<xstd/ints/bit/byteswap.hpp>

xstd::byteswap

template<class T>
  constexpr auto byteswap(T x) noexcept(see below) -> T;

Reverses the bytes of an integer's value, for every integer whose width is a whole number of bytes.

Parameters

Parameter	Meaning
x	the value whose bytes are reversed

Constraints: Either std::byteswap(x) is well-formed, T is integral and no wider, sign bit included, than the widest unsigned type xstd hands to the standard library (uint128 where XSTD_HAS_INT128 is defined, and unsigned long long otherwise), and has_unique_object_representations_v<T> is true; or T models integer and numeric_limits<make_unsigned_t<T>>::digits is a multiple of numeric_limits<unsigned char>::digits. So bit_int<24> and bit_uint<24> are taken and bit_int<13> and bit_uint<13> are not, and bool and char8_t are taken exactly where std::byteswap takes them.

Return value

• Returns: std::byteswap(x) where the first branch of the constraint holds.
• Returns: Otherwise static_cast<T>(u), where u is the value of static_cast<make_unsigned_t<T>>(x) with its bytes in reverse order: the byte n places from the least significant end lands n places from the most significant end.

Exceptions

The exception specification is true for the forwarding overload, and otherwise nothrow_const_operators<T> and nothrow_const_operators<make_unsigned_t<T>>.

Remarks

[bit.byteswap] reverses the object representation and mandates that T have no padding bits. The template reverses the value representation, so it takes a type with padding bits that the standard function's Mandates element rejects, and the constraint keeps every such type away from std::byteswap, including the _BitInt widths libc++ calls integral and then refuses to swap.

Notes

• Swapping twice is the identity.
• A signed T is swapped through its unsigned counterpart, as std::byteswap swaps a signed type.
• A width of whole bytes that fills no whole object, such as bit_uint<24>, is swapped as its value, three bytes where the object has four.
• A call is a constant expression.

See also

Entity	Relation
bit_reverse	reverses the bits rather than the bytes
bit_int, bit_uint	the bit-precise types, swapped as their value
std::byteswap	the standard function it forwards to