public static int Decode(byte[] source, int sourceOffset, int sourceLength, byte[] destination, int destinationOffset, int destinationLength)
{
// Get the uncompressed size
var len = VarInt.UvarInt(source, sourceOffset);
// Destination array doesn't have enough room for the decoded data.
if (destinationLength < (int)len.Value)
{
throw new IndexOutOfRangeException("snappy: destination array too short");
}
// Adjust the lengths
sourceLength += sourceOffset;
destinationLength += destinationOffset;
// Current offsets
int s = sourceOffset + len.VarIntLength;
int d = destinationOffset;
int offset = 0;
int length = 0;
while (s < sourceLength)
{
byte tag = (byte)(source[s] & 0x03);
if (tag == SnappyTag.Literal)
{
uint x = (uint)(source[s] >> 2);
if (x < 60)
{
s += 1;
}
else if (x == 60)
{
s += 2;
if (s > sourceLength)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
x = (uint)source[s - 1];
}
else if (x == 61)
{
s += 3;
if (s > sourceLength)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
x = (uint)source[s - 2] | (uint)source[s - 1] << 8;
}
else if (x == 62)
{
s += 4;
if (s > sourceLength)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
x = (uint)source[s - 3] | (uint)source[s - 2] << 8 | (uint)source[s - 1] << 16;
}
else if (x == 63)
{
s += 5;
if (s > sourceLength)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
x = (uint)source[s - 4] | (uint)source[s - 3] << 8 | (uint)source[s - 2] << 16 | (uint)source[s - 1] << 24;
}
length = (int)(x + 1);
if (length <= 0)
{
throw new IndexOutOfRangeException("snappy: unsupported literal length");
}
if (length > destinationLength - d || length > sourceOffset + sourceLength - s)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
Array.Copy(source, s, destination, d, length);
d += length;
s += length;
continue;
}
else if (tag == SnappyTag.Copy1)
{
s += 2;
if (s > sourceOffset + sourceLength)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
length = 4 + (((int)source[s - 2] >> 2) & 0x7);
offset = ((int)source[s - 2] & 0xe0) << 3 | (int)source[s - 1];
}
else if (tag == SnappyTag.Copy2)
{
s += 3;
if (s > sourceOffset + sourceLength)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
length = 1 + ((int)source[s - 3] >> 2);
offset = (int)source[s - 2] | (int)source[s - 1] << 8;
}
else if (tag == SnappyTag.Copy4)
{
throw new NotSupportedException("snappy: unsupported COPY_4 tag");
}
int end = d + length;
if (offset > d || end > destinationLength)
{
throw new IndexOutOfRangeException("snappy: corrupt input");
}
for (; d < end; d++)
{
destination[d] = destination[d - offset];
}
}
return(d);
}
/// <summary>
/// Encodes the buffer into the stream provided.
/// </summary>
/// <param name="source">The source buffer.</param>
/// <param name="sourceOffset">The offset to start encoding.</param>
/// <param name="sourceLength">The number of bytes to encode.</param>
/// <param name="destination">The destination to write into.</param>
/// <param name="destinationOffset">The offset to start writing into.</param>
/// <returns></returns>
public int Encode(byte[] source, int sourceOffset, int sourceLength, BufferSegment destination, int destinationOffset)
{
if (destination.Size - destinationOffset < MaxEncodedLen(sourceLength))
{
throw new IndexOutOfRangeException("Snappy destination array too short.");
}
// The block starts with the varint-encoded length of the decompressed bytes.
var start = this.Index = destination.Offset + destinationOffset;
this.Index += VarInt.WriteTo(destination, this.Index, (ulong)sourceLength);
// Return early if src is short.
if (sourceLength <= 4 && sourceLength != 0)
{
EmitLiteral(destination, source, sourceOffset, sourceLength);
return(this.Index - start);
}
// Initialize the hash table. Its size ranges from 1<<8 to 1<<14 inclusive.
int shift = 32 - 8;
uint tableSize = 1 << 8;
while (tableSize < MaxTableSize && tableSize < sourceLength)
{
shift--;
tableSize *= 2;
}
// Clear the table up until we're going to use it, to save time
Array.Clear(Table, 0, (int)tableSize);
// Iterate over the source bytes.
int s = sourceOffset;
int t = 0;
int lit = sourceOffset;
while (s + 3 < sourceLength)
{
// Update the hash table.
byte b0 = source[s];
byte b1 = source[s + 1];
byte b2 = source[s + 2];
byte b3 = source[s + 3];
uint h = (uint)b0 | ((uint)b1) << 8 | ((uint)b2) << 16 | ((uint)b3) << 24;
var p = (h * 0x1e35a7bd) >> shift;
// We need to to store values in [-1, inf) in table. To save
// some initialization time, (re)use the table's zero value
// and shift the values against this zero: add 1 on writes,
// subtract 1 on reads.
t = this.Table[p] - 1;
this.Table[p] = s + 1;
// If t is invalid or src[s:s+4] differs from src[t:t+4],
// accumulate a literal byte.
if (t < 0 || s - t >= MaxOffset || b0 != source[t] || b1 != source[t + 1] || b2 != source[t + 2] || b3 != source[t + 3])
{
s++;
continue;
}
// Otherwise, we have a match. First, emit any pending literal bytes.
if (lit != s)
{
EmitLiteral(destination, source, lit, s - lit);
}
// Extend the match to be as long as possible.
int s0 = s;
s = s + 4;
t = t + 4;
while (s < sourceLength && source[s] == source[t])
{
s++;
t++;
}
// Emit the copied bytes.
EmitCopy(destination, s - t, s - s0 + sourceOffset);
lit = s;
}
// Emit any final pending literal bytes and return.
if (lit != sourceLength)
{
EmitLiteral(destination, source, lit, sourceLength - lit);
}
return(this.Index - start);
}
