Adventure Game Studio

this problem is solved

Hello, I know it's not nice to bother other people about his very own algorithm, but the problem I have looks very simple (and it is probably very simple) - But, you know, sometimes you have been trying to find the error for so long that you don't see a very obvious error anymore.

Here is the function :


static ADDR AGSH_Allocator::searchContiguousBlock(ADDR node,  ADDR contiguousToBlock) {
 
    ADDR return_node = node;
 
    AGSH_Console.DebugMsg(String.Format("searchContiguousBlock (%d, %d)", node, contiguousToBlock));

    if (contiguousToBlock < 0) {
      AGSH_Console.DebugMsg(String.Format("Cannot search block contiguous to an invalid node (@%d)", contiguousToBlock));
      return INVALID_ADDR;
    }

    if (node == INVALID_ADDR) {
      //node = INVALID_ADDR;
      //do nothing; return INVALID_ADDR
      AGSH_Console.DebugMsg("null"); //DEBUG
    } else {
 
      int whatSide = AGSH_Allocator.compareNodes(contiguousToBlock, node);

      if (whatSide == CMP_INTERSECT) {
        AGSH_Console.DebugMsg("CMP_INTERSECT"); //DEBUG
        //we are probably in the case where contiguousToblock == node; search 'node's sons
        return_node = AGSH_Allocator.searchContiguousBlock(AGSH_FreeNodesLifo.GetLeftSon(node),  contiguousToBlock);
        if (return_node == INVALID_ADDR)
          return_node = AGSH_Allocator.searchContiguousBlock(AGSH_FreeNodesLifo.GetRightSon(node),  contiguousToBlock);
      } else if (whatSide == CMP_LEFT) {
        AGSH_Console.DebugMsg("CMP_LEFT"); //DEBUG
        return_node = AGSH_Allocator.searchContiguousBlock(AGSH_FreeNodesLifo.GetLeftSon(node), contiguousToBlock);
      } else if (whatSide == CMP_RIGHT) {
        AGSH_Console.DebugMsg("CMP_RIGHT"); //DEBUG
        return_node = AGSH_Allocator.searchContiguousBlock(AGSH_FreeNodesLifo.GetRightSon(node), contiguousToBlock);
      } else if (whatSide == CMP_LEFT_CONTIGUOUS_RIGHT || whatSide == CMP_RIGHT_CONTIGUOUS_LEFT) {   
        //block 'contiguousToBlock' is contiguous to 'node'
        AGSH_Console.DebugMsg("CMP_LEFT_CONTIGUOUS_RIGHT || whatSide == CMP_RIGHT_CONTIGUOUS_LEFT"); //DEBUG
        //do nothing; we return 'node'
      } else {
        AGSH_Console.Error(String.Format("AGSH_Allocator::searchContiguousBlock : Forbidden value : whatSide=%d", whatSide));
      }
    }

    AGSH_Console.DebugMsg(String.Format("Return : %d", node));

    return return_node;
 
  }
}



and here is the output :


searchContiguousBlock (688, 688)
CMP_INTERSECT
searchContiguousBlock (-1, 688)
null
Return : -1
searchContiguousBlock (-1, 688)
null
Return : -1
Return : 688


As you can see, the execution enters the "CMP_INTERSECT" condition and tries searchContiguousBlock on leftSon and rightSon. Both return INVALID_ADDR (-1); But, strangely, the final return is 688 instead of -1...

Why so???

---

Note : i noticed that when i don't use a temporary variable (result_node) to modify the return value directly from a parameter (node), it causes bugs (the function returns random values). That means that if 'node' is a parameter, and if i write "node = ...;" and then "return node;", then the return value will be incorrect.
This has nothing to do with my problem explained above, and someone else probably noticed it before me, but it's quite confusing.

Hmmm.

    AGSH_Console.DebugMsg(String.Format("Return : %d", return_node));

?

return_node is set to node in the beginning and not changed if the node is invalid; so in that case your line displays the correct return value although you've used the wrong variable.

Quote from: KhrisMUC on Tue 10/07/2007 09:23:44

    AGSH_Console.DebugMsg(String.Format("Return : %d", return_node));

?

We found it at the same time. THANK YOU!
Grrr, i always put some "printf" to debug, and finally they are more bugged than the code to debug ;)