C language -- ring buffer

How the ring buffer works

Ring buffers are fixed-size buffers,Works like memory is contiguous and loopable.在生成和使用内存时,There is no need to clear all the original data,只要调整head/tail指针即可.当添加数据时,head指针前进.当使用数据时,tail指针向前移动.当到达缓冲区的尾部时,指针又回到缓冲区的起始位置.

优势：When there is a lot of data but you don't need to store it all,Computers process data first,After processing, the data will be released,Proceed to the next one.Then the memory for the processed data will be wasted.因为后来的数据只能往后排队,If the remaining data are moved forward once,Efficiency will be greatly reduced.Hence the circular queue.The core is to apply for a piece of memory,Connect them end to end by a special method,形成一个闭环的内存地址.这样既可以继续处理源源不断的数据,There is no need to apply for new memory space to temporarily store new data,效率大大提高.

劣势：One of the most important features of the ring buffer is the matching between the speed of writing and the speed of reading,环形缓冲区一般是将数据先写入缓冲区内,然后有个写的指针位置,但是不能超过读的位置,Because the data has not been read yet,write data,This will cause the data to be overwritten by new data before it has been read,造成数据的丢失.Reading data is the same principle,The read pointer cannot exceed the write location,这样就会读到之前读过的数据,造成数据的重复.空间如果设置的太大,会造成内存的浪费,有内存一直处于空闲状态,If the space is set too small,可能会造成读的速度快于写的速度,导致读的过程中会有短暂的等待时间,造成效率不是最高.

1、写入数据<缓冲区

 2、写入数据>缓冲区

 代码：

#include "RingBuffer.h" 

static UINT16 validlen;  			    	//已使用的数据长度
static UINT8* pHead = NULL; 				//The first address of the ring buffer
static UINT8* pTail = NULL; 				//Ring buffer end address
static UINT8* pValid = NULL; 				//The first address of the used buffer
static UINT8* pValidTail = NULL; 		    //The end address of the used buffer

//malloc申请空间 
void initRingbuffer(void)
{
	if(pHead == NULL)
	{
		pHead = (char*) malloc(BUFFER_SIZE);
	}
	pValid = pValidTail = pHead;
	pTail = pHead + BUFFER_SIZE;
	validlen = 0;
}

//Free the ring buffer 
void releaseRingbuffer(void)
{
	if(pHead != NULL)
		free(pHead);
	pHead = NULL; 
}

/*************************************************************/
/******功能:Initializes the specified ring buffer			             *****/
/******param:@buffer：Defines the first address of the static buffer array 
       param:@size:The size of this buffer                       ******/
/************************************************************/
void InitRingBuffer(UINT8* buffer, UINT16 size)
{
	if(pHead == NULL)
	{
		pHead = buffer;
	}
	pValid = pValidTail = pHead;
	pTail = pHead + size;
	validlen = 0;
}

/***********************************************************/
/******功能:向缓冲区写入数据			               *****/
/******param:@buffer 写入的数据指针
             @len 写入的数据长度		              ******/
/******return:-1 The length of the data written is too large -2:The buffer is not initialized  *****/
/***********************************************************/
int writeRingbuffer(UINT8* buffer, UINT32 len)
{
	UINT16 len1, len2, movelen;
	if(len > BUFFER_SIZE)
	{
		return -1;
	}
	if(pHead == NULL)
	{
		return -2;
	}
	assert(buffer);
	
	//将要写入的数据copy到pVaildTaill处
	if(pValidTail+len > pTail)
	{	
		len1 = pTail - pValidTail;              //放到尾部 
		len2 = len - len1;                      //The position where the rear can't be put down,从头开始放 
		memcpy(pValidTail, buffer, len1);
		memcpy(pHead, buffer + len1, len2);
		pValidTail = pHead + len2;              //New valid data 
	}else
	{
		memcpy(pValidTail, buffer, len);
		pValidTail += len;                      //End of new valid data area 
	}

	//Recalculate the starting position of the used area
	if(validlen + len > BUFFER_SIZE)
	{
		movelen = validlen + len - BUFFER_SIZE;
		if(pValid + movelen > pTail)            //需要分成两段 
		{
			len1 = pTail - pValid;
			len2 = movelen - len1;
			pValid = pHead + len2;
		}else
		{
			pValid += movelen;
		}
		validlen = BUFFER_SIZE;
	}else
	{
		validlen += len;
	}
	return 0;
}

/*************************************************************/  
/******功能:Reads the specified length of data from the buffer	                 *****/
/******param:@buffer Pointer to receive read data
             @length 读取的数据长度		                ******/
/******return:-1 The buffer is not initialized >0:Valid data size read    *****/
/*************************************************************/
int readRingbuffer(UINT8* buffer, UINT32 len)
{
	UINT16 len1, len2;
	
	if(pHead == NULL)
	{
		return -1;
	}
	assert(buffer);
	if(len > validlen)
	{
		len = validlen;
	}
	if(validlen == 0)
	{
		return 0;
	}
	
	if(pValid + len > pTail)                     //需要分成两段copy 
	{
		len1 = pTail - pValid;
		len2 = len - len1;
		memcpy(buffer, pValid, len1);           //第一段 
		memcpy(buffer + len1, pHead, len2);     //第二段 ,Wrap around to the beginning of the entire store 
		pValid = pHead + len2;                  //Update the start of the used buffer
	}else
	{
		memcpy(buffer, pValid, len);
		pValid += len;                         //Update the start of the used buffer 
	}
	validlen -= len;                           //Update the length of the used buffer 
	return len;
}

/*************************************************************/
/******功能:Get the used buffer data length	                 *****/
/******param:void                                       ******/
/******return:The data length of the used buffer                     *****/
/************************************************************/
UINT32 getRingbufferValidLen(void)
{
	return validlen;
}