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120 lines
2.3 KiB
C++
120 lines
2.3 KiB
C++
#pragma once
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#include <cstddef>
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#include <cstdint>
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#include <cassert>
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#include <type_traits>
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#include <common/defines.h>
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/** For zero argument, result is zero.
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* For arguments with most significand bit set, result is n.
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* For other arguments, returns value, rounded up to power of two.
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*/
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inline size_t roundUpToPowerOfTwoOrZero(size_t n)
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{
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// if MSB is set, return n, to avoid return zero
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if (unlikely(n >= 0x8000000000000000ULL))
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return n;
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--n;
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n |= n >> 1;
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n |= n >> 2;
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n |= n >> 4;
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n |= n >> 8;
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n |= n >> 16;
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n |= n >> 32;
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++n;
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return n;
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}
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template <typename T>
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inline size_t getLeadingZeroBitsUnsafe(T x)
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{
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assert(x != 0);
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if constexpr (sizeof(T) <= sizeof(unsigned int))
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{
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return __builtin_clz(x);
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}
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else if constexpr (sizeof(T) <= sizeof(unsigned long int))
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{
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return __builtin_clzl(x);
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}
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else
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{
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return __builtin_clzll(x);
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}
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}
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template <typename T>
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inline size_t getLeadingZeroBits(T x)
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{
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if (!x)
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return sizeof(x) * 8;
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return getLeadingZeroBitsUnsafe(x);
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}
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/** Returns log2 of number, rounded down.
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* Compiles to single 'bsr' instruction on x86.
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* For zero argument, result is unspecified.
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*/
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template <typename T>
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inline uint32_t bitScanReverse(T x)
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{
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return (std::max<size_t>(sizeof(T), sizeof(unsigned int))) * 8 - 1 - getLeadingZeroBitsUnsafe(x);
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}
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// Unsafe since __builtin_ctz()-family explicitly state that result is undefined on x == 0
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template <typename T>
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inline size_t getTrailingZeroBitsUnsafe(T x)
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{
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assert(x != 0);
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if constexpr (sizeof(T) <= sizeof(unsigned int))
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{
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return __builtin_ctz(x);
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}
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else if constexpr (sizeof(T) <= sizeof(unsigned long int))
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{
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return __builtin_ctzl(x);
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}
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else
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{
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return __builtin_ctzll(x);
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}
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}
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template <typename T>
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inline size_t getTrailingZeroBits(T x)
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{
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if (!x)
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return sizeof(x) * 8;
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return getTrailingZeroBitsUnsafe(x);
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}
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/** Returns a mask that has '1' for `bits` LSB set:
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* maskLowBits<UInt8>(3) => 00000111
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*/
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template <typename T>
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inline T maskLowBits(unsigned char bits)
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{
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if (bits == 0)
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{
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return 0;
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}
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T result = static_cast<T>(~T{0});
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if (bits < sizeof(T) * 8)
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{
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result = static_cast<T>(result >> (sizeof(T) * 8 - bits));
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}
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return result;
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}
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