Wsrtjtyk

i had to write my own free & malloc function.
So far I have not had a problem with that, but now I am supposed to merge neighboring free memory blocks in the halde_free() function. I would be really grateful if you could help me there.

    #include "halde.h"

#include <stdlib.h>

#include <string.h>

#include <errno.h>

#include <stdio.h>

#include <stdint.h>



/// Magic value for occupied memory chunks.

#define MAGIC ((void*)0xbaadf00d)



/// Size of the heap (in bytes).

#define SIZE (1024*1024*1)



/// Memory-chunk structure.

struct mblock {

    struct mblock *next;

    size_t size;

    char memory;

};



/// Heap-memory area.

char memory[SIZE];



/// Pointer to the first element of the free-memory list.

static struct mblock *head;



/// Helper function to visualise the current state of the free-memory list.

void halde_print(void) {

    struct mblock* lauf = head;



    // Empty list

    if ( head == NULL ) {

        fprintf(stderr, "(empty)n");

        return;

    }



    // Print each element in the list

    while ( lauf ) {

        fprintf(stderr, "(addr: 0x%08zx, off: %7zu, ", (uintptr_t) lauf, (uintptr_t)lauf - (uintptr_t)memory);

        fflush(stderr);

        fprintf(stderr, "size: %7zu)", lauf->size);

        fflush(stderr);



        if ( lauf->next != NULL ) {

            fprintf(stderr, "  -->  ");

            fflush(stderr);

        }

        lauf = lauf->next;

    }

    fprintf(stderr, "n");

    fflush(stderr);

}



void *halde_malloc (size_t size) {

    static int initialized = 0;



    if(initialized == 0){

        head = (struct mblock *) memory;

        head->size = sizeof(memory) - sizeof (struct mblock);

        head->next = NULL;

        initialized = 1;

    }



    if(size == 0){

        return NULL;

    }



    struct mblock *lauf = head;

    struct mblock **prev_next = &head;



    while (lauf != NULL && lauf->size < size){

        prev_next = &(lauf->next);

        lauf = *prev_next;

    }



    if(lauf == NULL){

        errno = ENOMEM;

        return NULL;

    }



    if((lauf->size -size) <= sizeof(struct mblock)){

        *prev_next = lauf->next;

    } else {

        //mblock anlegen und init.

        struct mblock* neu = (struct mblock*) (lauf->memory + size);

        neu->size = lauf->size - sizeof(struct mblock) - size;

        neu->next = lauf->next;



        //mblock anpassen

        lauf->size = size;



        //verketten wiederherstellen

        *prev_next = neu;

    }



    lauf->next = MAGIC;



    return lauf->memory;

}



void halde_free (void *ptr) {

    if(ptr == NULL){

        return;

    }



    struct mblock *mbp = (struct mblock *) ptr - 1;

    if(mbp->next != MAGIC){

        abort();

    } else {

        mbp->next = head;

        head = mbp;

    }

}

The code works so far but i have really no idea how to merge blocks..
The memory management runs over a simply linked lists. The variable head points to the first free memory block.

My idea is to merge the blocks directly in the else part but i don't have a good idea to do that..