Safe (in the C# sense) way to implement something with pointers

Question

            ...
            {
                int *r1, *r2;
                r1 = GetCorrectRegister(first);
                r2 = GetCorrectRegister(second);
                switch ((OpCode)current.opcode)
                {
                    case OpCode.ADDR:
                        r2 = r1 + r2;
                        break;
                }
            }
            ...

This is the obvious, easiest way to solve this problem. However, I'd prefer not to use an unsafe method if I can avoid it. Basically, I have a bunch of integers which represent registers. There are assembly instructions that take register mnemonics as arguments. I'd prefer not to have the logic to determine which variable to assign to in each branch of the switch statement or make some sort of kludgey GetRegisterValue(mnemonic) and SetRegisterValue(mnemonic) functions. Is there some C#y way to do something similar?

use Delegates in C# it can act as functional pointers

Nighil
– Nighil

2011-02-13 07:18:13 +00:00
Commented Feb 13, 2011 at 7:18 — Nighil
– Nighil, Commented Feb 13, 2011 at 7:18
r2=r1+r2 ? You meant *r2=*r1+*r2, didn't you?

Doc Brown
– Doc Brown

2011-02-13 07:42:04 +00:00
Commented Feb 13, 2011 at 7:42 — Doc Brown
– Doc Brown, Commented Feb 13, 2011 at 7:42
Yes, I meant *r2=*r1+*r2, sorry.

Paul
– Paul

2011-02-13 16:51:07 +00:00
Commented Feb 13, 2011 at 16:51 — Paul
– Paul, Commented Feb 13, 2011 at 16:51

Doc Brown · Accepted Answer · 2011-02-13 07:50:17Z

5

I have a bunch of integers which represent registers

The obvious thing here is not to have a bunch of integers. Create an array

 int[] registers = new int[NUMBER_OF_REGISTERS];

Your above code turns into

    {
            int r1Index, r2Index;
            r1Index = GetCorrectRegisterIndex(first);
            r2Index = GetCorrectRegisterIndex(second);
            switch ((OpCode)current.opcode)
            {
                case OpCode.ADDR:
                    registers[r1Index] = registers[r1Index] + registers[r2Index];
                    break;
            }


     }

Additionally, use an enum to create symbolic names for your register names where each name gives you the right index.

answered Feb 13, 2011 at 7:50

Doc Brown

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2 Comments

Paul Over a year ago

If I wanted to index into an array using an enum value, I'd have to cast every time, right? registers[(int)Registers.A]?

Doc Brown Over a year ago

@Paul: yes, that is true, read this SO post stackoverflow.com/questions/3091267/converting-enum-to-int for more information.

Jaroslav Jandek · Accepted Answer · 2011-02-13 09:22:06Z

1

How about using a class and ref parameters?

class Registers
{
    public int EAX;
    public int EBX;
    //...

    public void ExecuteBinaryOperation(int opCode, ref int r1, ref int r2)
    {
        // ...
        // binary operation ADD.
        r2 = r1 + r2;
        //...
    }
}

and in code:

registers.ExecuteBinaryOperation(0, ref registers.EAX, ref registers.EBX);

answered Feb 13, 2011 at 9:22

Jaroslav Jandek

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