Question

I wrote an Int128 type and it works great. I thought I could improve on its performance with a simple idea: Improve the shift operations which are a bit clumsy.

Because they are heavily used in multiplication and division, an improvement would have a ripple effect. So I began creating a dynamic method (to shift low and rotate high), only to discover that there are no OpCodes.Rol or OpCodes.Ror instructions.

Is this possible in IL?

Answer 1

No.

You need to implement it with bit shifts

UInt64 highBits = 0;
UInt64 lowBits = 1;
Int32 n = 63;
var altShift = (n - 63);

var lowShiftedOff = (n - 63) > 0 ? 0 : (lowBits << n);
var highShiftedOff = (n - 63) > 0 ? 0 : (highBits << n);

var highResult = (UInt64)(highShiftedOff | (altShift > 0 ? (lowBits << altShift - 1) : 0));
var lowResult= (UInt64)(lowShiftedOff | (altShift > 0 ? (highBits << altShift - 1) : 0));