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// AtomicF{32,64} implementation based on AtomicU{32,64}.
//
// This module provides atomic float implementations using atomic integer.
//
// Note that most of `fetch_*` operations of atomic floats are implemented using
// CAS loops, which can be slower than equivalent operations of atomic integers.
//
// GPU targets have atomic instructions for float, so GPU targets will use
// architecture-specific implementations instead of this implementation in the
// future: https://github.com/taiki-e/portable-atomic/issues/34
#![cfg_attr(
all(target_pointer_width = "16", not(feature = "fallback")),
allow(unused_imports, unused_macros)
)]
use core::{cell::UnsafeCell, sync::atomic::Ordering};
macro_rules! atomic_float {
(
$atomic_type:ident,
$float_type:ident,
$atomic_int_type:ident,
$int_type:ident,
$align:literal
) => {
#[repr(C, align($align))]
pub(crate) struct $atomic_type {
v: UnsafeCell<$float_type>,
}
// Send is implicitly implemented.
// SAFETY: any data races are prevented by atomic operations.
unsafe impl Sync for $atomic_type {}
impl $atomic_type {
#[inline]
pub(crate) const fn new(v: $float_type) -> Self {
Self { v: UnsafeCell::new(v) }
}
#[inline]
pub(crate) fn is_lock_free() -> bool {
crate::$atomic_int_type::is_lock_free()
}
#[inline]
pub(crate) const fn is_always_lock_free() -> bool {
crate::$atomic_int_type::is_always_lock_free()
}
#[inline]
pub(crate) fn get_mut(&mut self) -> &mut $float_type {
// SAFETY: the mutable reference guarantees unique ownership.
// (UnsafeCell::get_mut requires Rust 1.50)
unsafe { &mut *self.v.get() }
}
#[inline]
pub(crate) fn into_inner(self) -> $float_type {
self.v.into_inner()
}
#[inline]
#[cfg_attr(
any(all(debug_assertions, not(portable_atomic_no_track_caller)), miri),
track_caller
)]
pub(crate) fn load(&self, order: Ordering) -> $float_type {
$float_type::from_bits(self.as_bits().load(order))
}
#[inline]
#[cfg_attr(
any(all(debug_assertions, not(portable_atomic_no_track_caller)), miri),
track_caller
)]
pub(crate) fn store(&self, val: $float_type, order: Ordering) {
self.as_bits().store(val.to_bits(), order)
}
const_fn! {
const_if: #[cfg(not(portable_atomic_no_const_raw_ptr_deref))];
#[inline]
pub(crate) const fn as_bits(&self) -> &crate::$atomic_int_type {
// SAFETY: $atomic_type and $atomic_int_type have the same layout,
// and there is no concurrent access to the value that does not go through this method.
unsafe { &*(self as *const Self as *const crate::$atomic_int_type) }
}
}
#[inline]
pub(crate) const fn as_ptr(&self) -> *mut $float_type {
self.v.get()
}
}
cfg_has_atomic_cas! {
impl $atomic_type {
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub(crate) fn swap(&self, val: $float_type, order: Ordering) -> $float_type {
$float_type::from_bits(self.as_bits().swap(val.to_bits(), order))
}
#[inline]
#[cfg_attr(
any(all(debug_assertions, not(portable_atomic_no_track_caller)), miri),
track_caller
)]
pub(crate) fn compare_exchange(
&self,
current: $float_type,
new: $float_type,
success: Ordering,
failure: Ordering,
) -> Result<$float_type, $float_type> {
match self.as_bits().compare_exchange(
current.to_bits(),
new.to_bits(),
success,
failure,
) {
Ok(v) => Ok($float_type::from_bits(v)),
Err(v) => Err($float_type::from_bits(v)),
}
}
#[inline]
#[cfg_attr(
any(all(debug_assertions, not(portable_atomic_no_track_caller)), miri),
track_caller
)]
pub(crate) fn compare_exchange_weak(
&self,
current: $float_type,
new: $float_type,
success: Ordering,
failure: Ordering,
) -> Result<$float_type, $float_type> {
match self.as_bits().compare_exchange_weak(
current.to_bits(),
new.to_bits(),
success,
failure,
) {
Ok(v) => Ok($float_type::from_bits(v)),
Err(v) => Err($float_type::from_bits(v)),
}
}
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub(crate) fn fetch_add(&self, val: $float_type, order: Ordering) -> $float_type {
self.fetch_update_(order, |x| x + val)
}
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub(crate) fn fetch_sub(&self, val: $float_type, order: Ordering) -> $float_type {
self.fetch_update_(order, |x| x - val)
}
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
fn fetch_update_<F>(&self, order: Ordering, mut f: F) -> $float_type
where
F: FnMut($float_type) -> $float_type,
{
// This is a private function and all instances of `f` only operate on the value
// loaded, so there is no need to synchronize the first load/failed CAS.
let mut prev = self.load(Ordering::Relaxed);
loop {
let next = f(prev);
match self.compare_exchange_weak(prev, next, order, Ordering::Relaxed) {
Ok(x) => return x,
Err(next_prev) => prev = next_prev,
}
}
}
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub(crate) fn fetch_max(&self, val: $float_type, order: Ordering) -> $float_type {
self.fetch_update_(order, |x| x.max(val))
}
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub(crate) fn fetch_min(&self, val: $float_type, order: Ordering) -> $float_type {
self.fetch_update_(order, |x| x.min(val))
}
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub(crate) fn fetch_neg(&self, order: Ordering) -> $float_type {
const NEG_MASK: $int_type = !0 / 2 + 1;
$float_type::from_bits(self.as_bits().fetch_xor(NEG_MASK, order))
}
#[inline]
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
pub(crate) fn fetch_abs(&self, order: Ordering) -> $float_type {
const ABS_MASK: $int_type = !0 / 2;
$float_type::from_bits(self.as_bits().fetch_and(ABS_MASK, order))
}
}
} // cfg_has_atomic_cas!
};
}
cfg_has_atomic_32! {
atomic_float!(AtomicF32, f32, AtomicU32, u32, 4);
}
cfg_has_atomic_64! {
atomic_float!(AtomicF64, f64, AtomicU64, u64, 8);
}
|
