JUCE_FIFO实现分析

JUCE_FIFO代码简单剖析，此处的剖析就是给自己留一个方便查询的内容；不做太多内容的要求，只做简单的记录；本文以初学者的角度来些，大牛请飘过O(∩_∩)O

FIFO的功能在博客的其他帖子里面已经有说明了，这里就简单通过图表说明下类里面的两个函数的实现机制，以及使用方法。下面写贴出代码和例子

 1 void AbstractFifo::prepareToWrite (int numToWrite, int& startIndex1,
 2  int& blockSize1, int& startIndex2, int& blockSize2) const noexcept
 3 {
 4  const int vs = validStart.get();
 5  const int ve = validEnd.value;
 6  const int freeSpace = ve >= vs ? (bufferSize - (ve - vs)) : (vs - ve);
 7  numToWrite = jmin (numToWrite, freeSpace - 1);
 8  if (numToWrite <= 0)
 9  {
10  startIndex1 = 0;
11  startIndex2 = 0;
12  blockSize1 = 0;
13  blockSize2 = 0;
14  }
15  else
16  {
17  startIndex1 = ve;
18  startIndex2 = 0;
19  blockSize1 = jmin (bufferSize - ve, numToWrite);
20  numToWrite -= blockSize1;
21  blockSize2 = numToWrite <= 0 ? 0 : jmin (numToWrite, vs);
22  }
23 }
24  
25 
26 void AbstractFifo::prepareToRead (int numWanted, int& startIndex1, int& blockSize1, 
27 int& startIndex2, int& blockSize2) const noexcept
28 {
29  const int vs = validStart.value;
30  const int ve = validEnd.get();
31  const int numReady = ve >= vs ? (ve - vs) : (bufferSize - (vs - ve));
32  numWanted = jmin (numWanted, numReady);
33  if (numWanted <= 0)
34  {
35  startIndex1 = 0;
36  startIndex2 = 0;
37  blockSize1 = 0;
38  blockSize2 = 0;
39  }
40  else
41  {
42  startIndex1 = vs;
43  startIndex2 = 0;
44  blockSize1 = jmin (bufferSize - vs, numWanted);
45  numWanted -= blockSize1;
46  blockSize2 = numWanted <= 0 ? 0 : jmin (numWanted, ve);
47  }
48 }

以上是程序具体实现，下面贴出代码例子;

 1 e.g.
 2  @code
 3  class MyFifo
 4  {
 5  public:
 6  MyFifo() : abstractFifo (1024)
 7  {
 8  }
 9  void addToFifo (const int* someData, int numItems)
10  {
11  int start1, size1, start2, size2;
12  abstractFifo.prepareToWrite (numItems, start1, size1, start2, size2);
13  if (size1 > 0)
14  copySomeData (myBuffer + start1, someData, size1);
15  if (size2 > 0)
16  copySomeData (myBuffer + start2, someData + size1, size2);
17  abstractFifo.finishedWrite (size1 + size2);
18  }
19  void readFromFifo (int* someData, int numItems)
20  {
21  int start1, size1, start2, size2;
22  abstractFifo.prepareToRead (numSamples, start1, size1, start2, size2);
23  if (size1 > 0)
24  copySomeData (someData, myBuffer + start1, size1);
25  if (size2 > 0)
26  copySomeData (someData + size1, myBuffer + start2, size2);
27  abstractFifo.finishedRead (size1 + size2);
28  }
29  private:
30  AbstractFifo abstractFifo;
31  int myBuffer [1024];
32  };
33  @endcode
34 */

其实在这我不想说的太多，主要是刚开始看代码和我自己的想法不太一致，后来详细看了下其实也很简单，就是一个循环队列的实现；使用开始和技术指针确定写入、读取位置提供给外部使用，外部程序无需再自己处理写入、读取位置的判断。就一下两种可能性，一个是开始位置在前结束位置在后，一个是开始位置在后结束位置在前；