46 lines
1.7 KiB
C#
46 lines
1.7 KiB
C#
using System.Text;
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namespace Age.Engine.Sys4;
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public static class Sys4StringCodec
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{
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private static readonly Encoding Cp932;
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static Sys4StringCodec()
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{
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Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
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Cp932 = Encoding.GetEncoding(932);
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}
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public static (string? Text, int NDwords) Decode(IReadOnlyList<uint> dwords, int start, int limit = 4096)
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{
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int n = dwords.Count, end = Math.Min(start + limit, n);
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var raw = new List<byte>();
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bool sawNul = false;
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for (int j = start; j < end; j++)
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{
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uint x = dwords[j] ^ 0xFFFFFFFFu;
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raw.Add((byte)(x & 0xFF)); raw.Add((byte)((x >> 8) & 0xFF));
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raw.Add((byte)((x >> 16) & 0xFF)); raw.Add((byte)((x >> 24) & 0xFF));
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if (raw[^1] == 0 || raw[^2] == 0 || raw[^3] == 0 || raw[^4] == 0) { sawNul = true; break; }
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}
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if (!sawNul) return (null, 0);
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int nul = raw.IndexOf(0);
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byte[] s = raw.GetRange(0, nul < 0 ? raw.Count : nul).ToArray();
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if (s.Length < 1) return ("", 1);
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int i = 0, chars = 0;
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while (i < s.Length)
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{
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byte b = s[i];
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if (b >= 0x20 && b <= 0x7E) { i++; chars++; }
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else if ((b >= 0x81 && b <= 0x9F) || (b >= 0xE0 && b <= 0xEA))
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{
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if (i + 1 < s.Length && s[i + 1] >= 0x40 && s[i + 1] <= 0xFC && s[i + 1] != 0x7F) { i += 2; chars++; }
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else return (null, 0);
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}
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else return (null, 0);
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}
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if (chars < 1) return (null, 0);
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string text;
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try { text = Cp932.GetString(s); } catch { return (null, 0); }
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return (text, (s.Length / 4) + 1);
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}
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}
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