The find_fit function uses 3 auxillary helpers:

• GET_SIZE(q) returns the size of a block begining at address q. This address should be the address of the header, NOT the allocated/free part.
• GET_ALLOC(q) returns 1 if the block at address q is allocated and 0 if the block is free.
• NEXT_BLKP(p) returns the beginning address of the allocated/free part of the next block after the block pointed to by p. But (IMPORTANT) the address p should also point to the allocated/free part of the current block, not to its header.

    1   static void *find_fit(size_t size)
    2   {
    3     void *bp;
    4   
    5     /* Find the first free block big enough */
    6     for(bp = heap_listp; GET_SIZE(HDRP(bp)) > 0; bp = NEXT_BLKP(bp)) {
    7       if (!GET_ALLOC(HDRP(bp)) && (asize <= GET_SIZE(HDRP(bp))) ) {
    8         return bp;
    9       }
   10     }
   11     return NULL; // No free block big enough
   12   }
   13