mirror of
https://github.com/LadybirdBrowser/ladybird.git
synced 2024-11-10 13:00:29 +03:00
72 lines
1.4 KiB
C++
72 lines
1.4 KiB
C++
/*
|
|
* Copyright (c) 2022, Leon Albrecht <leon2002.la@gmail.com>
|
|
*
|
|
* SPDX-License-Identifier: BSD-2-Clause
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
#include <AK/BuiltinWrappers.h>
|
|
#include <AK/Concepts.h>
|
|
#include <AK/Types.h>
|
|
|
|
namespace AK {
|
|
|
|
template<Integral T>
|
|
constexpr T exp2(T exponent)
|
|
{
|
|
return 1u << exponent;
|
|
}
|
|
|
|
template<Integral T>
|
|
constexpr T log2(T x)
|
|
{
|
|
return x ? (8 * sizeof(T) - 1) - count_leading_zeroes(static_cast<MakeUnsigned<T>>(x)) : 0;
|
|
}
|
|
|
|
template<Integral T>
|
|
constexpr T ceil_log2(T x)
|
|
{
|
|
if (!x)
|
|
return 0;
|
|
|
|
T log = AK::log2(x);
|
|
log += (x & ((((T)1) << (log - 1)) - 1)) != 0;
|
|
return log;
|
|
}
|
|
|
|
template<Integral I>
|
|
constexpr I pow(I base, I exponent)
|
|
{
|
|
// https://en.wikipedia.org/wiki/Exponentiation_by_squaring
|
|
if (exponent < 0)
|
|
return 0;
|
|
if (exponent == 0)
|
|
return 1;
|
|
|
|
I res = 1;
|
|
while (exponent > 0) {
|
|
if (exponent & 1)
|
|
res *= base;
|
|
base *= base;
|
|
exponent /= 2u;
|
|
}
|
|
return res;
|
|
}
|
|
|
|
template<auto base, Unsigned U = decltype(base)>
|
|
constexpr bool is_power_of(U x)
|
|
{
|
|
if constexpr (base == 2)
|
|
return is_power_of_two(x);
|
|
|
|
// FIXME: I am naive! A log2-based approach (pow<U>(base, (log2(x) / log2(base))) == x) does not work due to rounding errors.
|
|
for (U exponent = 0; exponent <= log2(x) / log2(base) + 1; ++exponent) {
|
|
if (pow<U>(base, exponent) == x)
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
}
|