static int Execute(Instruction instr)
{
//First must set the operands
//Most will use RS and RT, which are EX.A and EX.B
int left = ctx.pipelineregs.RF__EX_A;
int right = ctx.pipelineregs.RF__EX_B;
if (instr.op == "ADDU" || instr.op == "SUBU" || instr.op == "ADDIU") //Unsigned instr, convert to bits and interpret as unsigned
{
//Left will still be an int, but its bit representation must be interpreted as uint, so we will convert the int to bits, those bits to uint, then that uint back to an int
left = (int)BitsToUInt(IntToBits(left));
right = (int)BitsToUInt(IntToBits(right));
}
if (TwoRegAndImmediateList.Contains(instr.op)) //Want to use immediate
{
right = instr.imm;
}
else if (TwoRegAndShamtList.Contains(instr.op))
{
left = (int)instr.shamt;
right = ctx.registers[(int)instr.rt];
}
else if (instr.op == "SW" || instr.op == "LW")
{
right = instr.offset;
}
//Now must check for forwarding which can overwrite previously set values
if (ctx.forwardvalues.Use_DF_To_EX_Left)
{
left = ctx.forwardvalues.DF_To_EX_Left_Value;
}
else if (ctx.forwardvalues.Use_DS_To_EX_Left)
{
left = ctx.forwardvalues.DS_To_EX_Left_Value;
}
else if (ctx.forwardvalues.Use_WB_To_EX_Left)
{
left = ctx.forwardvalues.WB_To_EX_Left_Value;
}
if (ctx.forwardvalues.Use_DF_To_EX_Right)
{
right = ctx.forwardvalues.DF_To_EX_Right_Value;
}
else if (ctx.forwardvalues.Use_DS_To_EX_Right)
{
right = ctx.forwardvalues.DS_To_EX_Right_Value;
}
else if (ctx.forwardvalues.Use_WB_To_EX_Right)
{
right = ctx.forwardvalues.WB_To_EX_Right_Value;
}
//Now perform operation
int a = left;
int b = right;
if (instr.op == "ADD" || instr.op == "ADDI" || instr.op == "ADDU" || instr.op == "ADDIU" || instr.op == "SW" || instr.op == "LW")
{
return(a + b);
}
else if (instr.op == "SUB" || instr.op == "SUBU")
{
return(a - b);
}
else if (instr.op == "AND")
{
return(a & b);
}
else if (instr.op == "OR")
{
return(a | b);
}
else if (instr.op == "XOR")
{
return(a ^ b);
}
else if (instr.op == "NOR")
{
return(~(a | b));
}
else if (instr.op == "SLL")
{
return(b << a);
}
else if (instr.op == "SRA")
{
return(b >> a);
}
else if (instr.op == "SRL")
{
return((int)((uint)b >> a));
}
else if (instr.op == "SLTI" || instr.op == "SLT")
{
return(a < b ? 1 : 0);
}
//Jumps and branches
else if (instr.op == "JR" || instr.op == "J")
{
ctx.takebranch = true;
return((int)instr.addr);
}
else if (BranchList.Contains(instr.op))
{
ctx.takebranch = ResolveBranch(instr, left, right);
return(instr.pc + 4 + instr.offset);
}
return(0);
}
