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fixed deterministic sort in the huffman tree generation

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This commit is contained in:
Magnus Auvinen 2008-09-23 10:20:07 +00:00
parent 6874cc5bfa
commit 0e0972c538
1 changed files with 28 additions and 14 deletions
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42
src/engine/e_huffman.c
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@ -1,4 +1,3 @@
#include <stdlib.h> /* qsort */
#include <memory.h> /* memset */
#include "e_huffman.h"
@ -8,15 +7,6 @@ typedef struct HUFFMAN_CONSTRUCT_NODE
int frequency;
} HUFFMAN_CONSTRUCT_NODE;
static int sort_func(const void *a, const void *b)
{
if((*(HUFFMAN_CONSTRUCT_NODE **)a)->frequency > (*(HUFFMAN_CONSTRUCT_NODE **)b)->frequency)
return -1;
if((*(HUFFMAN_CONSTRUCT_NODE **)a)->frequency < (*(HUFFMAN_CONSTRUCT_NODE **)b)->frequency)
return 1;
return 0;
}
static void huffman_setbits_r(HUFFMAN_STATE *huff, HUFFMAN_NODE *node, int bits, int depth)
{
if(node->leafs[1] != 0xffff)
@ -31,10 +21,32 @@ static void huffman_setbits_r(HUFFMAN_STATE *huff, HUFFMAN_NODE *node, int bits,
}
}
/* TODO: this should be something faster, but it's enough for now */
void bubblesort(HUFFMAN_CONSTRUCT_NODE **list, int size)
{
int i, changed = 1;
HUFFMAN_CONSTRUCT_NODE *temp;
while(changed)
{
changed = 0;
for(i = 0; i < size-1; i++)
{
if(list[i]->frequency < list[i+1]->frequency)
{
temp = list[i];
list[i] = list[i+1];
list[i+1] = temp;
changed = 1;
}
}
}
}
static void huffman_construct_tree(HUFFMAN_STATE *huff, const unsigned *frequencies)
{
HUFFMAN_CONSTRUCT_NODE nodes_left_storage[HUFFMAN_MAX_NODES];
HUFFMAN_CONSTRUCT_NODE *nodes_left[HUFFMAN_MAX_NODES];
HUFFMAN_CONSTRUCT_NODE nodes_left_storage[HUFFMAN_MAX_SYMBOLS];
HUFFMAN_CONSTRUCT_NODE *nodes_left[HUFFMAN_MAX_SYMBOLS];
int num_nodes_left = HUFFMAN_MAX_SYMBOLS;
int i;
@ -52,20 +64,22 @@ static void huffman_construct_tree(HUFFMAN_STATE *huff, const unsigned *frequenc
nodes_left_storage[i].frequency = frequencies[i];
nodes_left_storage[i].node_id = i;
nodes_left[i] = &nodes_left_storage[i];
}
}
huff->num_nodes = HUFFMAN_MAX_SYMBOLS;
/* construct the table */
while(num_nodes_left > 1)
{
qsort(nodes_left, num_nodes_left, sizeof(HUFFMAN_CONSTRUCT_NODE *), sort_func);
/* we can't rely on stdlib's qsort for this, it can generate different results on different implementations */
bubblesort(nodes_left, num_nodes_left);
huff->nodes[huff->num_nodes].num_bits = 0;
huff->nodes[huff->num_nodes].leafs[0] = nodes_left[num_nodes_left-1]->node_id;
huff->nodes[huff->num_nodes].leafs[1] = nodes_left[num_nodes_left-2]->node_id;
nodes_left[num_nodes_left-2]->node_id = huff->num_nodes;
nodes_left[num_nodes_left-2]->frequency = nodes_left[num_nodes_left-1]->frequency + nodes_left[num_nodes_left-2]->frequency;
huff->num_nodes++;
num_nodes_left--;
}