opus-rs 0.1.27

//! no_std / std compatibility shims — zero external dependencies.
//!
//! Provides:
//! * [`OnceCell`] — a dependency-free, **heap-free** lazy cell backed by a 3-state
//!   atomic and inline `UnsafeCell<MaybeUninit<T>>` storage. The value is
//!   constructed exactly once into the inline storage, so no global allocator is
//!   required. Replaces `std::sync::LazyLock`.
//! * [`x86_has_avx`] / [`x86_has_avx2`] — x86 SIMD availability probes. Under the
//!   `std` feature these use the OS-backed `is_x86_feature_detected!`; without `std`
//!   they fall back to compile-time `cfg!(target_feature = ...)`.

use core::cell::UnsafeCell;
use core::hint;
use core::mem::MaybeUninit;
use core::sync::atomic::{AtomicU8, Ordering};

// ---------------------------------------------------------------------------
// OnceCell (heap-free lazy initialization)
// ---------------------------------------------------------------------------

/// Lazily-initialized value stored in inline (non-heap) storage.
///
/// State machine encoded in [`AtomicU8`]:
/// * `0` — uninitialized, idle
/// * `1` — a thread is currently initializing
/// * `2` — initialization complete; the value is live
///
/// The stored value is constructed exactly once into the embedded
/// `MaybeUninit<T>` and never mutated afterwards. Publication uses `Release`
/// ordering so all field writes are visible to any reader that observes state `2`
/// with `Acquire` ordering.
pub struct OnceCell<T: Sync> {
    state: AtomicU8,
    storage: UnsafeCell<MaybeUninit<T>>,
}

// SAFETY: `OnceCell` hands out shared `&T` references to a value that is
// constructed once and never mutated. `T: Sync` makes shared access sound. The
// `UnsafeCell` is only ever written by the single initializer before publication.
unsafe impl<T: Sync> Sync for OnceCell<T> {}

impl<T: Sync> OnceCell<T> {
    /// Create a new, uninitialized cell. `const`-constructible so it can live in a
    /// `static`.
    pub const fn new() -> Self {
        Self {
            state: AtomicU8::new(0),
            storage: UnsafeCell::new(MaybeUninit::uninit()),
        }
    }

    /// Return a shared reference to the value, initializing it on first access.
    ///
    /// `init` is invoked at most once across all threads. It must not panic: a
    /// panic would leave the cell in the `initializing` (1) state and subsequent
    /// callers would spin indefinitely. In practice the only initializer used by
    /// this crate (`CeltMode::new_48000_960_120`) is infallible.
    pub fn get(&self, init: impl FnOnce() -> T) -> &T {
        if self.state.load(Ordering::Acquire) == 2 {
            // SAFETY: initialization is complete; storage holds a valid `T`.
            return unsafe { (*self.storage.get()).assume_init_ref() };
        }
        self.get_slow(init)
    }

    #[cold]
    fn get_slow(&self, init: impl FnOnce() -> T) -> &T {
        // Spin until we either claim the initializer slot (0 -> 1) or observe a
        // finished initialization.
        while self
            .state
            .compare_exchange(0, 1, Ordering::Acquire, Ordering::Relaxed)
            .is_err()
        {
            if self.state.load(Ordering::Acquire) == 2 {
                // SAFETY: another thread finished initialization.
                return unsafe { (*self.storage.get()).assume_init_ref() };
            }
            hint::spin_loop();
        }

        // We claimed the slot; construct into the inline storage and publish.
        // SAFETY: we are the sole writer (state == 1); no reader can observe the
        // storage until we publish state == 2 with Release ordering.
        unsafe {
            (*self.storage.get()).write(init());
        }
        self.state.store(2, Ordering::Release);
        // SAFETY: initialization is complete and published.
        unsafe { (*self.storage.get()).assume_init_ref() }
    }
}

impl<T: Sync> Default for OnceCell<T> {
    fn default() -> Self {
        Self::new()
    }
}

// ---------------------------------------------------------------------------
// No-std slice sorting (`alloc` provides `[T]::sort*` as inherent methods; since
// this crate does not depend on `alloc`, we provide small insertion sorts here).
// ---------------------------------------------------------------------------

