ciao a tutti devo moltiplicare due interi di lunghezza variabile

codice:
#include <stdio.h> 
#include <stdlib.h> 
#include<time.h> 

int getlength(char *list) 
{ 
    int i=0; 
    while(list[i]!='\0') i++; 
    return i; 
} 

int getlength2(int *list) 
{ 
    int i=0; 
    while(list[i]!=-1) i++; 
    return i; 
} 

int *loadlist(char *list) 
{ 
    int n=getlength(list),i; 
    int *num=(int *)malloc((n+1)*sizeof(int)); 
    char tmp; 

    for(i=0; i<n; i++) { 
        tmp=list[i]; 
        num[n-1-i]=atoi(&tmp); 
    } 
    num[n]=-1; 
    return num; 
} 

void print(int *res, int i) 
{ 
    if(res[i]!=-1) { 
        print(res,i+1); 
        if (i!=0) printf("%d",res[i]); 
        else printf("%d\n",res[i]);     
    } 
} 

int max(int x, int y) 
{ 
    if(x>=y) return x; 
    else return y; 
} 


int *add(int *num1, int *num2) 
{ 
    int n=max(getlength2(num1),getlength2(num2))+100000; 
    int *res=(int *)malloc((n+10000)*sizeof(int)); 
    int tmp,rest=0,i=0; 

    while(num1[i]!=-1 && num2[i]!=-1) 
    { 
        tmp=(num1[i]+num2[i]+rest); 
        res[i]=tmp%10; 
        rest=tmp/10; 
        i++; 
    }     
    if(num1[i]!=-1) { 
         while(num1[i]!=-1) 
         { 
            tmp=(num1[i]+rest); 
            res[i]=tmp%10; 
            rest=tmp/10; 
            i++; 
        } 
    } else if (num2[i]!=-1) 
      { 
        while(num2[i]!=-1) 
        { 
            tmp=(num2[i]+rest); 
            res[i]=tmp%10; 
            rest=tmp/10; 
            i++; 
        } 
    } 
    if(rest!=0) res[i++]=rest; 
    res[i]=-1; 

    return res; 
} 

int *mult(int *num1, int *num2) 
{ 
   int n=max(getlength2(num1),getlength2(num2))+100000; 
   int *res=(int *)malloc((n+1000000)*sizeof(int)); 
   
   int i = 0; 
   for(i = 0; i < *num2; i++) 
   { 
      res = add(res, num1); 
   } 
   return res; 
} 


int main(int argc, const char *argv[]) 
{ 
    clock_t start, end; 
    int *num1, *num2, *res; 
    if(argc!=3) 
    { 
        printf("Usage: add <integer 1> <integer 2>\n"); 
        return 1; 
    } 
    start=clock(); 
    num1=loadlist((char *)argv[1]); 
    num2=loadlist((char *)argv[2]); 
    res=add(num1,num2); 
    res=mult(num1,num2); 
    end=clock(); 
    printf("%g\n",(double)(end-start)/(double)CLOCKS_PER_SEC); 
    print(res,0); 
    return 0; 
}
nella funzione mult le righe per l'allocazione di memoria possono andare bene cosi perche mi segnala un errore di segmentation fault

int n=max(getlength2(num1),getlength2(num2))+1;
int *res=(int *)malloc((n+n)*sizeof(int));