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Faster soft implementation of smulh and umulh (#134)

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* Faster soft implementation of smulh and umulh

* smulh: Fixed mul with 0 acting like it had a negative result.

* Use compliment for negative smulh result.
This commit is contained in:
riperiperi 2018-06-13 14:55:45 +01:00 committed by gdkchan
parent 36827c2355
commit afa5bf81e3
1 changed files with 20 additions and 2 deletions
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22
ChocolArm64/Instruction/ASoftFallback.cs
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@ -153,12 +153,30 @@ namespace ChocolArm64.Instruction
public static long SMulHi128(long LHS, long RHS) public static long SMulHi128(long LHS, long RHS)
{ {
return (long)(BigInteger.Multiply(LHS, RHS) >> 64); bool LSign = (LHS < 0);
bool RSign = (RHS < 0);
long Result = (long)UMulHi128((ulong)(LSign ? -LHS : LHS), (ulong)(RSign ? -RHS : RHS));
if (LSign != RSign && LHS != 0 && RHS != 0)
return ~Result; //for negative results, hi 64-bits start at 0xFFF... and count back
return Result;
} }
public static ulong UMulHi128(ulong LHS, ulong RHS) public static ulong UMulHi128(ulong LHS, ulong RHS)
{ {
return (ulong)(BigInteger.Multiply(LHS, RHS) >> 64); //long multiplication
//multiply 32 bits at a time in 64 bit, the result is what's carried over 64 bits.
ulong LHigh = LHS >> 32;
ulong LLow = LHS & 0xFFFFFFFF;
ulong RHigh = RHS >> 32;
ulong RLow = RHS & 0xFFFFFFFF;
ulong Z2 = LLow * RLow;
ulong T = LHigh * RLow + (Z2 >> 32);
ulong Z1 = T & 0xFFFFFFFF;
ulong Z0 = T >> 32;
Z1 += LLow * RHigh;
return LHigh * RHigh + Z0 + (Z1 >> 32);
} }
} }
} }