public static IList <byte> MTF(IList <byte> bytes)
{
var mtf = new MoveToFront(bytes);
var mtfResult = mtf.InverseTransform();
return(mtfResult);
}
// Performs the Move To Front transform and Run Length Encoding[1] stages
public void Encode()
{
var huffmanSymbolMap = new byte[256];
var symbolMTF = new MoveToFront();
int totalUniqueValues = 0;
for (var i = 0; i < 256; i++) {
if (bwtValuesInUse[i])
huffmanSymbolMap[i] = (byte) totalUniqueValues++;
}
int endOfBlockSymbol = totalUniqueValues + 1;
int mtfIndex = 0;
int repeatCount = 0;
int totalRunAs = 0;
int totalRunBs = 0;
for (var i = 0; i < bwtLength; i++)
{
// Move To Front
int mtfPosition = symbolMTF.ValueToFront(huffmanSymbolMap[bwtBlock[i] & 0xff]);
// Run Length Encode
if (mtfPosition == 0) {
repeatCount++;
} else {
if (repeatCount > 0)
{
repeatCount--;
while (true)
{
if ((repeatCount & 1) == 0)
{
mtfBlock[mtfIndex++] = RLE_SYMBOL_RUNA;
totalRunAs++;
} else {
mtfBlock[mtfIndex++] = RLE_SYMBOL_RUNB;
totalRunBs++;
}
if (repeatCount <= 1)
break;
repeatCount = (repeatCount - 2) >> 1;
}
repeatCount = 0;
}
mtfBlock[mtfIndex++] = (char) (mtfPosition + 1);
mtfSymbolFrequencies[mtfPosition + 1]++;
}
}
if (repeatCount > 0) {
repeatCount--;
while (true)
{
if ((repeatCount & 1) == 0) {
mtfBlock[mtfIndex++] = RLE_SYMBOL_RUNA;
totalRunAs++;
} else {
mtfBlock[mtfIndex++] = RLE_SYMBOL_RUNB;
totalRunBs++;
}
if (repeatCount <= 1)
break;
repeatCount = (repeatCount - 2) >> 1;
}
}
mtfBlock[mtfIndex] = (ushort)endOfBlockSymbol;
mtfSymbolFrequencies[endOfBlockSymbol]++;
mtfSymbolFrequencies[RLE_SYMBOL_RUNA] += totalRunAs;
mtfSymbolFrequencies[RLE_SYMBOL_RUNB] += totalRunBs;
this.MtfLength = mtfIndex + 1;
this.MtfAlphabetSize = endOfBlockSymbol + 1;
}