/// Sort a slice by a comparator (insertion sort). Intended for the small slices
/// used in this crate (energy bands, NLSF coefficients, median-of-3/5); O(n²) is
/// fine because `n` is tiny.
pub fn sort_by<T>(slice: &mut [T], mut cmp: impl FnMut(&T, &T) -> core::cmp::Ordering) {
    for i in 1..slice.len() {
        let mut j = i;
        while j > 0 && cmp(&slice[j - 1], &slice[j]) == core::cmp::Ordering::Greater {
            slice.swap(j - 1, j);
            j -= 1;
        }
    }
}

/// Sort a slice in ascending order (`Ord` version). See [`sort_by`].
pub fn sort<T: Ord>(slice: &mut [T]) {
    sort_by(slice, |a, b| a.cmp(b));
}

// ---------------------------------------------------------------------------
// x86 SIMD feature detection
// ---------------------------------------------------------------------------

/// Whether the `avx` x86 feature is usable.
///
/// * With the `std` feature: OS-backed runtime detection via CPUID.
/// * Without `std`: compile-time detection (`cfg!(target_feature = "avx")`); build
///   with e.g. `RUSTFLAGS="-C target-feature=+avx"` to enable it.
#[cfg(all(feature = "std", target_arch = "x86_64"))]
pub fn x86_has_avx() -> bool {
    std::arch::is_x86_feature_detected!("avx")
}
#[cfg(not(all(feature = "std", target_arch = "x86_64")))]
#[allow(dead_code)]
pub fn x86_has_avx() -> bool {
    cfg!(target_feature = "avx")
}

/// Whether the `avx2` x86 feature is usable. See [`x86_has_avx`].
#[cfg(all(feature = "std", target_arch = "x86_64"))]
pub fn x86_has_avx2() -> bool {
    std::arch::is_x86_feature_detected!("avx2")
}
#[cfg(not(all(feature = "std", target_arch = "x86_64")))]
#[allow(dead_code)]
pub fn x86_has_avx2() -> bool {
    cfg!(target_feature = "avx2")
}

// ---------------------------------------------------------------------------
// Float math (no_std needs libm for transcendentals / rounding)
// ---------------------------------------------------------------------------

#[cfg(not(feature = "std"))]
#[cfg(not(feature = "libm"))]
compile_error!(
    "opus-rs no_std builds require the `libm` feature (or the `std` feature). \
     Set features = [\"libm\"] (or re-enable default-features)."
);

