/// <summary>
/// Map from a distance to a distance code.
/// </summary>
/// <remarks>No side effects. _dist_code[256] and _dist_code[257] are never used.</remarks>
internal static int DistanceCode(int dist)
{
return dist < 256
? _dist_code[dist]
: _dist_code[256 + SharedUtils.URShift(dist, 7)];
}
int huft_build(int[] b, int bindex, int n, int s, int[] d, int[] e, int[] t, int[] m, int[] hp, int[] hn,
int[] v)
{
// Given a list of code lengths and a maximum table size, make a set of tables to decode
// that set of codes. Return Z_OK on success, Z_BUF_ERROR if the given code set is
// incomplete (the tables are still built in this case), Z_DATA_ERROR if the input is
// invalid (an over-subscribed set of lengths), or Z_MEM_ERROR if not enough memory.
int a; // counter for codes of length k
int f; // i repeats in table every f entries
int g; // maximum code length
int h; // table level
int i; // counter, current code
int j; // counter
int k; // number of bits in current code
int l; // bits per table (returned in m)
int mask; // (1 << w) - 1, to avoid cc -O bug on HP
int p; // pointer into c[], b[], or v[]
int q; // points to current table
int w; // bits before this table == (l * h)
int xp; // pointer into x
int y; // number of dummy codes added
int z; // number of entries in current table
// Generate counts for each bit length
p = 0;
i = n;
do
{
c[b[bindex + p]]++;
p++;
i--; // assume all entries <= BMAX
}while (i != 0);
if (c[0] == n)
{
// null input--all zero length codes
t[0] = -1;
m[0] = 0;
return(Z_OK);
}
// Find minimum and maximum length, bound *m by those
l = m[0];
for (j = 1; j <= BMAX; j++)
{
if (c[j] != 0)
{
break;
}
}
k = j; // minimum code length
if (l < j)
{
l = j;
}
for (i = BMAX; i != 0; i--)
{
if (c[i] != 0)
{
break;
}
}
g = i; // maximum code length
if (l > i)
{
l = i;
}
m[0] = l;
// Adjust last length count to fill out codes, if needed
for (y = 1 << j; j < i; j++, y <<= 1)
{
if ((y -= c[j]) < 0)
{
return(Z_DATA_ERROR);
}
}
if ((y -= c[i]) < 0)
{
return(Z_DATA_ERROR);
}
c[i] += y;
// Generate starting offsets into the value table for each length
x[1] = j = 0;
p = 1;
xp = 2;
while (--i != 0)
{
// note that i == g from above
x[xp] = j += c[p];
xp++;
p++;
}
// Make a table of values in order of bit lengths
i = 0;
p = 0;
do
{
if ((j = b[bindex + p]) != 0)
{
v[x[j]++] = i;
}
p++;
}while (++i < n);
n = x[g]; // set n to length of v
// Generate the Huffman codes and for each, make the table entries
x[0] = i = 0; // first Huffman code is zero
p = 0; // grab values in bit order
h = -1; // no tables yet--level -1
w = -l; // bits decoded == (l * h)
u[0] = 0; // just to keep compilers happy
q = 0; // ditto
z = 0; // ditto
// go through the bit lengths (k already is bits in shortest code)
for (; k <= g; k++)
{
a = c[k];
while (a-- != 0)
{
// here i is the Huffman code of length k bits for value *p make tables up to
// required level
while (k > w + l)
{
h++;
w += l; // previous table always l bits
// compute minimum size table less than or equal to l bits
z = g - w;
z = z > l ? l : z; // table size upper limit
if ((f = 1 << (j = k - w)) > a + 1)
{
// try a k-w bit table too few codes for k-w bit table
f -= a + 1; // deduct codes from patterns left
xp = k;
if (j < z)
{
while (++j < z)
{
// try smaller tables up to z bits
if ((f <<= 1) <= c[++xp])
{
break; // enough codes to use up j bits
}
f -= c[xp]; // else deduct codes from patterns
}
}
}
z = 1 << j; // table entries for j-bit table
// allocate new table
if (hn[0] + z > MANY)
{
// (note: doesn't matter for fixed)
return(Z_DATA_ERROR); // overflow of MANY
}
u[h] = q = hn[0]; // DEBUG
hn[0] += z;
// connect to last table, if there is one
if (h != 0)
{
x[h] = i; // save pattern for backing up
r[0] = (sbyte)j; // bits in this table
r[1] = (sbyte)l; // bits to dump before this table
j = SharedUtils.URShift(i, w - l);
r[2] = q - u[h - 1] - j; // offset to this table
Array.Copy(r, 0, hp, (u[h - 1] + j) * 3, 3); // connect to last table
}
else
{
t[0] = q; // first table is returned result
}
}
// set up table entry in r
r[1] = (sbyte)(k - w);
if (p >= n)
{
r[0] = 128 + 64; // out of values--invalid code
}
else if (v[p] < s)
{
r[0] = (sbyte)(v[p] < 256 ? 0 : 32 + 64); // 256 is end-of-block
r[2] = v[p++]; // simple code is just the value
}
else
{
r[0] = (sbyte)(e[v[p] - s] + 16 + 64); // non-simple--look up in lists
r[2] = d[v[p++] - s];
}
// fill code-like entries with r
f = 1 << (k - w);
for (j = SharedUtils.URShift(i, w); j < z; j += f)
{
Array.Copy(r, 0, hp, (q + j) * 3, 3);
}
// backwards increment the k-bit code i
for (j = 1 << (k - 1); (i & j) != 0; j = SharedUtils.URShift(j, 1))
{
i ^= j;
}
i ^= j;
// backup over finished tables
mask = (1 << w) - 1; // needed on HP, cc -O bug
while ((i & mask) != x[h])
{
h--; // don't need to update q
w -= l;
mask = (1 << w) - 1;
}
}
}
// Return Z_BUF_ERROR if we were given an incomplete table
return(y != 0 && g != 1 ? Z_BUF_ERROR : Z_OK);
}