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using System.Runtime.CompilerServices;
namespace ARMeilleure.Common
{
static class BitUtils
{
private const int DeBrujinSequence = 0x77cb531;
private static int[] DeBrujinLbsLut;
static BitUtils()
{
DeBrujinLbsLut = new int[32];
for (int index = 0; index < DeBrujinLbsLut.Length; index++)
{
uint lutIndex = (uint)(DeBrujinSequence * (1 << index)) >> 27;
DeBrujinLbsLut[lutIndex] = index;
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static int LowestBitSet(int value)
{
if (value == 0)
{
return -1;
}
int lsb = value & -value;
return DeBrujinLbsLut[(uint)(DeBrujinSequence * lsb) >> 27];
}
public static int HighestBitSet(int value)
{
if (value == 0)
{
return -1;
}
for (int bit = 31; bit >= 0; bit--)
{
if (((value >> bit) & 1) != 0)
{
return bit;
}
}
return -1;
}
private static readonly sbyte[] HbsNibbleLut = { -1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3 };
public static int HighestBitSetNibble(int value) => HbsNibbleLut[value & 0b1111];
public static long Replicate(long bits, int size)
{
long output = 0;
for (int bit = 0; bit < 64; bit += size)
{
output |= bits << bit;
}
return output;
}
public static int CountBits(int value)
{
int count = 0;
while (value != 0)
{
value &= ~(value & -value);
count++;
}
return count;
}
public static long FillWithOnes(int bits)
{
return bits == 64 ? -1L : (1L << bits) - 1;
}
public static int RotateRight(int bits, int shift, int size)
{
return (int)RotateRight((uint)bits, shift, size);
}
public static uint RotateRight(uint bits, int shift, int size)
{
return (bits >> shift) | (bits << (size - shift));
}
public static long RotateRight(long bits, int shift, int size)
{
return (long)RotateRight((ulong)bits, shift, size);
}
public static ulong RotateRight(ulong bits, int shift, int size)
{
return (bits >> shift) | (bits << (size - shift));
}
}
}
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