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#pragma once
#include "../Common.h"
#include <cstdint>
namespace Feather::Math
{
// de Bruijn Sequence: B(2, 5) = 00000111011111001011010100110001. Contains all 32 distinct 5-bit strings.
constexpr uint32_t DE_BRUIJN_SEQ = 0x077CB531U;
constexpr int MULTIPLY_DE_BRUIJN_BIT_POSITION[32] = {0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, 31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9};
// Is x a power of two?
inline constexpr bool IsPowerOf2(int x)
{
return x != 0 && (x & (x - 1)) == 0;
}
// Smallest number 2^z that is greater than or equal to x
// Precondition: x > 0
inline constexpr int RoundToPowerOf2(int x)
{
x--;
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
return x + 1;
}
inline constexpr int CeilLog2(int x)
{
// Ensure x is power of 2
x = IsPowerOf2(x) ? x : RoundToPowerOf2(x);
// The de Bruijn sequence contains all 32 distinct 5-bit strings
// 27 is 32 - 5 and 0x1F (31) is the lower 5 bits 0001 1111
return MULTIPLY_DE_BRUIJN_BIT_POSITION[(int)((int64_t)x * DE_BRUIJN_SEQ >> 27) & 0x1F];
}
// log base 2
inline constexpr int Log2(int x)
{
return CeilLog2(x) - (IsPowerOf2(x) ? 0 : 1);
}
// Divide and round up
template<typename T>
inline constexpr T CeilDiv(const T a, const T b)
{
return (a / b) + (a % b != 0);
}
}