convert between integer and byte array

src/int.rs

@@ -1,3 +1,4 @@
+use core::mem::size_of;
 use core::ops::{BitAnd, BitOr, BitXor, Not, Shl, Shr};
 
 use bounds::Bounded;
@@ -5,6 +6,11 @@ use ops::checked::*;
 use ops::saturating::Saturating;
 use {Num, NumCast};
 
+pub trait Layout {
+    /// The type representation as a byte array.
+    type Bytes;
+}
+
 pub trait PrimInt:
     Sized
     + Copy
@@ -25,6 +31,7 @@ pub trait PrimInt:
     + CheckedMul<Output = Self>
     + CheckedDiv<Output = Self>
     + Saturating
+    + Layout
 {
     /// Returns the number of ones in the binary representation of `self`.
     ///
@@ -278,6 +285,98 @@ pub trait PrimInt:
     /// assert_eq!(2i32.pow(4), 16);
     /// ```
     fn pow(self, exp: u32) -> Self;
+
+    /// Return the memory representation of this integer as a byte array in big-endian byte order.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use num_traits::PrimInt;
+    ///
+    /// let bytes = 0x12345678u32.to_be_bytes();
+    /// assert_eq!(bytes, [0x12, 0x34, 0x56, 0x78]);
+    /// ```
+    fn to_be_bytes(self) -> Self::Bytes;
+
+    /// Return the memory representation of this integer as a byte array in little-endian byte order.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use num_traits::PrimInt;
+    ///
+    /// let bytes = 0x12345678u32.to_le_bytes();
+    /// assert_eq!(bytes, [0x78, 0x56, 0x34, 0x12]);
+    /// ```
+    fn to_le_bytes(self) -> Self::Bytes;
+
+    /// Return the memory representation of this integer as a byte array in native byte order.
+    ///
+    /// As the target platform's native endianness is used,
+    /// portable code should use [`to_be_bytes`] or [`to_le_bytes`], as appropriate, instead.
+    ///
+    /// [`to_be_bytes`]: #method.to_be_bytes
+    /// [`to_le_bytes`]: #method.to_le_bytes
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use num_traits::PrimInt;
+    ///
+    /// let bytes = 0x12345678u32.to_ne_bytes();
+    /// assert_eq!(bytes, if cfg!(target_endian = "big") {
+    ///     [0x12, 0x34, 0x56, 0x78]
+    /// } else {
+    ///     [0x78, 0x56, 0x34, 0x12]
+    /// });
+    /// ```
+    fn to_ne_bytes(self) -> Self::Bytes;
+
+    /// Create an integer value from its representation as a byte array in big endian.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use num_traits::PrimInt;
+    ///
+    /// let value = u32::from_be_bytes([0x12, 0x34, 0x56, 0x78]);
+    /// assert_eq!(value, 0x12345678);
+    /// ```
+    fn from_be_bytes(bytes: Self::Bytes) -> Self;
+
+    /// Create an integer value from its representation as a byte array in little endian.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use num_traits::PrimInt;
+    ///
+    /// let value = u32::from_le_bytes([0x78, 0x56, 0x34, 0x12]);
+    /// assert_eq!(value, 0x12345678);
+    /// ```
+    fn from_le_bytes(bytes: Self::Bytes) -> Self;
+
+    /// Create an integer value from its memory representation as a byte array in native endianness.
+    ///
+    /// As the target platform's native endianness is used,
+    /// portable code likely wants to use [`from_be_bytes`] or [`from_le_bytes`], as appropriate instead.
+    ///
+    /// [`from_be_bytes`]: #method.from_be_bytes
+    /// [`from_le_bytes`]: #method.from_le_bytes
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use num_traits::PrimInt;
+    ///
+    /// let value = u32::from_ne_bytes(if cfg!(target_endian = "big") {
+    ///     [0x12, 0x34, 0x56, 0x78]
+    /// } else {
+    ///     [0x78, 0x56, 0x34, 0x12]
+    /// });
+    /// assert_eq!(value, 0x12345678);
+    /// ```
+    fn from_ne_bytes(bytes: Self::Bytes) -> Self;
 }
 
