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Faster soft implementation of smulh and umulh (#134)
* 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.
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@ -153,12 +153,30 @@ namespace ChocolArm64.Instruction
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public static long SMulHi128(long LHS, long RHS)
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{
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return (long)(BigInteger.Multiply(LHS, RHS) >> 64);
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bool LSign = (LHS < 0);
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bool RSign = (RHS < 0);
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long Result = (long)UMulHi128((ulong)(LSign ? -LHS : LHS), (ulong)(RSign ? -RHS : RHS));
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if (LSign != RSign && LHS != 0 && RHS != 0)
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return ~Result; //for negative results, hi 64-bits start at 0xFFF... and count back
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return Result;
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}
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public static ulong UMulHi128(ulong LHS, ulong RHS)
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{
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return (ulong)(BigInteger.Multiply(LHS, RHS) >> 64);
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//long multiplication
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//multiply 32 bits at a time in 64 bit, the result is what's carried over 64 bits.
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ulong LHigh = LHS >> 32;
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ulong LLow = LHS & 0xFFFFFFFF;
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ulong RHigh = RHS >> 32;
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ulong RLow = RHS & 0xFFFFFFFF;
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ulong Z2 = LLow * RLow;
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ulong T = LHigh * RLow + (Z2 >> 32);
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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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}
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