48 lines
2.1 KiB
Swift
48 lines
2.1 KiB
Swift
extension PureXML.Parsing.ByteDecoder {
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/// The GBK index (the GB18030 two-byte range), assembled from the vendored
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/// parts. Decodes GB2312 too, which GBK is a superset of.
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static let gbk: [UInt16] = gbkPart1 + gbkPart2 + gbkPart3 + gbkPart4 + gbkPart5 + gbkPart6
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/// The GBK decoder (the WHATWG `GBK` algorithm, the two-byte subset of
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/// GB18030): ASCII directly, `0x80` as the euro sign, and a lead in
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/// `0x81`-`0xFE` followed by a trail resolved through the index.
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enum GBK {
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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 byte == 0x80 {
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scalars.append("\u{20AC}") // euro
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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 GBK 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 (0x40 ... 0x7E).contains(trail) || (0x80 ... 0xFE).contains(trail) else { return nil }
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let offset = trail < 0x7F ? 0x40 : 0x41
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let pointer = (Int(lead) - 0x81) * 190 + Int(trail) - offset
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guard pointer >= 0, pointer < gbk.count, gbk[pointer] != 0xFFFF else { return nil }
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return Unicode.Scalar(UInt32(gbk[pointer]))
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}
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}
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}
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