/****************************************************************************
* Function : MakeCodeList
* Description: This function uses a huffman tree to build a list of codes
* and their length for each encoded symbol. This simplifies
* the encoding process. Instead of traversing a tree in
* search of the code for any symbol, the code maybe found
* by accessing codeList[symbol].code.
* Parameters : ht - pointer to root of huffman tree
* codeList - code list to populate.
* Effects : Code values are filled in for symbols in a code list.
* Returned : 0 for success, -1 for failure. errno will be set in the
* event of a failure.
****************************************************************************/
static int MakeCodeList(huffman_node_t *ht, code_list_t *codeList)
{
bit_array_t *code;
byte_t depth = 0;
if((code = BitArrayCreate(EOF_CHAR)) == NULL)
{
perror("Unable to allocate bit array");
return -1;
}
BitArrayClearAll(code);
for(;;)
{
/* follow this branch all the way left */
while (ht->left != NULL)
{
BitArrayShiftLeft(code, 1);
ht = ht->left;
depth++;
}
if (ht->value != COMPOSITE_NODE)
{
/* enter results in list */
codeList[ht->value].codeLen = depth;
codeList[ht->value].code = BitArrayDuplicate(code);
if (codeList[ht->value].code == NULL)
{
perror("Unable to allocate bit array");
BitArrayDestroy(code);
return -1;
}
/* now left justify code */
BitArrayShiftLeft(codeList[ht->value].code, EOF_CHAR - depth);
}
while (ht->parent != NULL)
{
if (ht != ht->parent->right)
{
/* try the parent's right */
BitArraySetBit(code, (EOF_CHAR - 1));
ht = ht->parent->right;
break;
}
else
{
/* parent's right tried, go up one level yet */
depth--;
BitArrayShiftRight(code, 1);
ht = ht->parent;
}
}
if (ht->parent == NULL)
{
/* we're at the top with nowhere to go */
break;
}
}
BitArrayDestroy(code);
return 0;
}
int CHuffmanDecode(struct CHuffman *ch)
{
bit_file_t bfpIn;
int i, newBit;
bfpIn.mode = BF_READ;
bfpIn.buf = ch->inBuf;
bfpIn.bufLen = ch->inLen;
BitFileInit(&bfpIn);
/* open binary output file and bitfile input file */
/* decode input file */
ch->outIndex = 0;
if (!ch->resume) {
BitArrayClearAll(ch->code);
ch->decode_length = 0;
}
while (1) {
newBit = BitFileGetBit(&bfpIn);
if (newBit == EOF) {
fprintf(stderr, "error reading bitfile\n");
exit(1);
}
if (newBit == BUFFER_EMPTY) {
ch->resume = 1;
return BUFFER_EMPTY;
}
if (newBit != 0)
{
BitArraySetBit(ch->code, ch->decode_length);
}
ch->decode_length++;
if (ch->lenIndex[ch->decode_length] != NUM_CHARS)
{
/* there are code of this length */
for(i = ch->lenIndex[ch->decode_length];
(i < NUM_CHARS) && (ch->canonicalList[i].codeLen == ch->decode_length);
i++)
{
if (BitArrayCompare(ch->canonicalList[i].code, ch->code) == 0)
{
/* we just read a symbol output decoded value */
if (ch->canonicalList[i].value == EOF_CHAR) {
if (BitFileByteAlign(&bfpIn)) {
fprintf(stderr, "buffer full\n");
exit(1);
}
}
else {
if (ch->outIndex >= ch->outLen) {
/* buffer limit reached */
fprintf(stderr, "buffer full\n");
exit(1);
}
ch->outBuf[ch->outIndex++] = ch->canonicalList[i].value;
}
BitArrayClearAll(ch->code);
ch->decode_length = 0;
break;
}
}
}
}
ch->resume = 0;
/* close all files */
BitFileClose(&bfpIn);
return 0;
}
