void BuildLength(int[] childs)
{
this.length = new byte[freqs.Length];
int numNodes = childs.Length / 2;
int numLeafs = (numNodes + 1) / 2;
int overflow = 0;
for (int i = 0; i < maxLength; i++) {
bl_counts[i] = 0;
}
// First calculate optimal bit lengths
int[] lengths = new int[numNodes];
lengths[numNodes - 1] = 0;
for (int i = numNodes - 1; i >= 0; i--) {
if (childs[2 * i + 1] != -1) {
int bitLength = lengths[i] + 1;
if (bitLength > maxLength) {
bitLength = maxLength;
overflow++;
}
lengths[childs[2 * i]] = lengths[childs[2 * i + 1]] = bitLength;
} else {
// A leaf node
int bitLength = lengths[i];
bl_counts[bitLength - 1]++;
this.length[childs[2 * i]] = (byte)lengths[i];
}
}
// if (DeflaterConstants.DEBUGGING) {
// //Console.WriteLine("Tree "+freqs.Length+" lengths:");
// for (int i=0; i < numLeafs; i++) {
// //Console.WriteLine("Node "+childs[2*i]+" freq: "+freqs[childs[2*i]]
// + " len: "+length[childs[2*i]]);
// }
// }
if (overflow == 0) {
return;
}
int incrBitLen = maxLength - 1;
do {
// Find the first bit length which could increase:
while (bl_counts[--incrBitLen] == 0) {
}
// Move this node one down and remove a corresponding
// number of overflow nodes.
do {
bl_counts[incrBitLen]--;
bl_counts[++incrBitLen]++;
overflow -= 1 << (maxLength - 1 - incrBitLen);
} while (overflow > 0 && incrBitLen < maxLength - 1);
} while (overflow > 0);
/* We may have overshot above. Move some nodes from maxLength to
* maxLength-1 in that case.
*/
bl_counts[maxLength - 1] += overflow;
bl_counts[maxLength - 2] -= overflow;
/* Now recompute all bit lengths, scanning in increasing
* frequency. It is simpler to reconstruct all lengths instead of
* fixing only the wrong ones. This idea is taken from 'ar'
* written by Haruhiko Okumura.
*
* The nodes were inserted with decreasing frequency into the childs
* array.
*/
int nodePtr = 2 * numLeafs;
for (int bits = maxLength; bits != 0; bits--) {
int n = bl_counts[bits - 1];
while (n > 0) {
int childPtr = 2 * childs[nodePtr++];
if (childs[childPtr + 1] == -1) {
// We found another leaf
length[childs[childPtr]] = (byte)bits;
n--;
}
}
}
// if (DeflaterConstants.DEBUGGING) {
// //Console.WriteLine("*** After overflow elimination. ***");
// for (int i=0; i < numLeafs; i++) {
// //Console.WriteLine("Node "+childs[2*i]+" freq: "+freqs[childs[2*i]]
// + " len: "+length[childs[2*i]]);
// }
// }
}
