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// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the BastionOS freestanding C++ standard library.
//
// Bit manipulation utilities — all backed by compiler builtins.
//
//===----------------------------------------------------------------------===//
#ifndef _LIBBASTION_BIT_BIT_H
#define _LIBBASTION_BIT_BIT_H
#include <__config>
#include <__type_traits/integral_constant.h>
#include <__type_traits/primary_categories.h>
#include <__type_traits/type_properties.h>
#include <cstdint>
_LIBBASTION_BEGIN_NAMESPACE_STD
// ── endian ──────────────────────────────────────────────────────────────────
enum class endian {
#if defined(__ORDER_LITTLE_ENDIAN__) && defined(__ORDER_BIG_ENDIAN__) && defined(__BYTE_ORDER__)
little = __ORDER_LITTLE_ENDIAN__,
big = __ORDER_BIG_ENDIAN__,
native = __BYTE_ORDER__,
#else
little = 0,
big = 1,
native = 0, // assume little-endian
#endif
};
// ── bit_cast ────────────────────────────────────────────────────────────────
template<class _To, class _From>
_LIBBASTION_NODISCARD constexpr _To bit_cast(const _From& __from) noexcept {
static_assert(sizeof(_To) == sizeof(_From), "bit_cast requires same size types");
static_assert(__is_trivially_copyable(_To), "bit_cast target must be trivially copyable");
static_assert(__is_trivially_copyable(_From), "bit_cast source must be trivially copyable");
return __builtin_bit_cast(_To, __from);
}
// ── Helpers for unsigned integer operations ─────────────────────────────────
namespace __detail {
template<class _Tp>
concept __unsigned_integer = is_unsigned_v<_Tp> && is_integral_v<_Tp> && !__is_same(_Tp, bool);
} // namespace __detail
// ── countl_zero / countl_one ────────────────────────────────────────────────
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr int countl_zero(_Tp __x) noexcept {
if (__x == 0) return static_cast<int>(sizeof(_Tp) * __CHAR_BIT__);
if constexpr (sizeof(_Tp) <= sizeof(unsigned int))
return __builtin_clz(static_cast<unsigned int>(__x)) - (sizeof(unsigned int) - sizeof(_Tp)) * __CHAR_BIT__;
else if constexpr (sizeof(_Tp) <= sizeof(unsigned long))
return __builtin_clzl(static_cast<unsigned long>(__x));
else
return __builtin_clzll(static_cast<unsigned long long>(__x));
}
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr int countl_one(_Tp __x) noexcept {
return countl_zero(static_cast<_Tp>(~__x));
}
// ── countr_zero / countr_one ────────────────────────────────────────────────
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr int countr_zero(_Tp __x) noexcept {
if (__x == 0) return static_cast<int>(sizeof(_Tp) * __CHAR_BIT__);
if constexpr (sizeof(_Tp) <= sizeof(unsigned int))
return __builtin_ctz(static_cast<unsigned int>(__x));
else if constexpr (sizeof(_Tp) <= sizeof(unsigned long))
return __builtin_ctzl(static_cast<unsigned long>(__x));
else
return __builtin_ctzll(static_cast<unsigned long long>(__x));
}
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr int countr_one(_Tp __x) noexcept {
return countr_zero(static_cast<_Tp>(~__x));
}
// ── popcount ────────────────────────────────────────────────────────────────
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr int popcount(_Tp __x) noexcept {
if constexpr (sizeof(_Tp) <= sizeof(unsigned int))
return __builtin_popcount(static_cast<unsigned int>(__x));
else if constexpr (sizeof(_Tp) <= sizeof(unsigned long))
return __builtin_popcountl(static_cast<unsigned long>(__x));
else
return __builtin_popcountll(static_cast<unsigned long long>(__x));
}
// ── has_single_bit ──────────────────────────────────────────────────────────
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr bool has_single_bit(_Tp __x) noexcept {
return __x != 0 && (__x & (__x - 1)) == 0;
}
// ── bit_width ───────────────────────────────────────────────────────────────
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr int bit_width(_Tp __x) noexcept {
return static_cast<int>(sizeof(_Tp) * __CHAR_BIT__) - countl_zero(__x);
}
// ── bit_ceil / bit_floor ────────────────────────────────────────────────────
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr _Tp bit_ceil(_Tp __x) noexcept {
if (__x <= 1) return _Tp(1);
return _Tp(1) << bit_width(static_cast<_Tp>(__x - 1));
}
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr _Tp bit_floor(_Tp __x) noexcept {
if (__x == 0) return 0;
return _Tp(1) << (bit_width(__x) - 1);
}
// ── rotl / rotr ─────────────────────────────────────────────────────────────
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr _Tp rotl(_Tp __x, int __s) noexcept {
constexpr int _Nd = sizeof(_Tp) * __CHAR_BIT__;
int __r = __s % _Nd;
if (__r == 0) return __x;
if (__r < 0) return rotr(__x, -__r);
return static_cast<_Tp>((__x << __r) | (__x >> (_Nd - __r)));
}
template<__detail::__unsigned_integer _Tp>
_LIBBASTION_NODISCARD constexpr _Tp rotr(_Tp __x, int __s) noexcept {
constexpr int _Nd = sizeof(_Tp) * __CHAR_BIT__;
int __r = __s % _Nd;
if (__r == 0) return __x;
if (__r < 0) return rotl(__x, -__r);
return static_cast<_Tp>((__x >> __r) | (__x << (_Nd - __r)));
}
// ── byteswap (C++23) ───────────────────────────────────────────────────────
template<class _Tp>
requires is_integral_v<_Tp>
_LIBBASTION_NODISCARD constexpr _Tp byteswap(_Tp __val) noexcept {
if constexpr (sizeof(_Tp) == 1) {
return __val;
} else if constexpr (sizeof(_Tp) == 2) {
return static_cast<_Tp>(__builtin_bswap16(static_cast<uint16_t>(__val)));
} else if constexpr (sizeof(_Tp) == 4) {
return static_cast<_Tp>(__builtin_bswap32(static_cast<uint32_t>(__val)));
} else if constexpr (sizeof(_Tp) == 8) {
return static_cast<_Tp>(__builtin_bswap64(static_cast<uint64_t>(__val)));
}
}
_LIBBASTION_END_NAMESPACE_STD
#endif // _LIBBASTION_BIT_BIT_H
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