Claunia.ReedSolomon/Claunia.ReedSolomon/OutputInputByteTableCodingLoop.cs

/**
 * One specific ordering/nesting of the coding loops.
 *
 * Copyright 2015, Backblaze, Inc.  All rights reserved.
 * Copyright © 2019 Natalia Portillo
 */

namespace Claunia.ReedSolomon
{
    public class OutputInputByteTableCodingLoop : CodingLoopBase
    {
        public override void CodeSomeShards(byte[][] matrixRows, byte[][] inputs, int inputCount, byte[][] outputs,
                                            int outputCount, int offset, int byteCount)
        {
            byte[][] table = Galois.MULTIPLICATION_TABLE;

            for(int iOutput = 0; iOutput < outputCount; iOutput++)
            {
                byte[] outputShard = outputs[iOutput];
                byte[] matrixRow   = matrixRows[iOutput];

                {
                    int    iInput       = 0;
                    byte[] inputShard   = inputs[iInput];
                    byte[] multTableRow = table[matrixRow[iInput] & 0xFF];

                    for(int iByte = offset; iByte < offset + byteCount; iByte++)
                        outputShard[iByte] = multTableRow[inputShard[iByte] & 0xFF];
                }

                for(int iInput = 1; iInput < inputCount; iInput++)
                {
                    byte[] inputShard   = inputs[iInput];
                    byte[] multTableRow = table[matrixRow[iInput] & 0xFF];

                    for(int iByte = offset; iByte < offset + byteCount; iByte++)
                        outputShard[iByte] ^= multTableRow[inputShard[iByte] & 0xFF];
                }
            }
        }

        public override bool CheckSomeShards(byte[][] matrixRows, byte[][] inputs, int inputCount, byte[][] toCheck,
                                             int checkCount, int offset, int byteCount, byte[] tempBuffer)
        {
            if(tempBuffer == null)
                return base.CheckSomeShards(matrixRows, inputs, inputCount, toCheck, checkCount, offset, byteCount,
                                            null);

            byte[][] table = Galois.MULTIPLICATION_TABLE;

            for(int iOutput = 0; iOutput < checkCount; iOutput++)
            {
                byte[] outputShard = toCheck[iOutput];
                byte[] matrixRow   = matrixRows[iOutput];

                {
                    int    iInput       = 0;
                    byte[] inputShard   = inputs[iInput];
                    byte[] multTableRow = table[matrixRow[iInput] & 0xFF];

                    for(int iByte = offset; iByte < offset + byteCount; iByte++)
                        tempBuffer[iByte] = multTableRow[inputShard[iByte] & 0xFF];
                }

                for(int iInput = 1; iInput < inputCount; iInput++)
                {
                    byte[] inputShard   = inputs[iInput];
                    byte[] multTableRow = table[matrixRow[iInput] & 0xFF];

                    for(int iByte = offset; iByte < offset + byteCount; iByte++)
                        tempBuffer[iByte] ^= multTableRow[inputShard[iByte] & 0xFF];
                }

                for(int iByte = offset; iByte < offset + byteCount; iByte++)
                    if(tempBuffer[iByte] != outputShard[iByte])
                        return false;
            }

            return true;
        }
    }
}