queue by type?

typedq.c

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>

struct node {
  struct node *onext;
  struct node *cnext;
  int type;
  int value;
};

struct queue {
  struct node *head;
  struct node *tail;
};

static struct node *__node_alloc (int type, int value) {
  struct node *node;

  node = (struct node *) malloc(sizeof(struct node));
  node->onext = NULL;
  node->cnext = NULL;
  node->type = type;
  node->value = value;

  return(node);
}

static void __push (struct queue *queue, struct node *node) {
  struct node *tail;
  node->onext = node;
  node->cnext = NULL;
  if ((tail = queue->tail) != NULL) {
    if (tail->type == node->type) {
      tail->onext->cnext = node;
      tail->onext = node;
    } else {
      tail->onext = node;
      queue->tail = node;
    }
  } else {
    queue->head = node;
    queue->tail = node;
  }
}

static struct node *__pop (struct queue *queue) {
  struct node *head;
  struct node *node;

  if ((head = queue->head) == NULL)
    return(NULL);

  if ((node = head->cnext) != NULL) {
    node->onext = head->onext;
    queue->head = node;
  } else if (head != head->onext) {
    queue->head = head->onext;
  } else {
    queue->head = NULL;
    queue->tail = NULL;
  }

  return(head);
}

static void __dump (struct queue *queue) {
  struct node *p;

  for (p = queue->head; p != NULL; p = p->onext) {
    struct node *q;
    printf("%d: ", p->type);
    for (q = p; q != NULL; q = q->cnext) {
      printf("%d -> ", q->value);
    }
    printf("X\n");

    if (p == p->onext)
      break;
  }
}

int main (int argc, char **argv) {
  struct queue queue;
  struct node *node;
  queue.head = NULL;
  queue.tail = NULL;

  __push(&queue, __node_alloc(10, 0));
  __push(&queue, __node_alloc(10, 1));
  __push(&queue, __node_alloc(20, 1));
  __push(&queue, __node_alloc(20, 2));
  __push(&queue, __node_alloc(20, 3));
  __push(&queue, __node_alloc(10, 4));
  __push(&queue, __node_alloc(30, 5));
  __dump(&queue);
  while ((node = __pop(&queue)) != NULL) {
    printf("POP %d %d\n", node->type, node->value);
  }

  return(0);
}