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Code Issues 975 Packages Projects Releases 25 Wiki Activity

Rar: Fix CPU performance regression

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This commit is contained in:
Julian Xhokaxhiu
2026-08-04 19:56:17 +02:00
parent 26c17975a6
commit e4cc79f252
1 changed files with 8 additions and 31 deletions
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39
src/SharpCompress/Compressors/Rar/RarCRC.cs
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@@ -1,10 +1,16 @@
using System;
using SharpCompress.Crypto;
namespace SharpCompress.Compressors.Rar;
internal static class RarCRC
{
private static readonly uint[] crcTab;
// Reuse Crc32Stream's cached slice-by-16 table (same polynomial) instead of a separate
// byte-at-a-time table, so bulk CRC checks during Rar extraction get the same throughput
// as Zip/GZip/7Zip/LZip CRC32 validation instead of a much slower one-byte-per-iteration loop.
private static readonly uint[] crcTab = Crc32Stream.InitializeTable(
Crc32Stream.DEFAULT_POLYNOMIAL
);
public static uint CheckCrc(uint startCrc, byte b) =>
(crcTab[((int)startCrc ^ b) & 0xff] ^ (startCrc >> 8));
@@ -12,35 +18,6 @@ internal static class RarCRC
public static uint CheckCrc(uint startCrc, ReadOnlySpan<byte> data, int offset, int count)
{
var size = Math.Min(data.Length - offset, count);
for (var i = 0; i < size; i++)
{
startCrc = (crcTab[((int)startCrc ^ data[offset + i]) & 0xff] ^ (startCrc >> 8));
}
return (startCrc);
}
static RarCRC()
{
{
crcTab = new uint[256];
for (uint i = 0; i < 256; i++)
{
var c = i;
for (var j = 0; j < 8; j++)
{
if ((c & 1) != 0)
{
c >>= 1;
c ^= 0xEDB88320;
}
else
{
c >>= 1;
}
}
crcTab[i] = c;
}
}
return Crc32Stream.CalculateCrc(crcTab, startCrc, data.Slice(offset, size));
}
}