Improve CountLeadingZeros() algorithm, nits. (#219)
* Update AInstEmitSimdArithmetic.cs * Update ASoftFallback.cs * Update ASoftFallback.cs * Update ASoftFallback.cs * Update AInstEmitSimdArithmetic.cs
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2 changed files with 37 additions and 13 deletions
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@ -101,11 +101,13 @@ namespace ChocolArm64.Instruction
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int Bytes = Op.GetBitsCount() >> 3;
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int Elems = Bytes >> Op.Size;
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int ESize = 8 << Op.Size;
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for (int Index = 0; Index < Elems; Index++)
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{
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EmitVectorExtractZx(Context, Op.Rn, Index, Op.Size);
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Context.EmitLdc_I4(8 << Op.Size);
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Context.EmitLdc_I4(ESize);
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Emit();
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@ -12,24 +12,44 @@ namespace ChocolArm64.Instruction
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public static ulong CountLeadingSigns(ulong Value, int Size)
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{
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return CountLeadingZeros((Value >> 1) ^ Value, Size - 1);
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}
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Value ^= Value >> 1;
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public static ulong CountLeadingZeros(ulong Value, int Size)
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{
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int HighBit = Size - 1;
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int HighBit = Size - 2;
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for (int Bit = HighBit; Bit >= 0; Bit--)
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{
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if (((Value >> Bit) & 1) != 0)
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if (((Value >> Bit) & 0b1) != 0)
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{
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return (ulong)(HighBit - Bit);
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}
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}
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return (ulong)(Size - 1);
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}
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private static readonly byte[] ClzNibbleTbl = { 4, 3, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0 };
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public static ulong CountLeadingZeros(ulong Value, int Size)
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{
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if (Value == 0)
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{
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return (ulong)Size;
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}
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int NibbleIdx = Size;
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int PreCount, Count = 0;
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do
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{
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NibbleIdx -= 4;
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PreCount = ClzNibbleTbl[(Value >> NibbleIdx) & 0b1111];
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Count += PreCount;
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}
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while (PreCount == 4);
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return (ulong)Count;
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}
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public static uint CountSetBits8(uint Value)
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{
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Value = ((Value >> 1) & 0x55) + (Value & 0x55);
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@ -168,9 +188,10 @@ namespace ChocolArm64.Instruction
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public static long SMulHi128(long LHS, long RHS)
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{
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long Result = (long)UMulHi128((ulong)(LHS), (ulong)(RHS));
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long Result = (long)UMulHi128((ulong)LHS, (ulong)RHS);
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if (LHS < 0) Result -= RHS;
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if (RHS < 0) Result -= LHS;
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return Result;
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}
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@ -187,6 +208,7 @@ namespace ChocolArm64.Instruction
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ulong Z1 = T & 0xFFFFFFFF;
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ulong Z0 = T >> 32;
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Z1 += LLow * RHigh;
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return LHigh * RHigh + Z0 + (Z1 >> 32);
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}
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}
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