107 lines
4.3 KiB
C#
107 lines
4.3 KiB
C#
using System;
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using System.Text;
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namespace VAR.UrlCompressor
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{
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class Base62
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{
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private static string Base62CodingSpace = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
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public static string Encode(byte[] original)
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{
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StringBuilder sb = new StringBuilder();
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int bitPosition = 0;
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int lenght = original.Length * 8;
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while (bitPosition < lenght)
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{
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int pad = 0;
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if (bitPosition + 6 > lenght)
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{
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pad = lenght - (bitPosition + 6);
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}
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bool bit0 = original.ReadBit(bitPosition, 0 + pad);
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bool bit1 = original.ReadBit(bitPosition, 1 + pad);
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bool bit2 = original.ReadBit(bitPosition, 2 + pad);
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bool bit3 = original.ReadBit(bitPosition, 3 + pad);
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bool bit4 = original.ReadBit(bitPosition, 4 + pad);
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bool bit5 = original.ReadBit(bitPosition, 5 + pad);
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if (bit0 == true && bit1 == true && bit2 == true && bit3 == true && bit4 == true)
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{
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sb.Append(Base62CodingSpace[61]);
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bitPosition += 5;
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continue;
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}
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if (bit0 == true && bit1 == true && bit2 == true && bit3 == true && bit4 == false)
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{
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sb.Append(Base62CodingSpace[60]);
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bitPosition += 5;
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continue;
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}
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int charIdx = (bit0 ? 0x20 : 0) | (bit1 ? 0x10 : 0) | (bit2 ? 0x08 : 0) | (bit3 ? 0x04 : 0) | (bit4 ? 0x02 : 0) | (bit5 ? 0x01 : 0);
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sb.Append(Base62CodingSpace[charIdx]);
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bitPosition += 6;
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}
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return sb.ToString();
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}
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public static byte[] Decode(string base62)
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{
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byte[] bytes = new byte[base62.Length * 6 / 8];
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int bitPosition = 0;
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for (int i = 0; i < base62.Length; i++)
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{
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int charIdx = Base62CodingSpace.IndexOf(base62[i]);
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if ((i + 1) == base62.Length)
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{
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// Last symbol
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int rest = 8 - (bitPosition % 8);
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if (rest == 8) { throw new Exception("Extra symbol at end"); }
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if ((charIdx >> rest) > 0) { throw new Exception("Invalid ending symbol"); }
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int pad = 6 - rest;
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bytes.WriteBit(bitPosition, 0 - pad, (charIdx & 0x20) > 0);
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bytes.WriteBit(bitPosition, 1 - pad, (charIdx & 0x10) > 0);
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bytes.WriteBit(bitPosition, 2 - pad, (charIdx & 0x08) > 0);
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bytes.WriteBit(bitPosition, 3 - pad, (charIdx & 0x04) > 0);
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bytes.WriteBit(bitPosition, 4 - pad, (charIdx & 0x02) > 0);
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bytes.WriteBit(bitPosition, 5 - pad, (charIdx & 0x01) > 0);
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break;
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}
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if (charIdx == 60)
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{
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bytes.WriteBit(bitPosition, 0, true);
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bytes.WriteBit(bitPosition, 1, true);
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bytes.WriteBit(bitPosition, 2, true);
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bytes.WriteBit(bitPosition, 3, true);
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bytes.WriteBit(bitPosition, 4, false);
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bitPosition += 5;
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}
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else if (charIdx == 61)
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{
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bytes.WriteBit(bitPosition, 0, true);
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bytes.WriteBit(bitPosition, 1, true);
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bytes.WriteBit(bitPosition, 2, true);
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bytes.WriteBit(bitPosition, 3, true);
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bytes.WriteBit(bitPosition, 4, true);
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bitPosition += 5;
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}
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else
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{
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bytes.WriteBit(bitPosition, 0, (charIdx & 0x20) > 0);
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bytes.WriteBit(bitPosition, 1, (charIdx & 0x10) > 0);
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bytes.WriteBit(bitPosition, 2, (charIdx & 0x08) > 0);
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bytes.WriteBit(bitPosition, 3, (charIdx & 0x04) > 0);
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bytes.WriteBit(bitPosition, 4, (charIdx & 0x02) > 0);
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bytes.WriteBit(bitPosition, 5, (charIdx & 0x01) > 0);
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bitPosition += 6;
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}
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}
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return bytes;
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}
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}
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}
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