Make algebraic functions into const fn items.

[bjoernager]

Tracking issue: #136469

This PR makes the algebraic intrinsics and the unstable, algebraic functions of f16, f32, f64, and f128 into const fn items:

impl f16 {
    pub const fn algebraic_add(self, rhs: f16) -> f16;
    pub const fn algebraic_sub(self, rhs: f16) -> f16;
    pub const fn algebraic_mul(self, rhs: f16) -> f16;
    pub const fn algebraic_div(self, rhs: f16) -> f16;
    pub const fn algebraic_rem(self, rhs: f16) -> f16;
}

impl f32 {
    pub const fn algebraic_add(self, rhs: f32) -> f32;
    pub const fn algebraic_sub(self, rhs: f32) -> f32;
    pub const fn algebraic_mul(self, rhs: f32) -> f32;
    pub const fn algebraic_div(self, rhs: f32) -> f32;
    pub const fn algebraic_rem(self, rhs: f32) -> f32;
}

impl f64 {
    pub const fn algebraic_add(self, rhs: f64) -> f64;
    pub const fn algebraic_sub(self, rhs: f64) -> f64;
    pub const fn algebraic_mul(self, rhs: f64) -> f64;
    pub const fn algebraic_div(self, rhs: f64) -> f64;
    pub const fn algebraic_rem(self, rhs: f64) -> f64;
}

impl f128 {
    pub const fn algebraic_add(self, rhs: f128) -> f128;
    pub const fn algebraic_sub(self, rhs: f128) -> f128;
    pub const fn algebraic_mul(self, rhs: f128) -> f128;
    pub const fn algebraic_div(self, rhs: f128) -> f128;
    pub const fn algebraic_rem(self, rhs: f128) -> f128;
}

// core::intrinsics

pub const fn fadd_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn fsub_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn fmul_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn fdiv_algebraic<T: Copy>(a: T, b: T) -> T;
pub const fn frem_algebraic<T: Copy>(a: T, b: T) -> T;

This PR does not preserve the initial behaviour of these functions yielding non-deterministic output under Miri; it is most likely desired to reimplement this behaviour at some point.

[rustbot]

r? @thomcc

rustbot has assigned @thomcc.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[rustbot]

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

The Miri subtree was changed

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

[bjoernager]

@rustbot label +T-libs-api -T-libs

[RalfJung]

r? @RalfJung

Cc @rust-lang/wg-const-eval @rust-lang/lang -- this unstably makes some intrinsics const-callable. I think we only need FCP once they become callable on stable, but pinging you anyway to put this on your radar.

[RalfJung]

Looking good, thanks!

@bors r+ rollup

[bors]

📌 Commit 0296f05 has been approved by RalfJung

It is now in the queue for this repository.