/* deletes node p from tree */
private static void delete_node(ref encode_state sp, int p)
{
int q;
if (sp.parent[p] == NIL)
{
return; /* not in tree */
}
if (sp.rchild[p] == NIL)
{
q = sp.lchild[p];
}
else if (sp.lchild[p] == NIL)
{
q = sp.rchild[p];
}
else
{
q = sp.lchild[p];
if (sp.rchild[q] != NIL)
{
do
{
q = sp.rchild[q];
} while (sp.rchild[q] != NIL);
sp.rchild[sp.parent[q]] = sp.lchild[q];
sp.parent[sp.lchild[q]] = sp.parent[q];
sp.lchild[q] = sp.lchild[p];
sp.parent[sp.lchild[p]] = q;
}
sp.rchild[q] = sp.rchild[p];
sp.parent[sp.rchild[p]] = q;
}
sp.parent[q] = sp.parent[p];
if (sp.rchild[sp.parent[p]] == p)
{
sp.rchild[sp.parent[p]] = q;
}
else
{
sp.lchild[sp.parent[p]] = q;
}
sp.parent[p] = NIL;
}
/*
* initialize state, mostly the trees
*
* For i = 0 to N - 1, rchild[i] and lchild[i] will be the right and left
* children of node i. These nodes need not be initialized. Also, parent[i]
* is the parent of node i. These are initialized to NIL (= N), which stands
* for 'not used.' For i = 0 to 255, rchild[N + i + 1] is the root of the
* tree for strings that begin with character i. These are initialized to NIL.
* Note there are 256 trees. */
private static void init_state(ref encode_state sp)
{
int i;
sp.lchild = new int[N + 1];
sp.rchild = new int[N + 257];
sp.parent = new int[N + 1];
sp.text_buf = new byte[N + F - 1];
for (i = 0; i < N - F; i++)
{
sp.text_buf[i] = 0;
}
for (i = N + 1; i <= N + 256; i++)
{
sp.rchild[i] = NIL;
}
for (i = 0; i < N; i++)
{
sp.parent[i] = NIL;
}
}
public static byte[] Compress(byte[] src)
{
/* Encoding state, mostly tree but some current match stuff */
encode_state sp = new encode_state();
int i, c, len, r, s, last_match_length, code_buf_ptr;
byte[] code_buf = new byte[17];
byte mask;
init_state(ref sp);
/*
* code_buf[1..16] saves eight units of code, and code_buf[0] works
* as eight flags, "1" representing that the unit is an unencoded
* letter (1 byte), "" a position-and-length pair (2 bytes).
* Thus, eight units require at most 16 bytes of code.
*/
code_buf[0] = 0;
code_buf_ptr = mask = 1;
/* Clear the buffer with any character that will appear often. */
s = 0; r = N - F;
MemoryStream src_stream = new MemoryStream(src);
MemoryStream dst_stream = new MemoryStream();
/* Read F bytes into the last F bytes of the buffer */
for (len = 0; len < F && src_stream.Position < src_stream.Length; len++)
{
sp.text_buf[r + len] = (byte)src_stream.ReadByte();
}
if (len <= 0)
{
return(dst_stream.ToArray()); /* text of size zero */
}
/*
* Insert the F strings, each of which begins with one or more
* 'space' characters. Note the order in which these strings are
* inserted. This way, degenerate trees will be less likely to occur.
*/
for (i = 1; i <= F; i++)
{
insert_node(ref sp, r - i);
}
/*
* Finally, insert the whole string just read.
* The global variables match_length and match_position are set.
