标签：des style class blog code http
/****************************************************************************************************
*
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。
****************************************************************************************************/
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; }
循环缓冲实现（ring buffer/circular buffer),布布扣,bubuko.com
循环缓冲实现（ring buffer/circular buffer)
标签：des style class blog code http
原文地址：http://www.cnblogs.com/eric-geoffrey/p/3772779.html
