hash table and fast two sum in C

twoSum.c

typedef struct _node {
    int k;
    int v;
    struct _node * next;
} node;

static int hash (int x, int m){
    return ((x ^ 0x3FB15C87) & ~0x80000000) % m; 
}

void hashins(node **T, int m, int k, int v){
    int h = hash(k, m);
    node *p;
    node *n = malloc(sizeof(node));
    n->k = k;
    n->v = v;
    n->next = NULL;
    if (T[h] == NULL){
        T[h] = n;
    }
    else {
        p = T[h];
        while (1){
            if (p->k == k){
                p->v = v;
                free(n);
                return;
            }
            else if (p->next == NULL){
                p->next = n;
                return;
            }
            p = p->next;
        }
    }
}

int hashsrh(node **T, int m, int k, int *v){
    int h = hash(k, m);
    node *p = T[h];
    if (!p) return -1; // NFOUND
    while (p){
        if (p->k == k){
            *v = p->v;
            return 0;
        }
        p = p->next;
    }
    return -1; //NFOUND
}

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* twoSum(int* nums, int numsSize, int target, int* returnSize){
    node **T = calloc(numsSize, sizeof(node *));
    memset(T, 0, numsSize * sizeof(node*));
    int m = numsSize;
    *returnSize = 2;
    int *r = malloc(2 * sizeof(int));
    
    for (int i = 0; i < numsSize; i ++){
        hashins(T, m, target - nums[i], i);
    }
    for (int i = 0; i < numsSize; i ++){
        int j;
        if (hashsrh(T, m, nums[i], &j) == 0 && i != j){
            r[0] = i; r[1] = j;
            return r;
        }
    }
    return r;
}