generic_atomics/

atomic_float_wrapper.rs

use atomic_traits::{
    fetch::{And, Nand, Or, Update, Xor},
    AsPtr, Atomic, Bitwise, FromPtr,
};
use core::{
    cell::UnsafeCell,
    ops::Not,
    sync::atomic::{AtomicU32, AtomicU64, Ordering},
};
use num_primitive::PrimitiveFloat;
use num_traits::FromPrimitive;

pub trait BitsAssociatedAtomic {
    type F: PrimitiveFloat;
    type AU: Atomic<Type = <Self::F as PrimitiveFloat>::Bits>
        + Bitwise
        + Update<Type = <Self::F as PrimitiveFloat>::Bits>
        + AsPtr
        + FromPtr;
}

impl BitsAssociatedAtomic for u32 {
    type AU = AtomicU32;
    type F = f32;
}

impl BitsAssociatedAtomic for u64 {
    type AU = AtomicU64;
    type F = f64;
}

#[repr(transparent)]
pub struct AtomicFloatWrapper<F: PrimitiveFloat>(UnsafeCell<F>);

// SAFETY: We only ever access the underlying data by refcasting to AtomicU32,
// which guarantees no data races.
#[expect(unsafe_code)]
unsafe impl<F: PrimitiveFloat> Send for AtomicFloatWrapper<F> {}
#[expect(unsafe_code)]
unsafe impl<F: PrimitiveFloat> Sync for AtomicFloatWrapper<F> {}

// Static assertions that the layout is identical, we cite these in a safety
// comment in `AtomicF32::atom()`. Note that the alignment check is stricter
// than we need, as it would still be safe if `AtomicU32` is less strictly-
// aligned than our `f32`. Unlike with `AtomicF64`, this is unlikely to occur.
const _: [(); core::mem::size_of::<AtomicU32>()] = [(); core::mem::size_of::<UnsafeCell<f32>>()];
const _: [(); core::mem::align_of::<AtomicU32>()] = [(); core::mem::align_of::<UnsafeCell<f32>>()];

impl<F, U> AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    #[inline]
    pub const fn new(float: F) -> Self {
        Self(UnsafeCell::new(float))
    }

    #[inline]
    fn as_atomic_bits(&self) -> &<F::Bits as BitsAssociatedAtomic>::AU {
        // Safety: All potentially shared reads/writes go through this, and the
        // static assertions above ensure that AtomicU32 and UnsafeCell<f32> are
        // compatible as pointers.
        let ptr_inner = &raw const self.0;
        let cast_ptr = ptr_inner.cast::<<F::Bits as BitsAssociatedAtomic>::AU>();
        #[expect(unsafe_code)]
        unsafe {
            &*cast_ptr
        }
    }
}

pub trait Abs {
    type Type;
    fn fetch_abs(&self, order: Ordering) -> Self::Type;
}

impl<F, U> Abs for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn fetch_abs(&self, order: Ordering) -> F {
        // nu = 0x7fff_ffff
        let mz: F = F::from_f32(-0f32).expect("infallible");
        let nu = mz.to_bits().not();
        let value = self.as_atomic_bits().fetch_and(nu, order);
        F::from_bits(value)
    }
}

pub trait Neg {
    type Type;
    fn fetch_neg(&self, order: Ordering) -> Self::Type;
}

impl<F, U> Neg for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn fetch_neg(&self, order: Ordering) -> F {
        // u  = 0x80000000
        let mz: F = F::from_f32(-0f32).expect("infallible");
        let u: U = mz.to_bits();

        F::from_bits(self.as_atomic_bits().fetch_xor(u, order))
    }
}

trait UseAtomicUpdate: atomic_traits::fetch::Update {
    fn update_with<F>(&self, order: Ordering, update: F) -> Self::Type
    where
        F: FnMut(Self::Type) -> Self::Type;
}

impl<F, U> UseAtomicUpdate for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    #[inline]
    fn update_with<Fun>(&self, order: Ordering, mut update: Fun) -> Self::Type
    where
        Fun: FnMut(Self::Type) -> Self::Type,
    {
        self.fetch_update(order, fail_order_for(order), |f| Some(update(f)))
            .expect("infallible")
    }
}

pub trait UseUpdateToAdd {
    type Type;
    fn fetch_add_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type;
}

impl<F, U> UseUpdateToAdd for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline(always)]
    fn fetch_add_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type {
        self.update_with(order, |f| f + val)
    }
}

pub trait UseUpdateToSub {
    type Type;
    fn fetch_sub_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type;
}

impl<F, U> UseUpdateToSub for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline(always)]
    fn fetch_sub_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type {
        self.update_with(order, |f| f - val)
    }
}

pub trait UseUpdateToMin {
    type Type;
    fn fetch_min_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type;
}

impl<F, U> UseUpdateToMin for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline(always)]
    fn fetch_min_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type {
        self.update_with(order, |f| f.min(val))
    }
}

pub trait UseUpdateToMax {
    type Type;
    fn fetch_max_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type;
}

impl<F, U> UseUpdateToMax for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline(always)]
    fn fetch_max_via_update(&self, val: Self::Type, order: Ordering) -> Self::Type {
        self.update_with(order, |f| f.max(val))
    }
}

impl<F, U> Atomic for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn new(float: F) -> Self {
        Self(UnsafeCell::new(float))
    }

    #[inline]
    fn get_mut(&mut self) -> &mut F {
        // SAFETY: the mutable reference guarantees unique ownership.
        let get = self.0.get();
        #[expect(unsafe_code)]
        unsafe {
            &mut *get
        }
    }

