Tracking Issue for Integer Funnel Shifts (original) (raw)
Feature gate: #![feature(funnel_shifts)]
This is a tracking issue for implementation of funnel shifts on integers.
Funnel shifts are essentially a generalization of bitwise rotations. a.funnel_shl(b, n) means concatenate a and b (with a in the most significant half), creating an integer twice as wide, shifting this to the left by n (taken modulo the bit size of a and b), shifting in zeros, and finally extract the most significant half of the wide integer as the result.
The functions will panic if n >= T::BITS, and the wrapping versions consider n modulo T::BITS. The unchecked variant doesn't do any checks (as the name suggests), and so is unsafe.
a.wrapping_funnel_shl(a, n) is meant to be exactly equivalent to a.rotate_left(n).
Public API
impl {u8, u16, u32, u64, u128, usize} { pub const fn funnel_shl(self, rhs: Self, shift: u32) -> Self; pub const fn funnel_shr(self, rhs: Self, shift: u32) -> Self;
pub const fn wrapping_funnel_shl(self, rhs: Self, shift: u32) -> Self;
pub const fn wrapping_funnel_shr(self, rhs: Self, shift: u32) -> Self;
pub const unsafe fn unchecked_funnel_shl(self, rhs: Self, shift: u32) -> Self;
pub const unsafe fn unchecked_funnel_shr(self, rhs: Self, shift: u32) -> Self;}
Steps / History
A SIMD version of these intrinsics were added in #142078
- Implementation
- Final comment period (FCP)1
- Stabilization PR
Unresolved Questions
- Should we also provide these functions on signed integer types (akin to
rotates)?