#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void *pointer;
void *move_to_end(void *ptr){
    void *ptr_to_be_moved;
    short int size=*(short int*)ptr;
    ptr_to_be_moved=ptr;
    ptr_to_be_moved=(char*)ptr_to_be_moved+size;
    return ptr_to_be_moved;}

int invalid_pointer(void *ptr){
    void *p,*end;
    int res=0;
    p=pointer;
    end=move_to_end(end);
    p=(short int*)p+1;
    while(p!=end){
        if(p==ptr)res=1;
        p=(char *)p+*(short int*)p;
    }
    return res;

}
void merge(void *ptr){
    void *end_pointer;
    short int shift,tmp,shift2;
    ptr=pointer;
    ptr=(short int*)ptr+1;

    end_pointer=move_to_end(pointer);
    while(ptr!=end_pointer){
    //  printf("mam hlavicku na adrese %p s hodnotou %d\n",ptr,(*(short int*)ptr));
        shift=*(short int*)ptr;
        shift2=*(short int*)((char*)ptr+shift+2);
        if(shift%2==0 && shift2%2==0){
    //      printf("JE MOZNE SPOJIT \n");
            ptr=(char*)ptr+shift+2;
            tmp=*(short int*)ptr;
            ptr=(char*)ptr-shift-2;
            *(short int*)ptr=shift+2+tmp;
            shift=*(short int*)ptr;

        }
//      else printf("neni co spojit \n");
        if(shift%2==0)ptr=(char*)ptr+shift+2;
        else ptr=(char*)ptr+shift+1;
    }

    }




void memory_init(void *ptr, unsigned int size){
    pointer=ptr; //priradim na pointeru ukazovatel na prve "slovo"v pamati
    (*(short int*)ptr)=size; //ulozim do neho vyhradenu velkost
    ptr=(short int*)ptr+1;
    (*(short int*)ptr)=size-4; //oznacim si dalsie nasledujuce slovo nulou

}
void *memory_alloc(unsigned int size){

    void *temp_ptr;
    void *end_ptr;
    //bool even_odd=0;
    short int temp_var,initial_size,msize_counter,swap,header_size;
    end_ptr=pointer;
    end_ptr=move_to_end(end_ptr);

    temp_ptr=pointer;
    initial_size=(*(short int*)temp_ptr);       //ulozim si celkovy pocet
    temp_ptr=(short int *)temp_ptr+1;           //posuniem sa dalej teraz ukazujem na prvu velkost v pamati ....

    while((temp_var=(*(short int*)temp_ptr))%2==1 || temp_var<size ){
            //  if((temp_var%2)!=0)printf("nasiel som plne s velkostou hlavicky %d na adrese %p hladam dalej\n",(*(short int*)temp_ptr),temp_ptr);
                if(temp_var%2==0)temp_ptr=(char *)temp_ptr+temp_var+2;
                else temp_ptr=(char *)temp_ptr+temp_var+1;
    }                                           //mam spravenu podmienku ze to prejde az kym nenajde first fit ked nenajde vrati null a koncime

    //printf("nasiel som volne miesto %d miest ",(*(short int*)temp_ptr));
    //printf("%p ktore sa nachadza na adrese \n",(char*)temp_ptr);

//  if(((char*)temp_ptr+size)>end_ptr){printf("nedostatok miesta v pamati funkcia vracia NULL\n");return NULL;}
        if(size%2!=0)size++;                    //zaukruhlim pokial pride neparne


        if(size==temp_var){                 //pokial sa mi presne hodi do bloku len prepisem header
            size++;
            *(short int*)temp_ptr=size;         //porobim si novu hlavicku
            temp_ptr=(short int *)temp_ptr+1;   //posuniem sa na prvy prok novo alokovanej pamate
    //      printf("%p ktore sa nachadza na adrese \n",(char*)temp_ptr);
    //      printf("%p a ktore konci na adrese \n",(char*)temp_ptr+size-1);
            return temp_ptr;                    //vratim pointer na ten novy blok
            }

        if(size<temp_var){                  //pokial mi presne nefitne do bloku
            size++;
            swap=*(short int*)temp_ptr;
            *(short int*)temp_ptr=size;
    //      printf("%p tu davam novu hlavicku\n",temp_ptr);
            temp_ptr=(char*)temp_ptr+size+1;
    //      printf("%p tu sa presuvam koli novej hlavicke\n",temp_ptr);//posuniem sa na to kde mam novy head zapisat
            *(short int*)temp_ptr=swap-size-1;
    //      printf(" ktora ukazuje na %p\n",(char*)temp_ptr+swap-size+1);
            if((*(short int*)temp_ptr%2)==1) *(short int*)temp_ptr=*(short int*)temp_ptr-1;
            temp_ptr=(char *)temp_ptr-size-1;
            temp_ptr=(short int*)temp_ptr+1;
        //  printf("%p tu sa presuvam na novo alokovanu pamat\n",temp_ptr);
            return temp_ptr;
            }







    //}


    return 0;
}
void memory_free(void *ptr){
    int i_p;
    i_p=invalid_pointer(ptr);
    ptr=(short int*)ptr-1;
    if(i_p==0){
        printf("Invalid Pointer!\n");
        exit(1);
    }
//      printf("povodna hodnota v hlavicke bola %d\n",(*(short int*)ptr));
    (*(short int*)ptr)--;
//  printf("menim hlavicku na adrese %p na hodnotu %d\n",ptr,(*(short int*)ptr));
    merge(pointer);//oznacim header ako prazdny





}





int main (){
    char region[50];
     memory_init(region, 50);

     char* pointer=(char*)memory_alloc(10);

    if (pointer)
    memset(pointer, 0, 10);
    if (pointer)
    memory_free(pointer);

    pointer=(char*)memory_alloc(10);
    pointer=(char*)memory_alloc(15);

    if (pointer)
    memset(pointer, 0, 15);
    if (pointer)
    memory_free(pointer);






return 0;}