/// <summary>
/// Produces the most rudimentary magic number hash.
/// The returned byte value is composed in two parts: the lower
/// seven bits, and the upper bit. First, the lower seven bits
/// is set to the value of the count of the One-bits in
/// this <paramref name="guid"/>, minus one (therefore, the
/// lower seven bits in the returned byte is the count the one-bits,
/// from zero to 127; and if there are either zero or one One-bits
/// then that value is zero). If those lower seven bits are masked
/// out, it yields the value, [0,127] that is the count of the
/// One-bits, minus one. The last upper bit is set to one if
/// the counr of the One-bits in the first eight bytes in this
/// <paramref name="guid"/> is larger than the count of One-bits
/// in the lower eight bytes --- and is zero if the counts are equal.
/// </summary>
/// <param name="i">Sixteen byte value to hash into one byte.</param>
/// <returns>One byte composed from sixteen.</returns>
public static byte SimpleMaskedByte(this Guid guid)
{
byte[] bytes = guid.ToByteArray();
int bigCount = 0;
int littleCount = 0;
for (int i = 0; i < bytes.Length; ++i)
{
if (i < 8)
{
littleCount += ByteFlags.CountBits(bytes[i]);
}
else
{
bigCount += ByteFlags.CountBits(bytes[i]);
}
}
int value = (bigCount + littleCount) - 1;
if (bigCount > littleCount)
{
value |= 128;
}
return((byte)value);
}
/// <summary>
/// Produces the most rudimentary magic number hash.
/// The returned ushort value is composed in two parts: the lower
/// eight bits, and the upper eight. First, the lower eight bits
/// is simply set to the value of the count of the One-bits in
/// this <paramref name="guid"/>. If those lower eight bits are
/// masked out, it yields the value, [0,128] that is the count of the
/// One-bits. The upper eight bits are set individually, by counting
/// the One-bits in each two-byte pair of bytes from the
/// <paramref name="guid"/>. The upper msb byte is set to one
/// if the count of One-bits in the first two bytes from the Guid
/// is larger than the count of zero-bits --- and is zero if the
/// counts are equal. The following seven bits are then set from
/// the foloowing counts of the two-byte pairs: the ushort byte
/// is set to one if the count of One-bits in the two-byte pair
/// from the Guid is larger than the count of zero-bits.
/// </summary>
/// <param name="i">Sixteen byte value to hash into two bytes.</param>
/// <returns>Two bytes composed from sixteen.</returns>
public static ushort SimpleMaskedShort(this Guid guid)
{
byte[] bytes = guid.ToByteArray();
int count = 0;
foreach (byte b in bytes)
{
count += ByteFlags.CountBits(b);
}
ByteFlags flags = new ByteFlags();
for (int i = 0, j = 8; i < bytes.Length - 1; i += 2, --j)
{
if ((ByteFlags.CountBits(bytes[i])
+ ByteFlags.CountBits(bytes[i + 1]))
> 8)
{
flags.Set(j);
}
}
return((ushort)(count | (flags.Flags << 8)));
}