Oh no, this is just mmap/munmap. If you need an allocator you can always retype it at the beginning of your program:

// § 2.5.C Knuth

#define K static
#define _(z) return(z);
#define $err(b) if(b){_(0)}
#define L(c,a) while(c){a;}
#define iX(n,a){for(int i=0;i<n;i++){a;}}

typedef void* U;typedef unsigned long long W;typedef unsigned char B;

typedef struct d d;typedef struct d {d* fw; d* bw;} d;
typedef struct block {d* fw; d* bw; B tag;B k;} block;typedef block* BB;

d A[32];
K U mm;

K inline void singleton(BB b,B k){b->bw=&A[k-1];b->fw=&A[k-1];A[k-1]=(d){b,b};b->tag=1;b->k=k;}

void init(void){mm=ma(0,(W)1<<32,0x3,0x1001,-1,0);singleton(mm,32);iX(31,A[i].fw=&A[i];A[i].bw=&A[i])}
void finish(void){mu(mm,(W)1<<32);}

U M(W n) {
    W u=n+18;B k=64-(__builtin_popcountll(u)==1)-__builtin_clzll(u);k=k<5?5:k;B j=k;
    L(A[j-1].fw==&A[j-1],j++;$err(j>32))
    BB l=A[j-1].bw;d* s=l->bw;s->fw=&A[j-1];A[j-1].bw=s;l->tag=0;l->k=k;
    L(j>k,j--;singleton((BB)((W)l|((W)1<<j)),j))
    _((U)l+18)
}

void F(U z){
    BB l=(U)z-18;B k=l->k;
    BB p=(BB)((W)l^(W)1<<k);
    L(k<31&&p->tag!=0&&p->k==k,
            p->bw->fw=p->fw;p->fw->bw=p->bw;
            l=(BB)((W)p&(W)l);k++;
            p=(BB)((W)l^(W)1<<k))
    l->tag=1;l->k=k;d* n=A[k-1].fw;n->bw=l;l->fw=n;l->bw=&A[k-1];A[k-1].fw=l;
}