[Proposal]: New operator for rotate shift

[anchurcn]

New operator for rotate shift

• Proposed
• Prototype: Not Started
• Implementation: Not Started
• Specification: Not Started

Summary

Bits operation is common in primitive integers.
There have been SHR(Shift Right) operator and SHL(Shift Left) operator for unsigned integers.

uint value = 0xAABBCCDD;
uint output = value >> 8;
// output is 0x00AABBCC

Also SAR(Shift Arithmetic Right) operator and SAL(Shift Arithmetic Left) operator are for signed integers.

int value = (int)0xFFAABBCC;
int output = value >> 8;
// output is 0xFFFFAABB

But there are no operators for rotate shift operations.

Motivation

If we want transform 0xAABBCCDD into 0xDDAABBCC,
we need to write a long expression.

uint value = 0xAABBCCDD;
int nBits = sizeof(value) * 8;// value's width in bits
int n=8;// shift number of bits
uint output = (value << (nBits - n) | value >> n)
//output is 0xDDAABBCC

If new operators come, we have a more elegant way.
Assume >>> is a new operator for ROR(Rotate Right) operation.

uint value = 0xAABBCCDD;
uint output = value >>> 8;
// output is 0xDDAABBCC

Detailed design

IL may not have direct instructions for ROR or ROL, we can just express it as
(value << (nBits - n) | value >> n) or (value << (nBits - n) | value >> n) in IL.
But I think JIT compiler will generate the best assembly for the target platform.

Drawbacks

Alternatives

Unresolved questions

Design meetings

[CyrusNajmabadi]

This def feels like something a method could be exposed for. It could presumably be implemented by the jit with whatever smarts are needed.

[alexrp]

They even exist already: https://docs.microsoft.com/en-us/dotnet/api/system.numerics.bitoperations (and are recognized by the JIT)

[anchurcn]

Yes, method can help a lot. I have made some extension method for my project. But operator is better I think.