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And=> xor, powerOfTwoToHighByte to const

This commit is contained in:
Ben Adams 2016-10-16 21:58:49 +01:00
parent 97d4406614
commit 00a63537cf
1 changed files with 10 additions and 7 deletions
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17
src/Microsoft.AspNetCore.Server.Kestrel/Internal/Infrastructure/MemoryPoolIterator.cs
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@ -11,7 +11,14 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Internal.Infrastructure
{
public struct MemoryPoolIterator
{
private static readonly ulong _powerOfTwoToHighByte = PowerOfTwoToHighByte();
private const ulong _xorPowerOfTwoToHighByte = (0x07ul |
0x06ul << 8 |
0x05ul << 16 |
0x04ul << 24 |
0x03ul << 32 |
0x02ul << 40 |
0x01ul << 48 ) + 1;
private static readonly int _vectorSpan = Vector<byte>.Count;
private MemoryPoolBlock _block;
@ -785,9 +792,9 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Internal.Infrastructure
}
// Flag least significant power of two bit
var powerOfTwoFlag = (ulong)(longValue & -longValue);
var powerOfTwoFlag = (ulong)(longValue ^ (longValue - 1));
// Shift all powers of two into the high byte and extract
var foundByteIndex = (int)((powerOfTwoFlag * _powerOfTwoToHighByte) >> 61);
var foundByteIndex = (int)((powerOfTwoFlag * _xorPowerOfTwoToHighByte) >> 57);
// Single LEA instruction with jitted const (using function result)
return i * 8 + foundByteIndex;
}
@ -1044,9 +1051,5 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Internal.Infrastructure
return Vector.AsVectorByte(new Vector<ulong>(vectorByte * 0x0101010101010101ul));
}
private static ulong PowerOfTwoToHighByte()
{
return BitConverter.IsLittleEndian ? 0x20406080A0C0E0ul : 0xE0C0A080604020ul;
}
}
}