SabreTools/SabreTools.Hashing
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Add fast no-reflect transform implementation

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This commit is contained in:
Matt Nadareski
2024-11-07 01:40:05 -05:00
parent 4eec52241e
commit e36cd9bf3c
1 changed files with 49 additions and 4 deletions
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53
SabreTools.Hashing/Crc/CrcTable.cs
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@@ -143,9 +143,9 @@ namespace SabreTools.Hashing.Crc
for (int b = 0; b < 8; b++)
{
if (_definition.ReflectIn)
hash = (hash >> _processBits) ^ _table[0, (byte)(hash & 1) ^ ((byte)(data[offset] >> b) & 1)];
hash = (hash >> 1) ^ _table[0, (byte)(hash & 1) ^ ((byte)(data[offset] >> b) & 1)];
else
hash = (hash << _processBits) ^ _table[0, (byte)((hash >> _bitShift) & 1) ^ ((byte)(data[offset] >> (7 - b)) & 1)];
hash = (hash << 1) ^ _table[0, (byte)((hash >> _bitShift) & 1) ^ ((byte)(data[offset] >> (7 - b)) & 1)];
}
}
@@ -153,9 +153,9 @@ namespace SabreTools.Hashing.Crc
else
{
if (_definition.ReflectIn)
hash = (hash >> _processBits) ^ _table[0, (byte)hash ^ data[offset]];
hash = (hash >> 8) ^ _table[0, (byte)hash ^ data[offset]];
else
hash = (hash << _processBits) ^ _table[0, ((byte)(hash >> _bitShift)) ^ data[offset]];
hash = (hash << 8) ^ _table[0, ((byte)(hash >> _bitShift)) ^ data[offset]];
}
}
@@ -174,6 +174,11 @@ namespace SabreTools.Hashing.Crc
TransformBlockFast32Reflect(ref hash, data, offset, length);
return true;
}
if (_definition.Width == 32 && !_definition.ReflectIn)
{
TransformBlockFast32NoReflect(ref hash, data, offset, length);
return true;
}
return false;
}
@@ -226,5 +231,45 @@ namespace SabreTools.Hashing.Crc
// Assign the new hash value
hash = local;
}
/// <summary>
/// Optimized transformation for 32-bit CRC with reflection
/// </summary>
private void TransformBlockFast32NoReflect(ref ulong hash, byte[] data, int offset, int length)
{
// Process on a copy of the hash
ulong local = hash;
// Process aligned data
if (length > 4)
{
long end = offset + (length & ~(uint)3);
length &= 3;
while (offset < end)
{
ulong low = local ^ (uint)(
(data[offset + 3] )
+ (data[offset + 2] << 8 )
+ (data[offset + 1] << 16)
+ (data[offset + 0] << 24));
offset += 4;
local = _table[0, (byte)(low )]
^ _table[1, (byte)(low >> 8 )]
^ _table[2, (byte)(low >> 16 )]
^ _table[3, (byte)(low >> 24 )];
}
}
// Process unaligned data
while (length-- != 0)
{
PerformChecksumStep(ref local, data, offset++);
}
// Assign the new hash value
hash = local;
}
}
}