/// <summary>
/// Calculates the <see cref="Fletcher32Checksum"/> of a <see cref="UInt16"/>[]. This method implements the slow but straightforward way.
/// This algorithm is also known as the "16-bit Fletcher Checksum", since it consumes the data word in 16-bit chunks.
/// </summary>
/// <param name="data">The list whose elements shall be added to the checksum.</param>
/// <param name="offset">Location in the array.</param>
/// <param name="count">Number of elements.</param>
/// <param name="fletcher32">The <see cref="Fletcher32Checksum"/> to start from.</param>
/// <returns>A <see cref="Fletcher32Checksum"/>.</returns>
public static Fletcher32Checksum GetSlow(IList<ushort> data, int offset = 0, int count = 0, Fletcher32Checksum fletcher32 = new Fletcher32Checksum())
{
if (data == null) throw new ArgumentNullException("data");
if (offset < 0 || offset > data.Count) throw new ArgumentOutOfRangeException("offset", "Must be non-negative and less than or equal to the length of data.");
if (count < 0) throw new ArgumentOutOfRangeException("count", "Must be non-negative.");
if (offset + count > data.Count) throw new ArgumentOutOfRangeException("count", "Must be less than or equal to the length of data minus the offset argument.");
if (count == 0)
{
count = data.Count - offset;
if (count == 0) return fletcher32;
}
int c0 = fletcher32.C0;
int c1 = fletcher32.C1;
for (int i = offset; i < count; i++)
{
c0 = (c0 + data[i]) % 65535;
c1 = (c1 + c0) % 65535;
}
return new Fletcher32Checksum() { C0 = (ushort)c0, C1 = (ushort)c1 };
}
/// <summary>
/// Calculates the <see cref="Fletcher32Checksum"/> of a <see cref="UInt16"/>[].
/// This algorithm is also known as the "16-bit Fletcher Checksum", since it consumes the data word in 16-bit chunks.
/// </summary>
/// <param name="data">An array of <see cref="UInt16"/>s.</param>
/// <param name="offset">Location in the array.</param>
/// <param name="count">Number of elements.</param>
/// <param name="fletcher32">The <see cref="Fletcher32Checksum"/> to start from.</param>
/// <returns>A <see cref="Fletcher32Checksum"/>.</returns>
public static Fletcher32Checksum Get(ushort[] data, int offset = 0, int count = 0, Fletcher32Checksum fletcher32 = new Fletcher32Checksum())
{
if (data == null) throw new ArgumentNullException("data");
if (offset < 0 || offset > data.Length) throw new ArgumentOutOfRangeException("offset", "Must be non-negative and less than or equal to the length of data.");
if (count < 0) throw new ArgumentOutOfRangeException("count", "Must be non-negative.");
if (offset + count > data.Length) throw new ArgumentOutOfRangeException("count", "Must be less than or equal to the length of data minus the offset argument.");
if (count == 0)
{
count = data.Length - offset;
if (count == 0) return fletcher32;
}
uint c0 = fletcher32.C0;
uint c1 = fletcher32.C1;
unsafe
{
// local copies of values and references make the code much faster
int lCount = count;
fixed(ushort* lDataFixed=data)
{
ushort* lData = lDataFixed + offset;
while (lCount > 0)
{
int c = lCount > 359 ? 359 : lCount;
lCount -= c;
do
{
c0 += *lData++;
c1 += c0;
}
while(--c > 0);
c1 = (c1 & 0xffff) + (c1 >> 16);
c0 = (c0 & 0xffff) + (c0 >> 16);
}
}
}
// once again, to reduce the sums to 16 bits, each
c0 = (c0 & 0xffff) + (c0 >> 16);
c1 = (c1 & 0xffff) + (c1 >> 16);
return new Fletcher32Checksum() { C0 = (ushort)c0, C1 = (ushort)c1 };
}
/// <summary>
/// Calculates the <see cref="Fletcher32Checksum"/> of a <see cref="IEnumerable{UInt16}"/>. This method implements the slow but straightforward way.
/// This algorithm is also known as the "16-bit Fletcher Checksum", since it consumes the data word in 16-bit chunks.
/// </summary>
/// <param name="data">The collection whose elements shall be added to the checksum.</param>
/// <param name="fletcher32">The <see cref="Fletcher32Checksum"/> to start from.</param>
/// <returns>A <see cref="Fletcher32Checksum"/>.</returns>
public static Fletcher32Checksum GetSlow(IEnumerable<ushort> data, Fletcher32Checksum fletcher32 = new Fletcher32Checksum())
{
if (data == null) throw new ArgumentNullException("data");
int c0 = fletcher32.C0;
int c1 = fletcher32.C1;
foreach (ushort value in data)
{
c0 = (c0 + value) % 65535;
c1 = (c1 + c0) % 65535;
}
return new Fletcher32Checksum() { C0 = (ushort)c0, C1 = (ushort)c1 };
}
/// <summary>
/// Calculates the <see cref="Fletcher32Checksum"/> of a <see cref="IEnumerable{UInt16}"/>.
/// This algorithm is also known as the "16-bit Fletcher Checksum", since it consumes the data word in 16-bit chunks.
/// </summary>
/// <param name="data">The collection whose elements shall be added to the checksum.</param>
/// <param name="fletcher32">The <see cref="Fletcher32Checksum"/> to start from.</param>
/// <returns>A <see cref="Fletcher32Checksum"/>.</returns>
public static Fletcher32Checksum Get(IEnumerable<ushort> data, Fletcher32Checksum fletcher32 = new Fletcher32Checksum())
{
if (data == null) throw new ArgumentNullException("data");
uint c0 = fletcher32.C0;
uint c1 = fletcher32.C1;
// local copies of values and references make the code much faster
IEnumerable<ushort> lData = data;
int c = 0;
foreach (ushort value in lData)
{
c0 += value;
c1 += c0;
if ((++c) <= 359) continue;
c = 0;
c1 = (c1 & 0xffff) + (c1 >> 16);
c0 = (c0 & 0xffff) + (c0 >> 16);
}
if (c != 0)
{
c1 = (c1 & 0xffff) + (c1 >> 16);
c0 = (c0 & 0xffff) + (c0 >> 16);
}
// once again, to reduce the sums to 16 bits, each
c0 = (c0 & 0xffff) + (c0 >> 16);
c1 = (c1 & 0xffff) + (c1 >> 16);
return new Fletcher32Checksum() { C0 = (ushort)c0, C1 = (ushort)c1 };
}