 macro_rules! prim_int_impl {
@@ -362,6 +461,40 @@ macro_rules! prim_int_impl {
             fn pow(self, exp: u32) -> Self {
                 <$T>::pow(self, exp)
             }
+
+            #[inline]
+            fn to_be_bytes(self) -> Self::Bytes {
+                <$T>::to_be_bytes(self)
+            }
+
+            #[inline]
+            fn to_le_bytes(self) -> Self::Bytes {
+                <$T>::to_le_bytes(self)
+            }
+
+            #[inline]
+            fn to_ne_bytes(self) -> Self::Bytes {
+                <$T>::to_ne_bytes(self)
+            }
+
+            #[inline]
+            fn from_be_bytes(bytes: Self::Bytes) -> Self {
+                <$T>::from_be_bytes(bytes)
+            }
+
+            #[inline]
+            fn from_le_bytes(bytes: Self::Bytes) -> Self {
+                <$T>::from_le_bytes(bytes)
+            }
+
+            #[inline]
+            fn from_ne_bytes(bytes: Self::Bytes) -> Self {
+                <$T>::from_ne_bytes(bytes)
+            }
+        }
+
+        impl Layout for $T {
+            type Bytes = [u8; size_of::<$T>()];
         }
     };
 }

src/lib.rs

@@ -32,7 +32,7 @@ pub use float::FloatConst;
 // pub use real::{FloatCore, Real}; // NOTE: Don't do this, it breaks `use num_traits::*;`.
 pub use cast::{cast, AsPrimitive, FromPrimitive, NumCast, ToPrimitive};
 pub use identities::{one, zero, One, Zero};
-pub use int::PrimInt;
+pub use int::{Layout, PrimInt};
 pub use ops::checked::{
     CheckedAdd, CheckedDiv, CheckedMul, CheckedNeg, CheckedRem, CheckedShl, CheckedShr, CheckedSub,
 };
@@ -90,13 +90,12 @@ pub trait NumOps<Rhs = Self, Output = Self>:
 {
 }
 
-impl<T, Rhs, Output> NumOps<Rhs, Output> for T
-where
+impl<T, Rhs, Output> NumOps<Rhs, Output> for T where
     T: Add<Rhs, Output = Output>
         + Sub<Rhs, Output = Output>
         + Mul<Rhs, Output = Output>
         + Div<Rhs, Output = Output>
-        + Rem<Rhs, Output = Output>,
+        + Rem<Rhs, Output = Output>
 {
 }
 
@@ -105,22 +104,14 @@ where
 ///
 /// This is automatically implemented for types which implement the operators.
 pub trait NumRef: Num + for<'r> NumOps<&'r Self> {}
-impl<T> NumRef for T
-where
-    T: Num + for<'r> NumOps<&'r T>,
-{
-}
+impl<T> NumRef for T where T: Num + for<'r> NumOps<&'r T> {}
 
 /// The trait for references which implement numeric operations, taking the
 /// second operand either by value or by reference.
 ///
 /// This is automatically implemented for types which implement the operators.
 pub trait RefNum<Base>: NumOps<Base, Base> + for<'r> NumOps<&'r Base, Base> {}
-impl<T, Base> RefNum<Base> for T
-where
-    T: NumOps<Base, Base> + for<'r> NumOps<&'r Base, Base>,
-{
-}
+impl<T, Base> RefNum<Base> for T where T: NumOps<Base, Base> + for<'r> NumOps<&'r Base, Base> {}
 
 /// The trait for types implementing numeric assignment operators (like `+=`).
 ///
@@ -130,9 +121,8 @@ pub trait NumAssignOps<Rhs = Self>:
 {
 }
 
-impl<T, Rhs> NumAssignOps<Rhs> for T
-where
-    T: AddAssign<Rhs> + SubAssign<Rhs> + MulAssign<Rhs> + DivAssign<Rhs> + RemAssign<Rhs>,
+impl<T, Rhs> NumAssignOps<Rhs> for T where
+    T: AddAssign<Rhs> + SubAssign<Rhs> + MulAssign<Rhs> + DivAssign<Rhs> + RemAssign<Rhs>
 {
 }
 
@@ -140,22 +130,14 @@ where
 ///
 /// This is automatically implemented for types which implement the operators.
 pub trait NumAssign: Num + NumAssignOps {}
-impl<T> NumAssign for T
-where
-    T: Num + NumAssignOps,
-{
-}
+impl<T> NumAssign for T where T: Num + NumAssignOps {}
 
 /// The trait for `NumAssign` types which also implement assignment operations
 /// taking the second operand by reference.
 ///
 /// This is automatically implemented for types which implement the operators.
 pub trait NumAssignRef: NumAssign + for<'r> NumAssignOps<&'r Self> {}
-impl<T> NumAssignRef for T
-where
-    T: NumAssign + for<'r> NumAssignOps<&'r T>,
-{
-}
+impl<T> NumAssignRef for T where T: NumAssign + for<'r> NumAssignOps<&'r T> {}
 
 macro_rules! int_trait_impl {
     ($name:ident for $($t:ty)*) => ($(