循环队列算法实现

循环队列的特点什么的网上资料多,这里就直接上代码吧.
 
1 声明及定义

typedef struct
{
    size_t size;                       /* 初始化后放入队列的容量 */

    volatile unsigned int front;
    volatile unsigned int rear;
}circularqueuehead_t;

typedef struct __attribute__((packed))
{
    unsigned char content[LENGTH];     /* 队列元素的内容 */
}atom_t;

static circularqueuehead_t *g_cq_head; /* 初始化后指向队列头 */
static atom_t              *g_cq;      /* 初始化后指向队列本身 */

2 算法-1

/************************************************
 * Name        : cq_write/cq_read
 * Description :
 * Parameters  : atom_t *operand
 * Retrun      : 0. write/read success
 *               1. write - queue is full
 *                  read  - queue is empty
 * Developer   : zhonghaohua
 * Created     : Wed Oct 30 10:59:46 2013
************************************************/
int cq_write( atom_t *srt)
{
    unsigned int nextpost = ( g_cq_head->front + 1) % g_cq_head->size;

    if( nextpost != g_cq_head->rear ) {
        g_cq[nextpost] = *srt;
        g_cq_head->front = nextpost;

        return 0;
    }
    else {
        return 1;
    }
}

int cq_read( atom_t *srt)
{
    if( g_cq_head->rear != g_cq_head->front) {
        g_cq_head->rear = (g_cq_head->rear + 1) % g_cq_head->size;
        *srt = g_cq[g_cq_head->rear];

        return 0;
    }
    else {
        return 1;
    }
}

3 算法-2

/************************************************
 * Name        : cq_write/cq_read
 * Description :
 * Parameters  : atom_t *operand
 * Retrun      : 0. write/read success
 *               1. write - queue is full
 *                  read  - queue is empty
 * Developer   : zhonghaohua
 * Created     : Wed Oct 30 10:59:46 2013
************************************************/
int cq_write( atom_t *sa)
{
    unsigned int nextpost = ( g_cq_head->front + 1) % g_cq_head->size;

    if( nextpost != g_cq_head->rear ) {
        g_cq[g_cq_head->front] = *sa;
        g_cq_head->front = nextpost;

        return 0;
    }
    else {
        return 1;
    }
}

int cq_read( atom_t *sa)
{
    if( g_cq_head->rear != g_cq_head->front) {
        *sa = g_cq[g_cq_head->rear];
        g_cq_head->rear = (g_cq_head->rear + 1) % g_cq_head->size;

        return 0;
    }
    else {
        return 1;
    }
}

4 说明
    算法-1 和 算法-2 差别不大
    相同:  1) 都以 front + 1 == rear 作为队列满的标记
           2) 都以 rear == front 作为队列空的标记
    差别:  1) 算法-1: write 先[front + 1] = *src,后(front++);  read 先(rear++),      后 *src = [rear].
           2) 算法-2: write 先[front] = *src,    后(front++);  read 先 *src = [rear],后(rear++).
    在front/rear都初始化为0时, 算法-1在第一次读写时, 队列[0]会被跳过.

END.