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//! A crate that provides support for half-precision 16-bit floating point types.
//!
//! This crate provides the [`f16`] type, which is an implementation of the IEEE 754-2008 standard
//! [`binary16`] a.k.a `half` floating point type. This 16-bit floating point type is intended for
//! efficient storage where the full range and precision of a larger floating point value is not
//! required. This is especially useful for image storage formats.
//!
//! This crate also provides a [`bf16`] type, an alternative 16-bit floating point format. The
//! [`bfloat16`] format is a truncated IEEE 754 standard `binary32` float that preserves the
//! exponent to allow the same range as [`f32`] but with only 8 bits of precision (instead of 11
//! bits for [`f16`]). See the [`bf16`] type for details.
//!
//! Because [`f16`] and [`bf16`] are primarily for efficient storage, floating point operations such
//! as addition, multiplication, etc. are not implemented by hardware. While this crate does provide
//! the appropriate trait implementations for basic operations, they each convert the value to
//! [`f32`] before performing the operation and then back afterward. When performing complex
//! arithmetic, manually convert to and from [`f32`] before and after to reduce repeated conversions
//! for each operation.
//!
//! This crate also provides a [`slice`][mod@slice] module for zero-copy in-place conversions of
//! [`u16`] slices to both [`f16`] and [`bf16`], as well as efficient vectorized conversions of
//! larger buffers of floating point values to and from these half formats.
//!
//! The crate uses `#[no_std]` by default, so can be used in embedded environments without using the
//! Rust [`std`] library. A `std` feature to enable support for the standard library is available,
//! see the [Cargo Features](#cargo-features) section below.
//!
//! A [`prelude`] module is provided for easy importing of available utility traits.
//!
//! # Cargo Features
//!
//! This crate supports a number of optional cargo features. None of these features are enabled by
//! default, even `std`.
//!
//! - **`use-intrinsics`** -- Use [`core::arch`] hardware intrinsics for `f16` and `bf16` conversions
//! if available on the compiler target. This feature currently only works on nightly Rust
//! until the corresponding intrinsics are stabilized.
//!
//! When this feature is enabled and the hardware supports it, the functions and traits in the
//! [`slice`][mod@slice] module will use vectorized SIMD intructions for increased efficiency.
//!
//! By default, without this feature, conversions are done only in software, which will also be
//! the fallback if the target does not have hardware support. Note that without the `std`
//! feature enabled, no runtime CPU feature detection is used, so the hardware support is only
//! compiled if the compiler target supports the CPU feature.
//!
//! - **`alloc`** -- Enable use of the [`alloc`] crate when not using the `std` library.
//!
//! Among other functions, this enables the [`vec`] module, which contains zero-copy
//! conversions for the [`Vec`] type. This allows fast conversion between raw `Vec<u16>` bits and
//! `Vec<f16>` or `Vec<bf16>` arrays, and vice versa.
//!
//! - **`std`** -- Enable features that depend on the Rust [`std`] library. This also enables the
//! `alloc` feature automatically.
//!
//! Enabling the `std` feature also enables runtime CPU feature detection when the
//! `use-intrsincis` feature is also enabled. Without this feature detection, intrinsics are only
//! used when compiler target supports the target feature.
//!
//! - **`serde`** -- Adds support for the [`serde`] crate by implementing [`Serialize`] and
//! [`Deserialize`] traits for both [`f16`] and [`bf16`].
//!
//! - **`num-traits`** -- Adds support for the [`num-traits`] crate by implementing [`ToPrimitive`],
//! [`FromPrimitive`], [`AsPrimitive`], [`Num`], [`Float`], [`FloatCore`], and [`Bounded`] traits
//! for both [`f16`] and [`bf16`].
//!
//! - **`bytemuck`** -- Adds support for the [`bytemuck`] crate by implementing [`Zeroable`] and
//! [`Pod`] traits for both [`f16`] and [`bf16`].
//!
//! - **`zerocopy`** -- Adds support for the [`zerocopy`] crate by implementing [`AsBytes`] and
//! [`FromBytes`] traits for both [`f16`] and [`bf16`].
//!
#![cfg_attr(
feature = "alloc",
doc = "
[`vec`]: mod@vec"
)]
#![cfg_attr(
not(feature = "alloc"),
doc = "
[`vec`]: #
)]
#![cfg_attr(
feature = "serde",
doc = "
[`Serialize`]: serde::Serialize
[`Deserialize`]: serde::Deserialize"
)]
#![cfg_attr(
not(feature = "serde"),
doc = "
)]
#![cfg_attr(
feature = "num-traits",
doc = "
[`ToPrimitive`]: ::num_traits::ToPrimitive
[`FromPrimitive`]: ::num_traits::FromPrimitive
[`AsPrimitive`]: ::num_traits::AsPrimitive
[`Num`]: ::num_traits::Num
[`Float`]: ::num_traits::Float
[`FloatCore`]: ::num_traits::float::FloatCore
[`Bounded`]: ::num_traits::Bounded"
)]
#![cfg_attr(
not(feature = "num-traits"),
doc = "
)]
#![cfg_attr(
feature = "bytemuck",
doc = "
[`Zeroable`]: bytemuck::Zeroable
[`Pod`]: bytemuck::Pod"
)]
#![cfg_attr(
not(feature = "bytemuck"),
doc = "
)]
#![cfg_attr(
feature = "zerocopy",
doc = "
[`AsBytes`]: zerocopy::AsBytes
[`FromBytes`]: zerocopy::FromBytes"
)]
#![cfg_attr(
not(feature = "zerocopy"),
doc = "
)]
#![warn(
missing_docs,
missing_copy_implementations,
missing_debug_implementations,
trivial_numeric_casts,
future_incompatible
)]
#![allow(clippy::verbose_bit_mask, clippy::cast_lossless)]
#![cfg_attr(not(feature = "std"), no_std)]
#![cfg_attr(
all(
feature = "use-intrinsics",
any(target_arch = "x86", target_arch = "x86_64")
),
feature(stdsimd, f16c_target_feature)
)]
#![doc(test(attr(deny(warnings), allow(unused))))]
#![cfg_attr(docsrs, feature(doc_cfg))]
#[cfg(feature = "alloc")]
extern crate alloc;
mod bfloat;
mod binary16;
#[cfg(feature = "num-traits")]
mod num_traits;
pub mod slice;
#[cfg(feature = "alloc")]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
pub mod vec;
pub use bfloat::bf16;
#[doc(hidden)]
#[allow(deprecated)]
pub use binary16::consts;
pub use binary16::f16;
/// A collection of the most used items and traits in this crate for easy importing.
///
/// # Examples
///
/// ```rust
/// use half::prelude::*;
/// ```
pub mod prelude {
#[doc(no_inline)]
pub use crate::{
bf16, f16,
slice::{HalfBitsSliceExt, HalfFloatSliceExt},
};
#[cfg(feature = "alloc")]
#[doc(no_inline)]
#[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
pub use crate::vec::{HalfBitsVecExt, HalfFloatVecExt};
}
// Keep this module private to crate
mod private {
use crate::{bf16, f16};
pub trait SealedHalf {}
impl SealedHalf for f16 {}
impl SealedHalf for bf16 {}
}