*/
insert_node(ref sp, r);
do
{
/* match_length may be spuriously long near the end of text. */
if (sp.match_length > len)
{
sp.match_length = len;
}
if (sp.match_length <= THRESHOLD)
{
sp.match_length = 1; /* Not long enough match. Send one byte. */
code_buf[0] |= mask; /* 'send one byte' flag */
code_buf[code_buf_ptr++] = sp.text_buf[r]; /* Send uncoded. */
}
else
{
/* Send position and length pair. Note match_length > THRESHOLD. */
code_buf[code_buf_ptr++] = (byte)sp.match_position;
code_buf[code_buf_ptr++] = (byte)
(((sp.match_position >> 4) & 0xF0)
| (sp.match_length - (THRESHOLD + 1)));
}
//这里位运算有问题，byte为uint，所以这里取低8位
if (((mask <<= 1) & 0xFF) == 0)
{ /* Shift mask left one bit. */
/* Send at most 8 units of code together */
for (i = 0; i < code_buf_ptr; i++)
{
dst_stream.WriteByte(code_buf[i]);
}
code_buf[0] = 0;
code_buf_ptr = mask = 1;
}
last_match_length = sp.match_length;
for (i = 0; i < last_match_length && src_stream.Position < src_stream.Length; i++)
{
delete_node(ref sp, s); /* Delete old strings and */
c = src_stream.ReadByte();
sp.text_buf[s] = (byte)c; /* read new bytes */
/*
* If the position is near the end of buffer, extend the buffer
* to make string comparison easier.
*/
if (s < F - 1)
{
sp.text_buf[s + N] = (byte)c;
}
/* Since this is a ring buffer, increment the position modulo N. */
s = (s + 1) & (N - 1);
r = (r + 1) & (N - 1);
/* Register the string in text_buf[r..r+F-1] */
insert_node(ref sp, r);
}
while (i++ < last_match_length)
{
delete_node(ref sp, s);
/* After the end of text, no need to read, */
s = (s + 1) & (N - 1);
r = (r + 1) & (N - 1);
/* but buffer may not be empty. */
if (--len >= 0)
{
insert_node(ref sp, r);
}
}
} while (len > 0); /* until length of string to be processed is zero */
if (code_buf_ptr > 1)
{ /* Send remaining code. */
for (i = 0; i < code_buf_ptr; i++)
{
dst_stream.WriteByte(code_buf[i]);
}
}
return(dst_stream.ToArray());
}
/*
* Inserts string of length F, text_buf[r..r+F-1], into one of the trees
* (text_buf[r]'th tree) and returns the longest-match position and length
* via the global variables match_position and match_length.
* If match_length = F, then removes the old node in favor of the new one,
* because the old one will be deleted sooner. Note r plays double role,
* as tree node and position in buffer.
*/
private static void insert_node(ref encode_state sp, int r)
{
int i, p, cmp;
int key;
cmp = 1;
key = r;
p = N + 1 + sp.text_buf[key];
sp.rchild[r] = sp.lchild[r] = NIL;
sp.match_length = 0;
for (; ;)
{
if (cmp >= 0)
{
if (sp.rchild[p] != NIL)
{
p = sp.rchild[p];
}
else
{
sp.rchild[p] = r;
sp.parent[r] = p;
return;
}
}
else
{
if (sp.lchild[p] != NIL)
{
p = sp.lchild[p];
}
else
{
sp.lchild[p] = r;
sp.parent[r] = p;
return;
}
}
for (i = 1; i < F; i++)
{
if ((cmp = sp.text_buf[key + i] - sp.text_buf[p + i]) != 0)
{
break;
}
}
if (i > sp.match_length)
{
sp.match_position = p;
if ((sp.match_length = i) >= F)
{
break;
}
}
}
sp.parent[r] = sp.parent[p];
sp.lchild[r] = sp.lchild[p];
sp.rchild[r] = sp.rchild[p];
sp.parent[sp.lchild[p]] = r;
sp.parent[sp.rchild[p]] = r;
if (sp.rchild[sp.parent[p]] == p)
{
sp.rchild[sp.parent[p]] = r;
}
else
{
sp.lchild[sp.parent[p]] = r;
}
sp.parent[p] = NIL; /* remove p */
}
