Function HuffmanTree_makeFromLengths2

samples/shared/lodepng.cpp:604–641

Second step for the ...makeFromLengths and ...makeFromFrequencies functions. numcodes, lengths and maxbitlen must already be filled in correctly. return value is error. */

value is error.
*/
static unsigned HuffmanTree_makeFromLengths2(HuffmanTree* tree)
{
  uivector blcount;
  uivector nextcode;
  unsigned bits, n, error = 0;

  uivector_init(&blcount);
  uivector_init(&nextcode);

  tree->tree1d = (unsigned*)lodepng_malloc(tree->numcodes * sizeof(unsigned));
  if(!tree->tree1d) error = 83; /*alloc fail*/

  if(!uivector_resizev(&blcount, tree->maxbitlen + 1, 0)
  || !uivector_resizev(&nextcode, tree->maxbitlen + 1, 0))
    error = 83; /*alloc fail*/

  if(!error)
  {
    /*step 1: count number of instances of each code length*/
    for(bits = 0; bits < tree->numcodes; bits++) blcount.data[tree->lengths[bits]]++;
    /*step 2: generate the nextcode values*/
    for(bits = 1; bits <= tree->maxbitlen; bits++)
    {
      nextcode.data[bits] = (nextcode.data[bits - 1] + blcount.data[bits - 1]) << 1;
    }
    /*step 3: generate all the codes*/
    for(n = 0; n < tree->numcodes; n++)
    {
      if(tree->lengths[n] != 0) tree->tree1d[n] = nextcode.data[tree->lengths[n]]++;
    }
  }

  uivector_cleanup(&blcount);
  uivector_cleanup(&nextcode);

  if(!error) return HuffmanTree_make2DTree(tree);
  else return error;
}

/*
given the code lengths (as stored in the PNG file), generate the tree as defined