Merge Sort (Optimised)

#include <limits.h>
#include "sort.hpp"
void mergeopt(int* a,int la,int lb);
void mergeoptSort1(int* p,int l);

int* mem;
int pos = 0;

void mergeoptSort(int* p,int l)
{
    mem = new int[l+2];
    mergeoptSort1(p,l);
}

void mergeoptSort1(int* p,int l)
{
    if(l<=1)
        return;
    if(l<=20)
    {
        inSort(p,l);
        return;
    }
    int q = l>>1;
    mergeoptSort1(p,q);
    mergeoptSort1(p+q,l-q);
    mergeopt(p,q,l-q);
}

inline int* alloc(int l)
{
    int* res = mem + pos;
    pos+=l;
    return res;
}

inline void de_alloc(int l)
{
    pos -= l;
}

void mergeopt(int* a,int la,int lb)
{
    int* a1 = alloc(la+1);
    int* b1 = alloc(lb+1);
    for(int i = 0;i<la;++i)
        a1[i] = a[i];
    int* b = a+la;
    for(int i = 0;i<lb;++i)
        b1[i] = b[i];
    a1[la] = INT_MAX;
    b1[lb] = INT_MAX;
    int p = 0, q = 0;
    int t = la+lb;
    for(int i = 0;i<t;++i)
        if(a1[p]<=b1[q])
            a[i] = a1[p++];
        else
            a[i] = b1[q++];
    de_alloc(la+1);
    de_alloc(lb+1);
}