/// <summary>
/// Method used for compression of a suffix array based on Delta encoding algorithm.
/// This method is also using Psi function. See <see cref="PsiFunction.GeneratePsiFunction(int[], string)"/>.
/// </summary>
/// <param name="input">String which will be compressed.</param>
/// <returns>Dictionary of compressed values divided by characters from the original input.</returns>
public static Dictionary <char, List <Int16> > DeltaEncodingCompression(string input)
{
Dictionary <char, List <int> > incSequences = PsiFunction.GetIncreasingSequences(input);
Dictionary <char, List <Int16> > deltaEncoding = new Dictionary <char, List <Int16> >();
List <Int16> deltaSequence;
foreach (var key in incSequences.Keys)
{
deltaSequence = new List <Int16>();
deltaSequence.Add(Convert.ToInt16(incSequences[key].ElementAt(0)));
deltaEncoding.Add(key, deltaSequence);
}
foreach (var key in incSequences.Keys)
{
deltaSequence = new List <Int16>();
deltaSequence = deltaEncoding[key];
for (int i = 0; i < incSequences[key].Count - 1; i++)
{
deltaSequence.Add(Convert.ToInt16(incSequences[key].ElementAt(i + 1) - incSequences[key].ElementAt(i)));
}
deltaEncoding[key] = deltaSequence;
}
return(deltaEncoding);
}
/// <summary>
/// Method used for compression of a suffix array based on Elias-Fano algorithm.
/// </summary>
/// <param name="input">Original input.</param>
/// <param name="bitLengthOfSeq">List of values that represent length of resulting bit sequences by increasing sequences.</param>
/// <param name="bitLengthOfOrigParts">List of integer arrays containing information about length of leading and lower bit sequences.</param>
/// <returns>List of bytes which represent compressed values.</returns>
public static List <byte[]> EliasFanoCompression(string input, List <int> bitLengthOfSeq, List <int[]> bitLengthOfOrigParts)
{
Dictionary <char, List <int> > incSequences = PsiFunction.GetIncreasingSequences(input);
List <bool[]> eliasFano = new List <bool[]>();
int eliasIndex = 0;
int m;
int noOfBits = 0;
int noOfLeadingBits;
int noOfLowerBits;
int[] bucket;
bool[] lowerBits;
bool[] leadingBits;
bool[] number;
bool[] lowerEliasFano;
bool[] leadingEliasFano;
foreach (var val in incSequences.Values)
{
int lowerPointer = 0;
m = val[val.Count - 1];
noOfBits = BitsToExpressNumber(val[val.Count - 1]);
noOfLeadingBits = GetNumberOfLeadingBits(val.Count);
bucket = new int[(int)Math.Pow(2, noOfLeadingBits)];
noOfLowerBits = noOfBits - noOfLeadingBits;
int[] bits = new int[2];
bits[0] = noOfLeadingBits;
bits[1] = noOfLowerBits;
bitLengthOfOrigParts.Insert(eliasIndex, bits);
lowerEliasFano = new bool[val.Count * noOfLowerBits];
foreach (var item in val)
{
number = new bool[noOfBits];
lowerBits = new bool[noOfLowerBits];
leadingBits = new bool[noOfLeadingBits];
number = NumberToBits(item, noOfBits);
int j = 0;
for (int i = 0; i < noOfBits; i++)
{
if (i < noOfLeadingBits)
{
leadingBits[i] = number[i];
}
else
{
lowerBits[j++] = number[i];
}
}
bucket[GetNumberFromBits(leadingBits)]++;
for (int i = 0; i < noOfLowerBits; i++)
{
lowerEliasFano[lowerPointer++] = lowerBits[i];
}
}
int sizeOfLeading = 0;
foreach (var counter in bucket)
{
sizeOfLeading += counter + 1;
}
leadingEliasFano = new bool[sizeOfLeading];
GenerateLeadingSequence(bucket, leadingEliasFano);
bool[] resultVector = GenerateResultVectorOfBits(sizeOfLeading + val.Count * noOfLowerBits,
leadingEliasFano, lowerEliasFano);
eliasFano.Insert(eliasIndex, resultVector);
eliasIndex++;
}
int f = 0;
foreach (var seq in eliasFano)
{
bitLengthOfSeq.Insert(f, seq.Length);
f++;
}
return(EncodeToBytes(eliasFano));
}
