// C# port of the ccitt.c/ccitt.h files in this directory.
// Original files generated by pycrc v0.9, https://pycrc.org

namespace Checksums {
	public static class Ccitt {
		/**
		 * Calculate the initial crc value.
		 *
		 * \return     The initial crc value.
		 *****************************************************************************/
		public static ushort Init() {
			return 0xffff;
		}

		/**
		 * Update the crc value with new data.
		 *
		 * \param crc      The current crc value.
		 * \param data     Pointer to a buffer of \a data_len bytes.
		 * \param data_len Number of bytes in the \a data buffer.
		 * \return         The updated crc value.
		 *****************************************************************************/
		public static ushort Update( ushort crc, byte[] data, long data_len ) {
			uint i;
			bool bit;
			byte c;

			for ( long idx = 0; idx < data_len;  ++idx ) {
				c = data[idx];
				for ( i = 0x80; i > 0; i >>= 1 ) {
					bit = ( crc & 0x8000 ) != 0;
					if ( ( c & i ) != 0 ) {
						bit = !bit;
					}
					crc <<= 1;
					if ( bit ) {
						crc ^= 0x1021;
					}
				}
				crc &= 0xffff;
			}
			return (ushort)( crc & 0xffff );
		}

		/**
		 * Calculate the final crc value.
		 *
		 * \param crc  The current crc value.
		 * \return     The final crc value.
		 *****************************************************************************/
		public static ushort Finalize( ushort crc ) {
			return (ushort)( crc ^ 0x0000 );
		}
	}
}