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BitOperations arm64 intrinsic for LeadingZeroCount, TrailingZeroCount and Log2 #34486

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merged 5 commits into from
Apr 4, 2020
Merged

BitOperations arm64 intrinsic for LeadingZeroCount, TrailingZeroCount and Log2 #34486

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cc04050
ARM64 intrinsic for LeadingZeroCount
kunalspathak Apr 3, 2020
90be48c
ARM64 intrinsic for Log2
kunalspathak Apr 3, 2020
a2effc7
ARM64 intrinsic for TrailingZeroCount
kunalspathak Apr 3, 2020
cdf34f9
Remove redundant cast
kunalspathak Apr 3, 2020
80ff885
Add entry of System.Runtime.Intrinsic.Arm in shim
kunalspathak Apr 3, 2020
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54 changes: 42 additions & 12 deletions src/libraries/System.Private.CoreLib/src/System/Numerics/BitOperations.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Intrinsics.X86;
using System.Runtime.Intrinsics.Arm;
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#if SYSTEM_PRIVATE_CORELIB
using Internal.Runtime.CompilerServices;
Expand Down Expand Up @@ -61,6 +62,11 @@ public static int LeadingZeroCount(uint value)
return (int)Lzcnt.LeadingZeroCount(value);
}

if (ArmBase.IsSupported)
{
return (int)ArmBase.LeadingZeroCount(value);
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}

// Unguarded fallback contract is 0->31
if (value == 0)
{
Expand All @@ -85,6 +91,11 @@ public static int LeadingZeroCount(ulong value)
return (int)Lzcnt.X64.LeadingZeroCount(value);
}

if (ArmBase.Arm64.IsSupported)
{
return (int)ArmBase.Arm64.LeadingZeroCount(value);
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}

uint hi = (uint)(value >> 32);

if (hi == 0)
Expand All @@ -104,6 +115,12 @@ public static int LeadingZeroCount(ulong value)
[CLSCompliant(false)]
public static int Log2(uint value)
{
// Enforce conventional contract 0->0 (Log(0) is undefined)
if (value == 0)
{
return 0;
}

// value lzcnt actual expected
// ..0000 32 0 0 (by convention, guard clause)
// ..0001 31 31-31 0
Expand All @@ -113,16 +130,15 @@ public static int Log2(uint value)
// 1000.. 0 31-0 31
if (Lzcnt.IsSupported)
{
// Enforce conventional contract 0->0 (Log(0) is undefined)
if (value == 0)
{
return 0;
}

// LZCNT contract is 0->32
return 31 - (int)Lzcnt.LeadingZeroCount(value);
}

if (ArmBase.IsSupported)
{
return 31 - (int)ArmBase.LeadingZeroCount(value);
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}

// Fallback contract is 0->0
return Log2SoftwareFallback(value);
}
Expand All @@ -136,18 +152,23 @@ public static int Log2(uint value)
[CLSCompliant(false)]
public static int Log2(ulong value)
{
if (Lzcnt.X64.IsSupported)
// Enforce conventional contract 0->0 (Log(0) is undefined)
if (value == 0)
{
// Enforce conventional contract 0->0 (Log(0) is undefined)
if (value == 0)
{
return 0;
}
return 0;
}

if (Lzcnt.X64.IsSupported)
{
// LZCNT contract is 0->64
return 63 - (int)Lzcnt.X64.LeadingZeroCount(value);
}

if (ArmBase.Arm64.IsSupported)
{
return 63 - (int)ArmBase.Arm64.LeadingZeroCount(value);
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}

uint hi = (uint)(value >> 32);

if (hi == 0)
Expand Down Expand Up @@ -275,6 +296,11 @@ public static int TrailingZeroCount(uint value)
return (int)Bmi1.TrailingZeroCount(value);
}

if (ArmBase.IsSupported)
{
return (int)ArmBase.LeadingZeroCount(ArmBase.ReverseElementBits(value));
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}

// Unguarded fallback contract is 0->0
if (value == 0)
{
Expand Down Expand Up @@ -313,6 +339,10 @@ public static int TrailingZeroCount(ulong value)
return (int)Bmi1.X64.TrailingZeroCount(value);
}

if (ArmBase.Arm64.IsSupported)
{
return (int)ArmBase.Arm64.LeadingZeroCount(ArmBase.Arm64.ReverseElementBits(value));
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}
uint lo = (uint)value;

if (lo == 0)
Expand Down