUCKR {
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static func decode(_ bytes: ArraySlice<UInt8>) -> String {
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var scalars = String.UnicodeScalarView()
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var lead: UInt8 = 0
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for byte in bytes {
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if lead != 0 {
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let saved = lead
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lead = 0
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if let scalar = twoByteScalar(lead: saved, trail: byte) {
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scalars.append(scalar)
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} else {
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scalars.append("\u{FFFD}")
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if byte <= 0x7F { scalars.append(Unicode.Scalar(byte)) }
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}
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} else if byte <= 0x7F {
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scalars.append(Unicode.Scalar(byte))
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} else if (0x81 ... 0xFE).contains(byte) {
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lead = byte
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} else {
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scalars.append("\u{FFFD}")
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}
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}
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if lead != 0 { scalars.append("\u{FFFD}") }
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return String(scalars)
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}
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/// The scalar for a `(lead, trail)` pair through the CP949 index, or nil for
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/// an invalid or unmapped pair.
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static func twoByteScalar(lead: UInt8, trail: UInt8) -> Unicode.Scalar? {
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guard (0x41 ... 0xFE).contains(trail) else { return nil }
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let pointer = (Int(lead) - 0x81) * 190 + Int(trail) - 0x41
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guard pointer >= 0, pointer < eucKR.count, eucKR[pointer] != 0xFFFF else { return nil }
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return Unicode.Scalar(UInt32(eucKR[pointer]))
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}
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}
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}
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