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#pragma once
#include <cassert>
#include <concepts>
#include <cstddef>
#include <cstdint>
#include <type_traits>
#include <base/defines.h>
/** For zero argument, result is zero.
* For arguments with most significand bit set, result is n.
* For other arguments, returns value, rounded up to power of two.
*/
inline size_t roundUpToPowerOfTwoOrZero(size_t n)
{
// if MSB is set, return n, to avoid return zero
if (unlikely(n >= 0x8000000000000000ULL))
return n;
--n;
n |= n >> 1;
n |= n >> 2;
n |= n >> 4;
n |= n >> 8;
n |= n >> 16;
n |= n >> 32;
++n;
return n;
}
template <typename T>
inline uint32_t getLeadingZeroBitsUnsafe(T x)
{
assert(x != 0);
if constexpr (sizeof(T) <= sizeof(unsigned int))
{
return __builtin_clz(x);
}
else if constexpr (sizeof(T) <= sizeof(unsigned long int)) /// NOLINT
{
return __builtin_clzl(x);
}
else
{
return __builtin_clzll(x);
}
}
template <typename T>
inline size_t getLeadingZeroBits(T x)
{
if (!x)
return sizeof(x) * 8;
return getLeadingZeroBitsUnsafe(x);
}
/** Returns log2 of number, rounded down.
* Compiles to single 'bsr' instruction on x86.
* For zero argument, result is unspecified.
*/
template <typename T>
inline uint32_t bitScanReverse(T x)
{
return (std::max<size_t>(sizeof(T), sizeof(unsigned int))) * 8 - 1 - getLeadingZeroBitsUnsafe(x);
}
// Unsafe since __builtin_ctz()-family explicitly state that result is undefined on x == 0
template <typename T>
inline size_t getTrailingZeroBitsUnsafe(T x)
{
assert(x != 0);
if constexpr (sizeof(T) <= sizeof(unsigned int))
{
return __builtin_ctz(x);
}
else if constexpr (sizeof(T) <= sizeof(unsigned long int)) /// NOLINT
{
return __builtin_ctzl(x);
}
else
{
return __builtin_ctzll(x);
}
}
template <typename T>
inline size_t getTrailingZeroBits(T x)
{
if (!x)
return sizeof(x) * 8;
return getTrailingZeroBitsUnsafe(x);
}
/** Returns a mask that has '1' for `bits` LSB set:
* maskLowBits<UInt8>(3) => 00000111
* maskLowBits<Int8>(3) => 00000111
*/
template <typename T>
inline T maskLowBits(unsigned char bits)
{
using UnsignedT = std::make_unsigned_t<T>;
if (bits == 0)
{
return 0;
}
UnsignedT result = static_cast<UnsignedT>(~UnsignedT{0});
if (bits < sizeof(T) * 8)
{
result = static_cast<UnsignedT>(result >> (sizeof(UnsignedT) * 8 - bits));
}
return static_cast<T>(result);
}
template <std::integral T>
constexpr bool isPowerOf2(T number)
{
return number > 0 && (number & (number - 1)) == 0;
}
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