/* ===========================================================================
* Construct one Huffman tree and assigns the code bit strings and lengths.
* Update the total bit length for the current block.
* IN assertion: the field freq is set for all tree elements.
* OUT assertions: the fields len and code are set to the optimal bit length
* and corresponding code. The length opt_len is updated; static_len is
* also updated if stree is not null. The field max_code is set.
*/
void build_tree(tree_desc near *desc)
//tree_desc near *desc; /* the tree descriptor */
{
ct_data near *tree = desc->dyn_tree;
ct_data near *stree = desc->static_tree;
int elems = desc->elems;
int n, m; /* iterate over heap elements */
int max_code = -1; /* largest code with non zero frequency */
int node = elems; /* next internal node of the tree */
/* Construct the initial heap, with least frequent element in
* heap[SMALLEST]. The sons of heap[n] are heap[2*n] and heap[2*n+1].
* heap[0] is not used.
*/
heap_len = 0, heap_max = HEAP_SIZE;
for (n = 0; n < elems; n++) {
if (tree[n].Freq != 0) {
heap[++heap_len] = max_code = n;
depth[n] = 0;
} else {
tree[n].Len = 0;
}
}
/* The pkzip format requires that at least one distance code exists,
* and that at least one bit should be sent even if there is only one
* possible code. So to avoid special checks later on we force at least
* two codes of non zero frequency.
*/
while (heap_len < 2) {
int new_ = heap[++heap_len] = (max_code < 2 ? ++max_code : 0);
tree[new_].Freq = 1;
depth[new_] = 0;
opt_len--; if (stree) static_len -= stree[new_].Len;
/* new is 0 or 1 so it does not have extra bits */
}
desc->max_code = max_code;
/* The elements heap[heap_len/2+1 .. heap_len] are leaves of the tree,
* establish sub-heaps of increasing lengths:
*/
for (n = heap_len/2; n >= 1; n--) pqdownheap(tree, n);
/* Construct the Huffman tree by repeatedly combining the least two
* frequent nodes.
*/
do {
pqremove(tree, n); /* n = node of least frequency */
m = heap[SMALLEST]; /* m = node of next least frequency */
heap[--heap_max] = n; /* keep the nodes sorted by frequency */
heap[--heap_max] = m;
/* Create a new node father of n and m */
tree[node].Freq = (u16)(tree[n].Freq + tree[m].Freq);
depth[node] = (u8) (max(depth[n], depth[m]) + 1);
tree[n].Dad = tree[m].Dad = (u16)node;
/* and insert the new node in the heap */
heap[SMALLEST] = node++;
pqdownheap(tree, SMALLEST);
} while (heap_len >= 2);
heap[--heap_max] = heap[SMALLEST];
/* At this point, the fields freq and dad are set. We can now
* generate the bit lengths.
*/
gen_bitlen((tree_desc near *)desc);
/* The field len is now set, we can generate the bit codes */
gen_codes ((ct_data near *)tree, max_code);
}
static void build_tree(
z_stream& s,
tree_desc* desc )
{
ct_data* tree = desc->dyn_tree;
const ct_data* stree = desc->stat_desc->static_tree;
int elems = desc->stat_desc->elems;
int max_code = -1;
int n, m;
int node;
s.heap_len = 0, s.heap_max = HEAP_SIZE;
for( n = 0 ; n < elems ; n++ )
{
if( tree[ n ].Freq )
{
s.heap[ ++s.heap_len ] = max_code = n;
s.depth[ n ] = 0;
}
else
{
tree[ n ].Len = 0;
}
}
while( s.heap_len < 2 )
{
node = s.heap[ ++s.heap_len ] = ( max_code < 2 ? ++max_code : 0 );
tree[ node ].Freq = 1;
s.depth[ node ] = 0;
s.opt_len--;
if( stree )
s.static_len -= stree[ node ].Len;
}
desc->max_code = max_code;
for( n = s.heap_len / 2 ; n >= 1 ; n-- )
pqdownheap( s, tree, n );
node = elems;
do
{
pqremove( s, tree, n );
m = s.heap[ SMALLEST ];
s.heap[ --s.heap_max ] = n;
s.heap[ --s.heap_max ] = m;
tree[ node ].Freq = tree[ n ].Freq + tree[ m ].Freq;
s.depth[ node ] = (unsigned char) ( ( s.depth[ n ] >= s.depth[ m ] ? s.depth[ n ] : s.depth[ m ] ) + 1 );
tree[ n ].Dad = tree[ m ].Dad = (unsigned short) node;
s.heap[ SMALLEST ] = node++;
pqdownheap( s, tree, SMALLEST );
}
while( s.heap_len >= 2 );
s.heap[ --s.heap_max ] = s.heap[ SMALLEST ];
gen_bitlen( s, (tree_desc*) desc );
gen_codes( (ct_data*) tree, max_code, s.bl_count );
}