/// Extension trait giving `f32`/`f64` the usual math methods (`sqrt`, `sin`, ...)
/// under `no_std` by forwarding to `libm`. Under the `std` feature the inherent
/// methods take priority and this trait is simply unused.
///
/// Bring it into scope with `use crate::compat::Math;` in any module that calls
/// these methods so the same `x.sqrt()` syntax works in both build modes.
#[cfg(all(not(feature = "std"), feature = "libm"))]
#[allow(dead_code)]
pub trait Math {
    fn sqrt(self) -> Self;
    fn floor(self) -> Self;
    fn ceil(self) -> Self;
    fn round(self) -> Self;
    fn trunc(self) -> Self;
    fn fract(self) -> Self;
    fn abs(self) -> Self;
    fn ln(self) -> Self;
    fn log2(self) -> Self;
    fn log10(self) -> Self;
    fn log(self, base: Self) -> Self;
    fn exp(self) -> Self;
    fn exp2(self) -> Self;
    fn powf(self, n: Self) -> Self;
    fn powi(self, n: i32) -> Self;
    fn sin(self) -> Self;
    fn cos(self) -> Self;
    fn tan(self) -> Self;
    fn atan2(self, other: Self) -> Self;
    fn atan(self) -> Self;
    fn asin(self) -> Self;
    fn acos(self) -> Self;
    fn sinh(self) -> Self;
    fn cosh(self) -> Self;
    fn tanh(self) -> Self;
    fn cbrt(self) -> Self;
    fn hypot(self, other: Self) -> Self;
    fn mul_add(self, a: Self, b: Self) -> Self;
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
impl Math for f32 {
    fn sqrt(self) -> Self {
        libm::sqrtf(self)
    }
    fn floor(self) -> Self {
        libm::floorf(self)
    }
    fn ceil(self) -> Self {
        libm::ceilf(self)
    }
    fn round(self) -> Self {
        libm::roundf(self)
    }
    fn trunc(self) -> Self {
        libm::truncf(self)
    }
    fn fract(self) -> Self {
        self - libm::truncf(self)
    }
    fn abs(self) -> Self {
        libm::fabsf(self)
    }
    fn ln(self) -> Self {
        libm::logf(self)
    }
    fn log2(self) -> Self {
        libm::log2f(self)
    }
    fn log10(self) -> Self {
        libm::log10f(self)
    }
    fn log(self, base: Self) -> Self {
        libm::logf(self) / libm::logf(base)
    }
    fn exp(self) -> Self {
        libm::expf(self)
    }
    fn exp2(self) -> Self {
        libm::exp2f(self)
    }
    fn powf(self, n: Self) -> Self {
        libm::powf(self, n)
    }
    fn powi(self, n: i32) -> Self {
        libm::powf(self, n as Self)
    }
    fn sin(self) -> Self {
        libm::sinf(self)
    }
    fn cos(self) -> Self {
        libm::cosf(self)
    }
    fn tan(self) -> Self {
        libm::tanf(self)
    }
    fn atan2(self, other: Self) -> Self {
        libm::atan2f(self, other)
    }
    fn atan(self) -> Self {
        libm::atanf(self)
    }
    fn asin(self) -> Self {
        libm::asinf(self)
    }
    fn acos(self) -> Self {
        libm::acosf(self)
    }
    fn sinh(self) -> Self {
        libm::sinhf(self)
    }
    fn cosh(self) -> Self {
        libm::coshf(self)
    }
    fn tanh(self) -> Self {
        libm::tanhf(self)
    }
    fn cbrt(self) -> Self {
        libm::cbrtf(self)
    }
    fn hypot(self, other: Self) -> Self {
        libm::hypotf(self, other)
    }
    fn mul_add(self, a: Self, b: Self) -> Self {
        libm::fmaf(self, a, b)
    }
}

#[cfg(all(not(feature = "std"), feature = "libm"))]
impl Math for f64 {
    fn sqrt(self) -> Self {
        libm::sqrt(self)
    }
    fn floor(self) -> Self {
        libm::floor(self)
    }
    fn ceil(self) -> Self {
        libm::ceil(self)
    }
    fn round(self) -> Self {
        libm::round(self)
    }
    fn trunc(self) -> Self {
        libm::trunc(self)
    }
    fn fract(self) -> Self {
        self - libm::trunc(self)
    }
    fn abs(self) -> Self {
        libm::fabs(self)
    }
    fn ln(self) -> Self {
        libm::log(self)
    }
    fn log2(self) -> Self {
        libm::log2(self)
    }
    fn log10(self) -> Self {
        libm::log10(self)
    }
    fn log(self, base: Self) -> Self {
        libm::log(self) / libm::log(base)
    }
    fn exp(self) -> Self {
        libm::exp(self)
    }
    fn exp2(self) -> Self {
        libm::exp2(self)
    }
    fn powf(self, n: Self) -> Self {
        libm::pow(self, n)
    }
    fn powi(self, n: i32) -> Self {
        libm::pow(self, n as Self)
    }
    fn sin(self) -> Self {
        libm::sin(self)
    }
    fn cos(self) -> Self {
        libm::cos(self)
    }
    fn tan(self) -> Self {
        libm::tan(self)
    }
    fn atan2(self, other: Self) -> Self {
        libm::atan2(self, other)
    }
    fn atan(self) -> Self {
        libm::atan(self)
    }
    fn asin(self) -> Self {
        libm::asin(self)
    }
    fn acos(self) -> Self {
        libm::acos(self)
    }
    fn sinh(self) -> Self {
        libm::sinh(self)
    }
    fn cosh(self) -> Self {
        libm::cosh(self)
    }
    fn tanh(self) -> Self {
        libm::tanh(self)
    }
    fn cbrt(self) -> Self {
        libm::cbrt(self)
    }
    fn hypot(self, other: Self) -> Self {
        libm::hypot(self, other)
    }
    fn mul_add(self, a: Self, b: Self) -> Self {
        libm::fma(self, a, b)
    }
}