/****************************************************************************************************

* buf : 存放数据的缓冲区地址

* size: 缓冲区的大小(必须是2的幂)

* in ：写指针下标

* out ：读指针下标

* 缓冲区模型如下：size固定大小，in的值始终大于等于out的值

* 先从ringbuf->in到缓冲区末端写数据，如果还没写完，再从缓冲区头开始写入剩下的，从而实现了循环缓冲。

* +--------------+(in)-----------------+(size)

* +

* +-----+(out)-------------------------+

* 那么可用的缓冲空间大小就是(size - in + out)

* 所以写数据时

* 1.先从length和(ringbuf->size - ringbuf->in + ringbuf->out)之间取一个较小的值赋给length

* 2.再判断缓冲区的末端(buffer->size - (buffer->in & (buffer->size - 1)))大小是否够保存length的数据给len

* 3.拷贝len长度的数据到缓冲区的末端 memcpy(buffer->buf + (buffer->in & (buffer->size - 1)), data, len);

* 4.再拷贝剩下的数据到缓冲区的前端 memcpy(buffer->buf, data + len, length - len); 如果length - len为0则无操作。

* 5.写指针的下标增加length长度。

* 6.返回实际写入缓冲区的长度。

*

* 读取数据：

* 1.数据量的大小由(buffer->in - buffer->out)决定

* amount和(buffer->in - buffer->out)取小值给amount，作为一次读取的数据大小

* 2.尾部缓冲数据大小由(buffer->size - (buffer->out & (buffer->size - 1)))决定

* 判断尾部数据和总需求数据大小，取小值给len

* 3.先拷贝尾部缓冲的数据到目的memcpy(target, buffer->buf + (buffer->out & (buffer->size - 1)), len);

* 4.再拷贝头部缓冲数据 memcpy(target + len, buffer->buf, amount - len); amount - len为0则无操作。

* 5.读指针的下标增加amount大小

* 6.返回实际读取的数据大小。

* 注意:

* 当(ringbuf->in == ringbuf->out + ringbuf->size)即(ringbuf->in == ringbuf->out + ringbuf->size)时，表示缓冲区已满.

* 此时得到的较小值一定是0，后面实际写入的字节数也全为0。

*

* 既然ringbuf->size是2的幂，那么(ringbuf->size-1)也就是一个除最高位为0，其余二进制位都为1的一个数值

* 也就能保证(ringbuf->in & (ringbuf->size - 1))不会超过(ringbuf->size - 1)，和(ringbuf->in)%(ringbuf->size - 1)的效果一样

* 从上面可以看出，ringbuf->in的值可以从0变化到超过fifo->size的数值，还要注意的是数据类型的翻转问题

* ringbuf->out也如此，但它们的差不会超过ringbuf->size。

****************************************************************************************************/

可参考文件

 

 

typedef struct cycle_buffer { unsigned char* buf;unsigned int size;unsigned int in;unsigned int out;}RingBuffer;RingBuffer *RingBuffer_create(int length);void RingBuffer_destroy(RingBuffer *buffer);int RingBuffer_read(RingBuffer *buffer, char *target, int amount);int RingBuffer_write(RingBuffer *buffer, char *data, int length);int RingBuffer_empty(RingBuffer *buffer);int RingBuffer_Reset(RingBuffer *buffer);

 

#define min(x, y) ((x) < (y) ? (x) : (y))#define ROUND_UP_2(num) (((num)+1)&~1)#define DEFAULT_BUF_SIZE (2*1024*1024)RingBuffer *RingBuffer_create(int length){unsigned int size = ROUND_UP_2(length);if ( (size&(size-1)) || (size < DEFAULT_BUF_SIZE) ){size = DEFAULT_BUF_SIZE;}RingBuffer *buffer = (RingBuffer *)malloc(sizeof(RingBuffer)); if (!buffer) {return NULL; }memset(buffer, 0, sizeof(RingBuffer)); buffer->size = size; buffer->in = 0;buffer->out = 0; buffer->buf = (unsigned char *)malloc(size); if (!buffer->buf){free(buffer);return NULL;}memset(buffer->buf, 0, size);return buffer;}void RingBuffer_destroy(RingBuffer *buffer){if(buffer) {free(buffer->buf);free(buffer);}}int RingBuffer_Reset(RingBuffer *buffer){if (buffer == NULL){return -1;}buffer->in = 0;buffer->out = 0;memset(buffer->buf, 0, buffer->size);return 0;}int RingBuffer_empty(RingBuffer *buffer){return buffer->in == buffer->out;}int RingBuffer_write(RingBuffer *buffer, char *data, int length){unsigned int len = 0;length = min(length, buffer->size - buffer->in + buffer->out); len = min(length, buffer->size - (buffer->in & (buffer->size - 1)));memcpy(buffer->buf + (buffer->in & (buffer->size - 1)), data, len);memcpy(buffer->buf, data + len, length - len);buffer->in += length;return length;}int RingBuffer_read(RingBuffer *buffer, char *target, int amount){unsigned int len = 0;amount = min(amount, buffer->in - buffer->out);len = min(amount, buffer->size - (buffer->out & (buffer->size - 1)));memcpy(target, buffer->buf + (buffer->out & (buffer->size - 1)), len);memcpy(target + len, buffer->buf, amount - len);buffer->out += amount;return amount;}