C汎用プログラミングによる高速レイアウト

# include <stdio.h>
# include <stdlib.h>
# include <string>
# define X[i] (char *)X+size*(i)

int size;

void swap (void *a, void *b) {
        char t[size];
        memcpy (t, a, size);
        memcpy (a, b, size);
        memcpy (b, t, size);
        return;
}

typedef struct pair {
        int left;
        int right;
};

int cpr(void *a, void *b) {
        pair *A = (pair*)a;
        pair *B = (pair*)b;
        return A->right - B->right;
}

typedef int (*compare)(void *a, void *b);

int partition (void *A, int p, int r, compare c) {
        int q = p;
        for (int i = p + 1; i <= r; ++ i) {
                void *x = (char *)A + size * i;
                //void *x = (char *)A[i];
                void *y = (char *)A + size * p;
                if (c(x, y) < 0){
                        ++ q;
                        void *z = (char *)A + size * q;
                        swap (x,z);
                }
        }
        void *z = (char *)A + size * q;
        void *x = (char *)A + size * p;
        swap(z, x);
        return q;
        
}

void qsort(void *A, int p, int r, compare c) {
        while (p < r) {
                int q = partition(A, p, r,c);
                qsort (A, p, q - 1, c);
                p = q + 1;
        }
}

int main () {
        size = sizeof(pair);
        pair A[10];
        srand (time(NULL));
        for (int i = 0; i < 10; ++ i) {
                A[i].left = rand() % 90 + 10;
                A[i].right = rand() % 90 + 10;
        }
        A[0].left = 5;
        A[0].right = 5;
        qsort (A, 0, 9, cpr);
        for (int i = 0; i < 10; ++ i) {
                printf ("%d  ", A[i].left);
        }
        printf ("
");
        for (int i = 0; i < 10; ++ i) {
                printf ("%d  ", A[i].right);
        }
        printf ("
");
        system("pause");
        return 0;
}