void *Ring_add(T ring, int pos, void *x) {
assert(ring);
assert(pos >= -ring->length && pos<=ring->length+1);
if (pos == 1 || pos == -ring->length)
return Ring_addlo(ring, x);
else if (pos == 0 || pos == ring->length + 1)
return Ring_addhi(ring, x);
else {
struct node *p, *q;
int i = pos < 0 ? pos + ring->length : pos - 1;
{
int n;
q = ring->head;
if (i <= ring->length/2)
for (n = i; n-- > 0; )
q = q->rlink;
else
for (n = ring->length - i; n-- > 0; )
q = q->llink;
}
NEW(p);
{
p->llink = q->llink;
q->llink->rlink = p;
p->rlink = q;
q->llink = p;
}
ring->length++;
return p->value = x;
}
}
void *Ring_addlo(T ring, void *x){
assert(ring);
Ring_addhi(ring, x);
ring->head = ring->head->l_link;
return x;
}
T Ring_ring(void *x, ...) {
va_list ap;
T ring = Ring_new();
va_start(ap, x);
for ( ; x; x = va_arg(ap, void *))
Ring_addhi(ring, x);
va_end(ap);
return ring;
}
void *Ring_add(T ring, int pos, void *x){
assert(ring);
assert(pos >= -ring->length && pos <= ring->length);
if (pos == 1 || pos == -ring->length){
return Ring->addlo(ring, x);
}
else if (pos == 0 || pos == ring->length + 1){
return Ring_addhi(ring, x);
}
else{
struct node *p;
struct node *q;
int i = pos < 0 ? pos + ring->length : pos - 1;
// q <- ith node
{
int n;
q = ring->head;
if (i <= ring->length / 2){
for (n = i; n-- > 0; ){
q = q->r_link;
}
}
else{
for (n = ring->length - i; n-- > 0; ){
q = q->l_link;
}
}
}
NEW(p);
// insert p to the left of q
p->r_link = q;
p->l_link = q->l_link;
q->l_link->r_link = p;
q->l_link = p;
ring->length++;
return p->value = x;
}
}
