C语言环形缓冲fifo实现【转】

（转自：https://blog.csdn.net/humanspider1/article/details/80965513）

#define BUFFSIZE 1024 * 1024 
#define min(x, y) ((x) < (y) ? (x) : (y)) 
 
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER; 
 
struct cycle_buffer { 
    unsigned char *buf; 
    unsigned int size; 
    unsigned int in; 
    unsigned int out; 
    pthread_mutex_t lock; 
}; 
 
static struct cycle_buffer *fifo = NULL; 
 
static int init_cycle_buffer(void) 
{
    int size = BUFFSIZE, ret; 
 
    ret = size & (size - 1); 
    if (ret) 
        return ret;
    fifo = (struct cycle_buffer *) malloc(sizeof(struct cycle_buffer)); 
    if (!fifo) 
        return -1; 
 
    memset(fifo, 0, sizeof(struct cycle_buffer)); 
    fifo->size = size; 
    fifo->in = fifo->out = 0; 
    pthread_mutex_init(&fifo->lock, NULL); 
    fifo->buf = (unsigned char *) malloc(size); 
    if (!fifo->buf)
        free(fifo);
    else
        memset(fifo->buf, 0, size); 
    return 0; 
} 
 
unsigned int fifo_get(unsigned char *buf, unsigned int len) 
{ 
    unsigned int l; 
    len = min(len, fifo->in - fifo->out); 
    l = min(len, fifo->size - (fifo->out & (fifo->size - 1))); 
    memcpy(buf, fifo->buf + (fifo->out & (fifo->size - 1)), l); 
    memcpy(buf + l, fifo->buf, len - l); 
    fifo->out += len; 
    return len; 
} 
 
unsigned int fifo_put(unsigned char *buf, unsigned int len) 
{ 
    unsigned int l; 
    len = min(len, fifo->size - fifo->in + fifo->out); 
    l = min(len, fifo->size - (fifo->in & (fifo->size - 1))); 
    memcpy(fifo->buf + (fifo->in & (fifo->size - 1)), buf, l); 
    memcpy(fifo->buf, buf + l, len - l); 
    fifo->in += len; 
    return len; 
}