100 lines
2.2 KiB
C++
100 lines
2.2 KiB
C++
#pragma once
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#include <cassert>
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#ifdef _MSC_VER
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# include <intrin.h>
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#endif
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#ifdef __GNUG__
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# include <x86intrin.h>
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#endif
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#if !(defined(_MSC_VER) || defined(__GNUG__))
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# include <bitset>
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#endif
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namespace EightBit {
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[[nodiscard]] int countBits(uint8_t value) noexcept;
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[[nodiscard]] bool oddParity(uint8_t value) noexcept;
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[[nodiscard]] int findFirstSet(unsigned long value) noexcept;
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}
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inline int EightBit::countBits(uint8_t value) noexcept {
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#if defined(_MSC_VER)
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return __popcnt(value);
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#elif defined(__GNUG__)
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return __builtin_popcount(value);
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#else
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/*
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Published in 1988, the C Programming Language 2nd Ed.
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(by Brian W.Kernighan and Dennis M.Ritchie) mentions
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this in exercise 2 - 9. On April 19, 2006 Don Knuth pointed
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out to me that this method "was first published by Peter
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Wegner in CACM 3 (1960), 322.
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(Also discovered independently by Derrick Lehmer and published
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in 1964 in a book edited by Beckenbach.)"
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*/
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int count; // c accumulates the total bits set in value
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for (count = 0; value; ++count)
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value &= value - 1; // clear the least significant bit set
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return count;
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#endif
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}
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inline bool EightBit::oddParity(const uint8_t value) noexcept {
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#ifdef __GNUG__
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return __builtin_parity(value);
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#else
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return countBits(value) % 2;
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#endif
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}
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inline int EightBit::findFirstSet(const unsigned long value) noexcept {
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#if defined(_MSC_VER)
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unsigned long index = 0;
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if (_BitScanForward(&index, value))
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return index + 1;
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return 0;
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#elif defined(__GNUG__)
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return __builtin_ffs(value);
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#else
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std::bitset<sizeof(unsigned long) * 8> bits(value);
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for (size_t i = bits.size() - 1; i >= 0; --i)
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if (bits.test(i))
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return i + 1;
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return 0;
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#endif
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}
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#define PARITY(x) EightBit::oddParity(x)
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#ifdef _MSC_VER
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# define ASSUME(x) __assume(x);
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# define LIKELY(x) (x)
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# define UNLIKELY(x) (x)
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# define UNREACHABLE { ASSUME(0); assert(false && "unreachable"); }
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#elif defined(__GNUG__)
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# define ASSUME(x) { if (!x) __builtin_unreachable(); }
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# define LIKELY(x) __builtin_expect(!!(x), 1)
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# define UNLIKELY(x) __builtin_expect(!!(x), 0)
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# define UNREACHABLE __builtin_unreachable();
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#else
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# define ASSUME(x) assert(x);
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# define LIKELY(x) (x)
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# define UNLIKELY(x) (x)
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# define UNREACHABLE ASSUME(0)
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#endif
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