public CBP2Reader()
{
returnAddressStack = new uint[RETURN_ADDRESS_STACK_SIZE];
branchesMemory = new CBP2ReaderBranch[BRANCH_MEMORY_NUMBER_OF_LINES][];
for (int i = 0; i < BRANCH_MEMORY_NUMBER_OF_LINES; i++)
{
branchesMemory[i] = new CBP2ReaderBranch[BRANCH_MEMORY_ASSOCIATIVITY_SIZE];
for (int j = 0; j < BRANCH_MEMORY_ASSOCIATIVITY_SIZE; j++)
{
branchesMemory[i][j] = new CBP2ReaderBranch();
}
}
classMisspredicted = new int[8];
branch = new CBP2Branch();
lastBranch = new CBP2Branch();
lastReaderBranch = new CBP2ReaderBranch();
}
public IBranch getNextBranch()
{
int inputByte = bzip2InputStream.ReadByte();
if (inputByte < 0)
{
return(null);
}
branch.branchInfo.branchFlags = 0;
// pass along instruction counts unchanged (we don't care)
if (inputByte == 0x87)
{
int x = 0, y = 0;
inputByte = bzip2InputStream.ReadByte();
if (inputByte < 0)
{
return(null);
}
x = inputByte;
inputByte = bzip2InputStream.ReadByte();
if (inputByte < 0)
{
return(null);
}
y = inputByte;
y <<= 8;
x |= y;
inputByte = bzip2InputStream.ReadByte();
if (inputByte < 0)
{
return(null);
}
}
CBP2ReaderBranch readerBranch = new CBP2ReaderBranch();
CBP2ReaderBranch[] memoryLine = predictRemember();
bool returnAddressStackOffBy2 = false;
bool returnAddressStackOffBy3 = false;
if ((inputByte & 0x80) != 0)
{
if (inputByte == 0x82)
{
returnAddressStackOffBy2 = true;
}
else
{
if (inputByte == 0x83)
{
returnAddressStackOffBy3 = true;
}
else
{
return(null);
}
}
inputByte = bzip2InputStream.ReadByte();
if (inputByte < 0)
{
return(null);
}
}
bool correct = inputByte < BRANCH_MEMORY_ASSOCIATIVITY_SIZE * 2;
if (correct)
{
bool returnAddressStackCorrect = inputByte >= BRANCH_MEMORY_ASSOCIATIVITY_SIZE;
if (returnAddressStackCorrect)
{
inputByte -= BRANCH_MEMORY_ASSOCIATIVITY_SIZE;
}
readerBranch.address = memoryLine[inputByte].address;
readerBranch.targetAddress = memoryLine[inputByte].targetAddress;
readerBranch.taken = memoryLine[inputByte].taken;
readerBranch.code = memoryLine[inputByte].code;
if (readerBranch.code == 0x70)
{
long popped = popReturnAddressStack();
if (returnAddressStackCorrect)
{
readerBranch.targetAddress = (uint)popped;
if (returnAddressStackOffBy2)
{
readerBranch.targetAddress += 2;
}
else
{
if (returnAddressStackOffBy3)
{
readerBranch.targetAddress -= 3;
}
}
}
else
{
initReturnAddressStack();
}
}
if (!readerBranch.equal(memoryLine[inputByte], returnAddressStackCorrect))
{
return(null);
}
branch.branchInfo.address = readerBranch.address;
branch.targetAddress = readerBranch.targetAddress;
branch.branchTaken = readerBranch.taken;
updateRemember(readerBranch, memoryLine, true, (int)inputByte);
inputByte = readerBranch.code;
}
else
{
branch.branchInfo.address = readUint();
branch.targetAddress = readUint();
branch.branchTaken = true;
readerBranch.address = branch.branchInfo.address;
readerBranch.targetAddress = branch.targetAddress;
readerBranch.taken = branch.branchTaken;
readerBranch.code = inputByte;
// if this is a return, manage the return address stack
if (readerBranch.code == 0x70)
{
// could be a correct return address stack prediction but with incorrect call site???
long popped = popReturnAddressStack();
if (popped != branch.targetAddress && popped != branch.targetAddress - 2 && popped != branch.targetAddress + 3)
{
initReturnAddressStack();
}
}
updateRemember(readerBranch, memoryLine, false, -1);
}
branch.branchInfo.opcode = (uint)inputByte & 15;
inputByte >>= 4;
if (!correct)
{
classMisspredicted[inputByte]++;
}
switch (inputByte)
{
case 1: // taken conditional branch
branch.branchInfo.branchFlags |= BranchInfo.BR_CONDITIONAL;
break;
case 2: // not taken conditional branch
branch.branchTaken = false;
branch.branchInfo.branchFlags |= BranchInfo.BR_CONDITIONAL;
break;
case 3: // unconditional branch
break;
case 4: // indirect branch
branch.branchInfo.branchFlags |= BranchInfo.BR_INDIRECT;
break;
case 5: // call
branch.branchInfo.branchFlags |= BranchInfo.BR_CALL;
pushReturnAddressStack(branch.branchInfo.address + 5);
break;
case 6: // indirect call
branch.branchInfo.branchFlags |= BranchInfo.BR_CALL | BranchInfo.BR_INDIRECT;
pushReturnAddressStack(branch.branchInfo.address + 2);
break;
case 7: // return
branch.branchInfo.branchFlags |= BranchInfo.BR_RETURN;
break;
default:
return(null);
}
lastBranch = branch;
numberOfBranches++;
return(branch);
}
