[Arm64] MultiplyHigh #43106
Description
Exposing smulh/umulh as intrinsics on Arm64
class ArmBase.Arm64
{
/// <summary>
/// A64: SMULH Xd, Xn, Xm
/// </summary>
public static long MultiplyHigh(long left, long right);
/// <summary>
/// A64: UMULH Xd, Xn, Xm
/// </summary>
public static ulong MultiplyHigh(ulong left, ulong right);
}would allow to implement System.Math.BigMul as
low = a * b;
return ArmBase.Arm64.MultiplyHigh(a, b);