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//! bextr
/// Bit field extract
pub trait Bextr {
/// Bit field extract.
///
/// Extracts bits in range `[start, start + length)` from the `source` to
/// the least significant bits of the result.
///
/// Bits `[7,0]` of `range` specify the index to the first bit in the
/// range to be extracted, and bits `[15,8]` specify the length of the
/// range.
///
/// Only bits up to `size_of::<T>()*8 - 1` are extracted.
///
/// The extracted bits are written in the result starting from the
/// least-significant bit. The high-order bits of the result are zeroed.
///
/// # Instructions
///
/// - [`BEXTR`](http://www.felixcloutier.com/x86/BEXTR.html):
/// - Description: Bit field extract.
/// - Architecture: x86.
/// - Instruction set: BMI.
/// - Registers: 32/64 bit.
///
/// # Example
///
/// ```
/// # use bitintr::*;
/// assert_eq!(0b0101_0000u8.bextr(4, 4), 0b0000_0101u8);
/// ```
fn bextr(self, start: Self, length: Self) -> Self;
/// Bit Field Extract (with immediate operand).
///
/// Extracts bits in `range` from the `source` to the least significant
/// bits of the result. Bits `[7,0]` of `range` specify the index to
/// the first bit in the range to be extracted, and bits `[15,8]`
/// specify the length of the range.
///
/// Only bits up to `size_of::<T>()*8 - 1` are extracted.
///
/// The extracted bits are written in the result starting from the
/// least-significant bit. The high-order bits of the result are zeroed.
///
/// # Instructions
///
/// - [`BEXTR`](https://support.amd.com/TechDocs/24594.pdf):
/// - Description: Bit field extract (with immediate).
/// - Architecture: x86.
/// - Instruction set: TBM.
/// - Registers: 32/64 bit.
///
/// # Example
///
/// ```
/// # use bitintr::*;
/// assert_eq!(
/// 0b0000_0000_0101_0000_u16.bextri(0b0100_0000_0100_u32),
/// 0b0000_0000_0000_0101_u16
/// );
/// ```
fn bextri(self, range: u32) -> Self;
}
macro_rules! bextr_impl {
($ty:ty) => {
#[inline]
fn bextr_(value: $ty, start: $ty, length: $ty) -> $ty {
(value >> start) & ((1 << length) - 1)
}
};
($ty:ty, $intr:ident) => {
cfg_if! {
if #[cfg(all(
any(target_arch = "x86", target_arch = "x86_64"),
target_feature = "bmi2"
))] {
#[inline]
#[target_feature(enable = "bmi2")]
unsafe fn bextr_(value: $ty, start: $ty, length: $ty) -> $ty {
crate::arch::$intr(
value as _,
start as u32,
length as u32,
) as _
}
} else {
bextr_impl!($ty);
}
}
};
}
macro_rules! impl_bextr {
($id:ident $(,$args:ident)*) => {
impl Bextr for $id {
#[inline]
#[allow(unused_unsafe)]
fn bextr(self, start: Self, length: Self) -> Self {
bextr_impl!($id $(,$args)*);
// UNSAFETY: this is always safe, because
// the unsafe `#[target_feature]` function
// is only generated when the feature is
// statically-enabled at compile-time.
unsafe { bextr_(self, start, length) }
}
#[inline]
fn bextri(self, range: u32) -> Self {
self.bextr((range & 0xff) as Self, (range >> 8) as Self)
}
}
};
}
impl_all!(impl_bextr: u8, u16, i8, i16);
cfg_if! {
if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
impl_bextr!(u32, _bextr_u32);
impl_bextr!(i32, _bextr_u32);
cfg_if! {
if #[cfg(target_arch = "x86_64")] {
impl_bextr!(u64, _bextr_u64);
impl_bextr!(i64, _bextr_u64);
} else {
impl_all!(impl_bextr: i64, u64);
}
}
} else {
impl_all!(impl_bextr: u32, i32, i64, u64);
}
}