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//! Types for compile-time and run-time endianity.
use core::convert::TryInto;
use core::fmt::Debug;
/// A trait describing the endianity of some buffer.
pub trait Endianity: Debug + Default + Clone + Copy + PartialEq + Eq {
/// Return true for big endian byte order.
fn is_big_endian(self) -> bool;
/// Return true for little endian byte order.
#[inline]
fn is_little_endian(self) -> bool {
!self.is_big_endian()
}
/// Reads an unsigned 16 bit integer from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 2`.
#[inline]
fn read_u16(self, buf: &[u8]) -> u16 {
let bytes: &[u8; 2] = buf[..2].try_into().unwrap();
if self.is_big_endian() {
u16::from_be_bytes(*bytes)
} else {
u16::from_le_bytes(*bytes)
}
}
/// Reads an unsigned 32 bit integer from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 4`.
#[inline]
fn read_u32(self, buf: &[u8]) -> u32 {
let bytes: &[u8; 4] = buf[..4].try_into().unwrap();
if self.is_big_endian() {
u32::from_be_bytes(*bytes)
} else {
u32::from_le_bytes(*bytes)
}
}
/// Reads an unsigned 64 bit integer from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 8`.
#[inline]
fn read_u64(self, buf: &[u8]) -> u64 {
let bytes: &[u8; 8] = buf[..8].try_into().unwrap();
if self.is_big_endian() {
u64::from_be_bytes(*bytes)
} else {
u64::from_le_bytes(*bytes)
}
}
/// Read an unsigned n-bytes integer u64.
///
/// # Panics
///
/// Panics when `buf.len() < 1` or `buf.len() > 8`.
#[inline]
fn read_uint(&mut self, buf: &[u8]) -> u64 {
let mut tmp = [0; 8];
if self.is_big_endian() {
tmp[8 - buf.len()..].copy_from_slice(buf);
} else {
tmp[..buf.len()].copy_from_slice(buf);
}
self.read_u64(&tmp)
}
/// Reads a signed 16 bit integer from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 2`.
#[inline]
fn read_i16(self, buf: &[u8]) -> i16 {
self.read_u16(buf) as i16
}
/// Reads a signed 32 bit integer from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 4`.
#[inline]
fn read_i32(self, buf: &[u8]) -> i32 {
self.read_u32(buf) as i32
}
/// Reads a signed 64 bit integer from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 8`.
#[inline]
fn read_i64(self, buf: &[u8]) -> i64 {
self.read_u64(buf) as i64
}
/// Reads a 32 bit floating point number from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 8`.
#[inline]
fn read_f32(self, buf: &[u8]) -> f32 {
f32::from_bits(self.read_u32(buf))
}
/// Reads a 32 bit floating point number from `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 8`.
#[inline]
fn read_f64(self, buf: &[u8]) -> f64 {
f64::from_bits(self.read_u64(buf))
}
/// Writes an unsigned 16 bit integer `n` to `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 2`.
#[inline]
fn write_u16(self, buf: &mut [u8], n: u16) {
let bytes = if self.is_big_endian() {
n.to_be_bytes()
} else {
n.to_le_bytes()
};
buf[..2].copy_from_slice(&bytes);
}
/// Writes an unsigned 32 bit integer `n` to `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 4`.
#[inline]
fn write_u32(self, buf: &mut [u8], n: u32) {
let bytes = if self.is_big_endian() {
n.to_be_bytes()
} else {
n.to_le_bytes()
};
buf[..4].copy_from_slice(&bytes);
}
/// Writes an unsigned 64 bit integer `n` to `buf`.
///
/// # Panics
///
/// Panics when `buf.len() < 8`.
#[inline]
fn write_u64(self, buf: &mut [u8], n: u64) {
let bytes = if self.is_big_endian() {
n.to_be_bytes()
} else {
n.to_le_bytes()
};
buf[..8].copy_from_slice(&bytes);
}
}
/// Byte order that is selectable at runtime.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum RunTimeEndian {
/// Little endian byte order.
Little,
/// Big endian byte order.
Big,
}
impl Default for RunTimeEndian {
#[cfg(target_endian = "little")]
#[inline]
fn default() -> RunTimeEndian {
RunTimeEndian::Little
}
#[cfg(target_endian = "big")]
#[inline]
fn default() -> RunTimeEndian {
RunTimeEndian::Big
}
}
impl Endianity for RunTimeEndian {
#[inline]
fn is_big_endian(self) -> bool {
self != RunTimeEndian::Little
}
}
/// Little endian byte order.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct LittleEndian;
impl Default for LittleEndian {
#[inline]
fn default() -> LittleEndian {
LittleEndian
}
}
impl Endianity for LittleEndian {
#[inline]
fn is_big_endian(self) -> bool {
false
}
}
/// Big endian byte order.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct BigEndian;
impl Default for BigEndian {
#[inline]
fn default() -> BigEndian {
BigEndian
}
}
impl Endianity for BigEndian {
#[inline]
fn is_big_endian(self) -> bool {
true
}
}
/// The native endianity for the target platform.
#[cfg(target_endian = "little")]
pub type NativeEndian = LittleEndian;
#[cfg(target_endian = "little")]
#[allow(non_upper_case_globals)]
#[doc(hidden)]
pub const NativeEndian: LittleEndian = LittleEndian;
/// The native endianity for the target platform.
#[cfg(target_endian = "big")]
pub type NativeEndian = BigEndian;
#[cfg(target_endian = "big")]
#[allow(non_upper_case_globals)]
#[doc(hidden)]
pub const NativeEndian: BigEndian = BigEndian;