    #[inline]
    fn into_inner(self) -> F {
        self.0.into_inner()
    }

    #[inline]
    fn load(&self, ordering: Ordering) -> F {
        let value = self.as_atomic_bits().load(ordering);
        F::from_bits(value)
    }

    #[inline]
    fn store(&self, value: F, ordering: Ordering) {
        let val = value.to_bits();
        self.as_atomic_bits().store(val, ordering);
    }

    #[inline]
    fn swap(&self, new_value: F, ordering: Ordering) -> F {
        F::from_bits(self.as_atomic_bits().swap(new_value.to_bits(), ordering))
    }

    #[inline]
    #[expect(deprecated)]
    fn compare_and_swap(&self, current: F, new: F, order: Ordering) -> F {
        F::from_bits(self.as_atomic_bits().compare_and_swap(
            current.to_bits(),
            new.to_bits(),
            order,
        ))
    }

    #[inline]
    fn compare_exchange(
        &self,
        current: F,
        new: F,
        success: Ordering,
        failure: Ordering,
    ) -> Result<F, F> {
        let current1 = current.to_bits();
        let bits = new.to_bits();
        convert_result(
            self.as_atomic_bits()
                .compare_exchange(current1, bits, success, failure),
        )
    }

    #[inline]
    fn compare_exchange_weak(
        &self,
        current: F,
        new: F,
        success: Ordering,
        failure: Ordering,
    ) -> Result<F, F> {
        convert_result(self.as_atomic_bits().compare_exchange_weak(
            current.to_bits(),
            new.to_bits(),
            success,
            failure,
        ))
    }
}

impl<F, U> Update for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn fetch_update<Fun>(
        &self,
        set_order: Ordering,
        fetch_order: Ordering,
        mut update: Fun,
    ) -> Result<F, F>
    where
        Fun: FnMut(F) -> Option<F>,
    {
        let atomic_bits = self.as_atomic_bits();
        let res = U::AU::fetch_update(atomic_bits, set_order, fetch_order, |prev| {
            update(F::from_bits(prev)).map(F::to_bits)
        });
        convert_result(res)
    }
}

impl<F, U> Bitwise for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
}

impl<F, U> And for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn fetch_and(&self, val: F, order: Ordering) -> F {
        let val = F::to_bits(val);
        let r = self.as_atomic_bits().fetch_and(val, order);
        F::from_bits(r)
    }
}

impl<F, U> Nand for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn fetch_nand(&self, val: F, order: Ordering) -> F {
        let val = F::to_bits(val);
        let r = self.as_atomic_bits().fetch_nand(val, order);
        F::from_bits(r)
    }
}

impl<F, U> Or for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn fetch_or(&self, val: F, order: Ordering) -> F {
        let val = F::to_bits(val);
        let r = self.as_atomic_bits().fetch_or(val, order);
        F::from_bits(r)
    }
}

impl<F, U> Xor for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    type Type = F;

    #[inline]
    fn fetch_xor(&self, val: F, order: Ordering) -> F {
        let val = F::to_bits(val);
        let r = self.as_atomic_bits().fetch_xor(val, order);
        F::from_bits(r)
    }
}

impl<F, U> FromPtr for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    #[inline(always)]
    #[expect(unsafe_code)]
    unsafe fn from_ptr<'a>(ptr: *mut F) -> &'a Self {
        let ptr_u = ptr.cast::<U>();
        let ref_atomic_u: &<U as BitsAssociatedAtomic>::AU = unsafe { U::AU::from_ptr(ptr_u) };
        let ptr_atomic_u = core::ptr::from_ref::<<U as BitsAssociatedAtomic>::AU>(ref_atomic_u);
        let ptr_t = ptr_atomic_u.cast::<Self>();
        unsafe { &*ptr_t }
    }
}

impl<F, U> AsPtr for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    #[inline(always)]
    fn as_ptr(&self) -> *mut F {
        let src = self.as_atomic_bits().as_ptr();
        src.cast::<F>()
    }
}

impl<F, U> Default for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    #[inline(always)]
    fn default() -> Self {
        Self(UnsafeCell::new(F::default()))
    }
}

impl<F, U> core::fmt::Debug for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        core::fmt::Debug::fmt(&self.load(Ordering::SeqCst), f)
    }
}

impl<F, U> From<f32> for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    #[inline]
    fn from(f: f32) -> Self {
        Self::new(F::from_f32(f).expect("infallible"))
    }
}

impl<F, U> From<f64> for AtomicFloatWrapper<F>
where
    F: PrimitiveFloat<Bits = U> + FromPrimitive,
    U: BitsAssociatedAtomic<F = F> + Not<Output = U>,
{
    #[inline(always)]
    fn from(f: f64) -> Self {
        Self::new(F::from_f64(f).expect("infallible"))
    }
}

#[inline(always)]
fn convert_result<F: PrimitiveFloat>(r: Result<F::Bits, F::Bits>) -> Result<F, F> {
    r.map(F::from_bits).map_err(F::from_bits)
}

#[inline]
fn fail_order_for(order: Ordering) -> Ordering {
    match order {
        Ordering::Release | Ordering::Relaxed => Ordering::Relaxed,
        Ordering::Acquire | Ordering::AcqRel => Ordering::Acquire,
        Ordering::SeqCst => Ordering::SeqCst,
        o => unreachable!("Unknown ordering: {:?} (file a bug with atomic_float)", o),
    }
}