public void EmptyPrefixTableTest()
{
PrefixTable pt = new PrefixTable();
int length;
Assert.AreEqual(-1, pt.Find(new byte[0], 0, out length));
Assert.AreEqual(0, length);
Assert.AreEqual(-1, pt.Find(new byte[1] { 0 }, 0, out length));
Assert.AreEqual(0, length);
Assert.AreEqual(-1, pt.Find(new byte[1] { 1 }, 0, out length));
Assert.AreEqual(0, length);
}
public void OneBytePrefixTableTest()
{
PrefixTable pt = new PrefixTable();
int length;
for (int n = 0; n < 16; ++n) {
pt.Add(n, -1, (byte)n);
}
for (int n = 0; n < 16; ++n) {
Assert.AreEqual(n, pt.Find(new byte[1] { (byte)n }, 0, out length), "checking code");
Assert.AreEqual(1, length, "checking length");
}
Assert.AreEqual(-1, pt.Find(new byte[1] { 17 }, 0, out length), "checking code not found");
Assert.AreEqual(0, length, "checking length not found");
}
public void OffsetPrefixTableTest()
{
PrefixTable pt = new PrefixTable();
int length;
pt.Add(0, -1, 0);
pt.Add(1, 0, 1);
pt.Add(2, 0, 2);
pt.Add(3, 0, 3);
Assert.AreEqual(1, pt.Find(new byte[7] { 0, 1, 0, 2, 0, 3, 99 }, 0, out length));
Assert.AreEqual(2, length);
Assert.AreEqual(2, pt.Find(new byte[7] { 0, 1, 0, 2, 0, 3, 99 }, 2, out length));
Assert.AreEqual(2, length);
Assert.AreEqual(3, pt.Find(new byte[7] { 0, 1, 0, 2, 0, 3, 99 }, 4, out length));
Assert.AreEqual(2, length);
}
public void DivergentPrefixTableTest()
{
PrefixTable pt = new PrefixTable();
int length;
pt.Add(0, -1, 0);
pt.Add(1, 0, 1);
pt.Add(2, 0, 2);
pt.Add(3, 0, 3);
Assert.AreEqual(0, pt.Find(new byte[2] { 0, 99 }, 0, out length));
Assert.AreEqual(1, length);
Assert.AreEqual(1, pt.Find(new byte[3] { 0, 1, 99 }, 0, out length));
Assert.AreEqual(2, length);
Assert.AreEqual(2, pt.Find(new byte[3] { 0, 2, 99 }, 0, out length));
Assert.AreEqual(2, length);
Assert.AreEqual(3, pt.Find(new byte[3] { 0, 3, 99 }, 0, out length));
Assert.AreEqual(2, length);
}
private void WriteImageData(Image image)
{
// Figure out which color table is in use and deduce the code size
ColorTable colorTable = image.LocalColorTable ?? GlobalColorTable;
int colorTableBitSize = colorTable.BitSize();
int codeSize = (colorTableBitSize == 1 ? 2 : colorTableBitSize);
if (Debug) {
Console.Error.WriteLine("Writing code size {0} bits", codeSize);
}
WriteByte(codeSize);
// Initial code length is one more than code size, to accomodate the
// Clear and End codes.
BitWriter writer = new BitWriter()
{
Output = Output,
CodeLength = 1 + codeSize,
Debug = this.Debug,
};
// Initialize the prefix table with matches for all single-unit codes
PrefixTable prefixes = new PrefixTable();
for (int n = 0; n < (1 << codeSize); ++n) {
prefixes.Add(n, -1, (byte)n);
}
int minCode = (1 << codeSize) + 2;
int nextCode = minCode;
// Start with a Clear. (Pointless - the decoder knows perfectly well what
// the initial state is.)
