優れたring bufferまたはcycle bufferの実装コード

#define CIRCLE_BUFFSIZE 1024 * 1024
#define min(x, y) ((x) < (y) ? (x) : (y))

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 = CIRCLE_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;  
} 
static int uninit_cycle_buffer(void)  
{
     if(!fifo)
         return -1;
     pthread_mutex_destroy(&fifo->lock);
     if(fifo->buf)
         free(fifo->buf);
     free(fifo);
}

unsigned int fifo_get(unsigned char *buf, unsigned int len)  
{  
    unsigned int l;  
    len = min(len, fifo->in - fifo->out);  
    if(len <= 0)
        return 0;

    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;  
}