我有一个小程序，应该计算2位分支预测器成功预测的百分比。我已经完成了所有工作，但我的产量并不是我所预期的，优势停留在91％左右，而不是我认为应该达到98％或99％。我认为问题可能在于如何将掩码应用于地址。有人可以查看我的代码并验证这是否是问题。
程序遍历一个文件，该文件具有gcc编译器运行的分支历史记录，包含大约1792个地址和一个数字列，其中1表示分支，0表示未分支。
static void twoBitPredictor_v1(StreamWriter sw)
{
uint hxZero = 0x000000000;
uint uMask1 = 0x00000000;
int nCorrectPrediction = 0;
uint uSize2;
int nSize;
int nTotalReads;
int nTableMin = 2;
int nTableMax = 16;
int nTaken = 0;
uint[] uArrBt1;
sw.WriteLine("\n\nTwo-Bit Predictor Results Ver. 1\n");
sw.WriteLine("-------------------------\n");
sw.WriteLine("Total" + "\t" + "Correct");
sw.WriteLine("Reads" + "\t" + "Prediction" + "\t" + "Percentage");
System.Console.WriteLine("\n\nTwo-Bit Predictor Results Ver. 1\n");
System.Console.WriteLine("-------------------------\n");
System.Console.WriteLine("Total" + "\t" + "Correct");
System.Console.WriteLine("Reads" + "\t" + "Prediction" + "\t" + "Percentage");
for (int _i = nTableMin; _i <= nTableMax; _i++)
{
StreamReader sr2 = new StreamReader(@"C:\Temp\gccHist.txt");
nSize = _i;
uSize2 = (uint)(Math.Pow(2, nSize));
uArrBt1 = new uint[2 * uSize2];
for (int i = 0; i < uSize2; i++)
uArrBt1[i] = hxZero;
nCorrectPrediction = 0;
nTotalReads = 0;
while (!sr2.EndOfStream)
{
String[] strLineRead = sr2.ReadLine().Split(',');
uint uBRAddress = Convert.ToUInt32(strLineRead[0], 16);
uint bBranchTaken = Convert.ToUInt32(strLineRead[2]);
>>>>> In the line below is where I think lies the problem but not sure how to correct it.
uMask1 = uBRAddress & (0xffffffff >> 32 - nSize);
int _mask = Convert.ToInt32(uMask1);
nTaken = Convert.ToInt32(uArrBt1[2 * _mask]);
switch (Convert.ToInt32(uArrBt1[_mask]))
{
case 0:
if (bBranchTaken == 0) // Branch Not Taken
nCorrectPrediction++;
else
uArrBt1[_mask] = 1;
break;
case 1:
if (bBranchTaken == 0)
{
uArrBt1[_mask] = 0;
nCorrectPrediction++;
}
else
uArrBt1[_mask] = 3;
break;
case 2:
if (bBranchTaken == 0)
{
uArrBt1[_mask] = 3;
nCorrectPrediction++;
}
else
uArrBt1[_mask] = 0;
break;
case 3:
if (bBranchTaken == 0)
uArrBt1[_mask] = 2;
else
nCorrectPrediction++;
break;
}
nTotalReads++;
}
sr2.Close();
double percentage = ((double)nCorrectPrediction / (double)nTotalReads) * 100;
sw.WriteLine(nTotalReads + "\t" + nCorrectPrediction + "\t\t" + Math.Round(percentage, 2) + "%");
System.Console.WriteLine(nTotalReads + "\t" + nCorrectPrediction + "\t\t" + Math.Round(percentage, 2) + "%");
}
}
这是输出：
Two-Bit Predictor Results Ver. 1
-------------------------
Total Correct
Reads Prediction Percentage
1792 997 55.64%
1792 997 55.64%
1792 1520 84.82%
1792 1522 84.93%
1792 1521 84.88%
1792 1639 91.46%
1792 1651 92.13%
1792 1649 92.02%
1792 1649 92.02%
1792 1648 91.96%
1792 1646 91.85%
1792 1646 91.85%
1792 1646 91.85%
1792 1646 91.85%
1792 1646 91.85%