if (Debug) {
Console.Error.WriteLine("Bit-writing clear marker {0}", 1 << codeSize);
}
writer.WriteBits(1 << codeSize);
int pos = 0;
if (Debug) {
Console.Error.WriteLine("Bit-writing {0} pixels of image data", image.ImageData.Length);
}
while (pos < image.ImageData.Length) {
// Find the longest known prefix that matches this point in the image data
int bestLength;
int bestCode = prefixes.Find(image.ImageData, pos, out bestLength);
// Output the best code we found
writer.WriteBits(bestCode);
// Add a new dictionary entry
if (nextCode < 4096 && pos + bestLength < image.ImageData.Length) {
if (Debug) {
Console.Error.WriteLine("Define code {0:X} as code {1:X} + byte {2:X2}", nextCode, bestCode, image.ImageData[pos + bestLength]);
}
prefixes.Add(nextCode, bestCode, image.ImageData[pos + bestLength]);
// Update the output bit size
if(nextCode >= (1 << writer.CodeLength)) {
++writer.CodeLength;
}
++nextCode;
}
pos += bestLength;
}
// Finish with an End. (Also pointless - the decoder knows what size the image data should be.)
if (Debug) {
Console.Error.WriteLine("Bit-writing end marker {0}", (1 << codeSize) + 1);
}
writer.WriteBits((1 << codeSize) + 1);
if (Debug) {
Console.Error.WriteLine("Flushing bits");
}
writer.FlushBits();
if (Debug) {
Console.Error.WriteLine("Flushing bytes");
}
writer.FlushBytes();
// A zero-sized sub-block terminates.
if (Debug) {
Console.Error.WriteLine("Writing image terminator");
}
WriteByte(0);
}
private void WriteImageData(Image image)
{
// Figure out which color table is in use and deduce the code size
ColorTable colorTable = image.LocalColorTable ?? GlobalColorTable;
int colorTableBitSize = colorTable.BitSize();
int codeSize = (colorTableBitSize == 1 ? 2 : colorTableBitSize);
if (Debug)
{
Console.Error.WriteLine("Writing code size {0} bits", codeSize);
}
WriteByte(codeSize);
// Initial code length is one more than code size, to accomodate the
// Clear and End codes.
BitWriter writer = new BitWriter()
{
Output = Output,
CodeLength = 1 + codeSize,
Debug = this.Debug,
};
// Initialize the prefix table with matches for all single-unit codes
PrefixTable prefixes = new PrefixTable();
for (int n = 0; n < (1 << codeSize); ++n)
{
prefixes.Add(n, -1, (byte)n);
}
int minCode = (1 << codeSize) + 2;
int nextCode = minCode;
// Start with a Clear. (Pointless - the decoder knows perfectly well what
// the initial state is.)
if (Debug)
{
Console.Error.WriteLine("Bit-writing clear marker {0}", 1 << codeSize);
}
writer.WriteBits(1 << codeSize);
int pos = 0;
if (Debug)
{
Console.Error.WriteLine("Bit-writing {0} pixels of image data", image.ImageData.Length);
}
while (pos < image.ImageData.Length)
{
// Find the longest known prefix that matches this point in the image data
int bestLength;
int bestCode = prefixes.Find(image.ImageData, pos, out bestLength);
// Output the best code we found
writer.WriteBits(bestCode);
// Add a new dictionary entry
if (nextCode < 4096 && pos + bestLength < image.ImageData.Length)
{
if (Debug)
{
Console.Error.WriteLine("Define code {0:X} as code {1:X} + byte {2:X2}", nextCode, bestCode, image.ImageData[pos + bestLength]);
}
prefixes.Add(nextCode, bestCode, image.ImageData[pos + bestLength]);
// Update the output bit size
if (nextCode >= (1 << writer.CodeLength))
{
++writer.CodeLength;
}
++nextCode;
}
pos += bestLength;
}
// Finish with an End. (Also pointless - the decoder knows what size the image data should be.)
if (Debug)
{
Console.Error.WriteLine("Bit-writing end marker {0}", (1 << codeSize) + 1);
}
writer.WriteBits((1 << codeSize) + 1);
if (Debug)
{
Console.Error.WriteLine("Flushing bits");
}
writer.FlushBits();
if (Debug)
{
Console.Error.WriteLine("Flushing bytes");
}
writer.FlushBytes();
// A zero-sized sub-block terminates.
if (Debug)
{
Console.Error.WriteLine("Writing image terminator");
}
WriteByte(0);
}