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//! rbit
/// Bit reverse
pub trait Rbit {
/// Reverse the bit order.
///
/// # Instructions
///
/// - [`RBIT`](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.
/// ddi0487a.k_10775/index.html):
/// - Description: Reverse Bits reverses the bit order in a register.
/// - Architecture: ARMv7, ARMv8.
/// - Registers: 32 (v7) / 64 (v8) bits.
///
/// # Example
///
/// ```
/// # use bitintr::*;
/// assert_eq!(0b0011_0001_u8.rbit(), 0b1000_1100_u8);
/// assert_eq!(0b0000_0000_0100_1011_u16.rbit(), 0b1101_0010_0000_0000_u16);
/// assert_eq!(
/// 0b11111111_u32.rbit(),
/// 0b11111111_00000000_00000000_00000000_u32
/// );
/// ```
fn rbit(self) -> Self;
}
cfg_if! {
// The reverse_bits methods have been stabilized and should land
// in Rust 1.37.0 .
if #[cfg(bitintr_nightly)] {
macro_rules! impl_rbit {
($id:ident) => {
impl Rbit for $id {
#[inline]
fn rbit(self) -> Self {
self.reverse_bits()
}
}
};
}
} else {
macro_rules! impl_rbit {
($id:ident) => {
impl Rbit for $id {
#[inline]
fn rbit(self) -> Self {
if crate::mem::size_of::<Self>() == 1 {
return (((self as u8 as u64).wrapping_mul(0x80200802_u64)
& 0x0884422110_u64)
.wrapping_mul(0x0101010101_u64)
.wrapping_shr(32)) as Self;
}
let mut x = self;
let byte_width = crate::mem::size_of::<Self>() as u32;
let bit_width = byte_width * 8;
let k = bit_width - 1;
{
let mut up0 = |i: u32, l: u64, r: u64| {
if k & i > 0 {
x = (((x as u64 & l).wrapping_shl(i))
| ((x as u64 & r).wrapping_shr(i)))
as Self;
}
};
up0(
1,
0x5555555555555555_u64,
0xAAAAAAAAAAAAAAAA_u64,
);
up0(
2,
0x3333333333333333_u64,
0xCCCCCCCCCCCCCCCC_u64,
);
up0(
4,
0x0F0F0F0F0F0F0F0F_u64,
0xF0F0F0F0F0F0F0F0_u64,
);
}
{
let mut up1 = |i: u32, s: u32, l: u64, r: u64| {
if byte_width > i && (k & s > 0) {
x = (((x as u64 & l).wrapping_shl(s))
| ((x as u64 & r).wrapping_shr(s)))
as Self;
}
};
up1(
1,
8,
0x00FF00FF00FF00FF_u64,
0xFF00FF00FF00FF00_u64,
);
up1(
2,
16,
0x0000FFFF0000FFFF_u64,
0xFFFF0000FFFF0000_u64,
);
up1(
4,
32,
0x00000000FFFFFFFF_u64,
0xFFFFFFFF00000000_u64,
);
}
x
}
}
};
}
}
}
impl_all!(impl_rbit: u8, u16, u32, u64, i8, i16, i32, i64);
#[cfg(test)]
mod tests {
use super::Rbit;
#[test]
fn rbit_u8() {
(0..u8::max_value())
.map(|x| {
assert_eq!(x, x.rbit().rbit());
let x = x as i8;
assert_eq!(x, x.rbit().rbit());
})
.count();
}
#[test]
fn rbit_u16() {
(0..u16::max_value())
.map(|x| {
assert_eq!(x, x.rbit().rbit());
let x = x as i16;
assert_eq!(x, x.rbit().rbit());
})
.count();
}
#[test]
fn rbit_u32() {
(0..u32::max_value())
.take(1000000)
.map(|x| {
assert_eq!(x, x.rbit().rbit());
let x = x as i32;
assert_eq!(x, x.rbit().rbit());
})
.count();
}
#[test]
fn rbit_u64() {
(0..u64::max_value())
.take(1000000)
.map(|x| {
assert_eq!(x, x.rbit().rbit());
let x = x as i64;
assert_eq!(x, x.rbit().rbit());
})
.count();
}
#[test]
fn rbit_tests() {
{
// width: 8
let o_u8 = 0b1101_0011u8;
let r_u8 = 0b1100_1011u8;
assert_eq!(o_u8, 211);
assert_eq!(r_u8, 203);
assert_eq!(o_u8.rbit(), r_u8);
let o_i8 = o_u8 as i8;
let r_i8 = r_u8 as i8;
assert_eq!(o_i8.rbit(), r_i8);
}
{
//width: 16
let o_u16 = 0b1101_0011_1110_1010u16;
let r_u16 = 0b0101_0111_1100_1011u16;
assert_eq!(o_u16.rbit(), r_u16);
assert_eq!((o_u16 as i16).rbit(), r_u16 as i16);
}
{
// width: 32
let o_u32 = 0b1101_0011_1110_1010_1101_0011_1010_1010u32;
let r_u32 = 0b0101_0101_1100_1011_0101_0111_1100_1011u32;
assert_eq!(o_u32.rbit(), r_u32);
assert_eq!((o_u32 as i32).rbit(), r_u32 as i32);
}
{
// width: 64
let o_u64 = 0b1101_0011_0010_1010_1111_0011_1010_1010_1101_0011_1110_1010_1101_0011_1010_1010u64;
let r_u64 = 0b0101_0101_1100_1011_0101_0111_1100_1011_0101_0101_1100_1111_0101_0100_1100_1011u64;
assert_eq!(o_u64.rbit(), r_u64);
assert_eq!((o_u64 as i64).rbit(), r_u64 as i64);
}
}
}