mm_free()

void mm_free (void *ptr) {
  size_t payloadSize;
  BlockInfo * blockInfo;
  BlockInfo * followingBlock;
  size_t blockSize;

  blockInfo = (BlockInfo *)ptr; //这里有问题malloc得到的指针是header后面一个，你自己都return 了 POINTER_ADD(ptrFreeBlock,WORD_SIZE);,明显应该是 POINTER_ADD(ptrFreeBlock,WORD_SIZE);
  blockSize = SIZE(blockInfo->sizeAndTags);
   //Set Header
  blockInfo->sizeAndTags &= (~TAG_USED);
  //既然是freeblock，你应该设置完header,再补上footer,原来没有footer，是因为被malloc占用了
  insertFreeBlock(blockInfo);

  followingBlock = (BlockInfo *)POINTER_ADD(blockInfo,blockSize);
  followingBlock->sizeAndTags &= (~TAG_PRECEDING_USED);
  //Calculate Payload Size
  payloadSize = POINTER_SUB(SIZE(blockInfo->sizeAndTags),2*WORD_SIZE); //这个就不用了，因为题目里面的payloadSize,就是你的blockSize

  //Set Footer
  (*(size_t *)(POINTER_ADD(blockInfo,payloadSize))=(blockInfo->sizeAndTags));//
  //以上这个应该改为 
  //(*(size_t *)(POINTER_ADD(blockInfo,blockSize - WORD_SIZE))=(blockInfo->sizeAndTags));//
  PUT(FOOTER(blockInfo),blockInfo->sizeAndTags);//上面已经设置footer了，这个就不用了
  // Implement mm_free.  You can change or remove the declaraions
  // above.  They are included as minor hints.
  //
  //最后，设置完insertFreeBlock后，
  //你就直接coalesceFreeBlock(blockInfo)，把blockInfo邻近的block合并下就好了.

}