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113 lines
2.6 KiB
C++
113 lines
2.6 KiB
C++
#pragma once
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#if __cplusplus >= 202002L || (defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
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#include <bit>
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namespace json::_bitops
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{
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using std::countl_one;
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using std::countl_zero;
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using std::countr_one;
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using std::countr_zero;
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inline constexpr bool is_little_endian()
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{
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return std::endian::native == std::endian::little;
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}
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}
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#else
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#include <cstdint>
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namespace json::_bitops
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{
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#if defined(__GNUC__) || defined(__clang__)
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inline constexpr int countl_zero(uint32_t x)
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{
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if constexpr (sizeof(uint32_t) == sizeof(unsigned int)) return x == 0 ? 32 : __builtin_clz(x);
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if constexpr (sizeof(uint32_t) == sizeof(unsigned long)) return x == 0 ? 32 : __builtin_clzl(x);
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return x == 0 ? 32 : __builtin_clzll(x);
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}
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inline constexpr int countr_zero(uint32_t x)
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{
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if constexpr (sizeof(uint32_t) == sizeof(unsigned int)) return x == 0 ? 32 : __builtin_ctz(x);
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if constexpr (sizeof(uint32_t) == sizeof(unsigned long)) return x == 0 ? 32 : __builtin_ctzl(x);
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return x == 0 ? 32 : __builtin_ctzll(x);
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}
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inline constexpr int countl_zero(uint64_t x)
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{
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return x == 0 ? 64 : __builtin_clzll(x);
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}
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inline constexpr int countr_zero(uint64_t x)
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{
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return x == 0 ? 64 : __builtin_ctzll(x);
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}
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#elif defined(_MSC_VER)
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#ifdef __AVX2__
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// lzcnt intrinsics is not constexpr
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inline int countl_zero(uint32_t x)
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{
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return __lzcnt(x);
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}
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inline int countr_zero(uint32_t x)
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{
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return _tzcnt_u32(x);
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}
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inline int countl_zero(uint64_t x)
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{
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return (int)__lzcnt64(x);
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}
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inline int countr_zero(uint64_t x)
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{
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return (int)_tzcnt_u64(x);
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}
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#else
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inline constexpr int countl_zero(uint32_t x)
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{
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unsigned long index = 0;
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return _BitScanReverse(&index, x) ? 31 - index : 32;
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}
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inline constexpr int countr_zero(uint32_t x)
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{
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unsigned long index = 0;
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return _BitScanForward(&index, x) ? index : 32;
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}
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inline constexpr int countl_zero(uint64_t x)
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{
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unsigned long index = 0;
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return _BitScanReverse64(&index, x) ? 63 - index : 64;
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}
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inline constexpr int countr_zero(uint64_t x)
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{
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unsigned long index = 0;
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return _BitScanForward64(&index, x) ? index : 64;
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}
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#endif // __AVX2__
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#else // compiler
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#error "bring your own bit counting implementation"
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#endif
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inline int countl_one(uint32_t x)
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{
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return countl_zero(~x);
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}
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inline int countr_one(uint32_t x)
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{
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return countr_zero(~x);
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}
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inline int countl_one(uint64_t x)
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{
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return countl_zero(~x);
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}
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inline int countr_one(uint64_t x)
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{
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return countr_zero(~x);
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}
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// no constexpr endian awareness before C++20
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inline bool is_little_endian()
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{
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union {
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uint32_t u32;
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uint8_t u8;
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} u = { 0x01020304 };
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return u.u8 == 4;
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}
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} // namespace json::_bitops
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#endif // C++20
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