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Question

I'm in the process of implementing a MIPS instruction set simulator. But when I try compiling my code, I keep getting "out of scope" errors and it's getting to be very frustrating. I've tried all kinds of variations, but nothing seems to be helping.
Here's my MIPSsim.cpp file

#include <iostream>
#include <fstream>
#include <string>
#include <cassert>

using namespace std;
const int BITS = 32;

string inst_decode(string line);
void execute(string line, string instruction, int &registers[]);
void print(int cycle, int inst_address, int regs[]/*, int data[]*/);
int convert_5(string binary);
int convert_32(string binary);
void add(string line, int &registers[]);
void sub(string line, int &registers[]);
void mult(string line, int &registers[]);


string inst_decode(string line){
    string instruction; 
    if(line.compare(0,1,"0") == 0){
        if (line.compare(1,5,"00010") == 0){
            cout << "JUMP" << endl;
            instruction = "JUMP";
        }else if (line.compare(1,5,"00100") == 0){
        cout << "BEQ" << endl;
        instruction = "BEQ";
    }else if (line.compare(1,5,"00001") == 0){
        cout << "BLTZ" << endl;
        instruction = "BLTZ";
    }else if (line.compare(1,5,"00111") == 0){
        cout << "BGTZ" << endl;
        instruction = "BGTZ";
    }else if (line.compare(1,5,"01011") == 0){
        cout << "SW" << endl;
        instruction = "SW";
    }else if (line.compare(1,5,"00011") == 0){
        cout << "LW" << endl;
        instruction = "LW";
    }else if (line.compare(1,5,"00010") == 0){
        cout << "SRL" << endl;
        instruction = "SRL";
    }else if ((line.compare(1,5,"11100") == 0)&&(line.compare(26,6,"000010") == 0)){
        cout << "MUL" << endl;
        instruction = "MUL";
    }else if (line.compare(1,5,"00000") == 0){
        if (line.compare(26,6,"100000") == 0){
            cout << "ADD" << endl;
            instruction = "ADD";
        }else if (line.compare(26,6,"100010") == 0){
            cout << "SUB" << endl;
            instruction = "SUB";
        }else if (line.compare(26,6,"100100") == 0){
            cout << "AND" << endl;
            instruction = "AND";
        }else if (line.compare(26,6,"100101") == 0){
            cout << "OR" << endl;
            instruction = "OR";
        }else if (line.compare(26,6,"101010") == 0){
            cout << "SLT" << endl;
            instruction = "SLT";
        }else if (line.compare(26,6,"000000") == 0){
            cout << "SLL" << endl;
            instruction = "SLL";
        }else if (line.compare(6,26,"00000000000000000000000000") == 0){
            cout << "NOP" << endl;
            instruction = "NOP";
        }
    }
    }else{
        if (line.compare(26,6,"100100") == 0){
            cout << "ADDI" << endl;
            instruction = "ADDI";
        }else if (line.compare(26,6,"100010") == 0){
            cout << "ANDI" << endl;
            instruction = "ANDI";
        }
    }
    return instruction;
}

void execute(string line, string instruction, int& registers[]){
    if(instruction == "ADD"){
        add(line, registers);
    }else if(instruction == "ADDI"){
        addi(line, registers);
    }else if(instruction == "SUB"){
        sub(line, registers);
    }else if(instruction == "MUL"){
        mult(line, registers);
    }
}

void print(int cycle, int inst_address, int regs[]/*, int data[][]*/){
    cout << "---------------------------\n";
    cout << "Cycle: " << cycle << "\t" << inst_address << "\t" << "\n";
    cout << "\nRegisters\n";
    cout << "R00:\t";
    for(int i=0; i<=15; i++){
        cout << regs[i] << "\t";
    }
    cout << "\nR16:\t";
    for(int i=16; i<32; i++){
            cout << regs[i] << "\t";
    }
    cout << "\n\nData\n";
        //cout << "\n148:\t";
        //for(int i=0; i<8; i++){
        //  cout << data[i] << "\t";
        //}
        //cout << "\n180:\t";
        //for(int i=9; i<17; i++){
            //  cout << data[i] << "\t";
        //}
        //cout << "\n212:\t";
        //for(int i=18; i<26; i++){
        //  cout << data[i] << "\t";
    //}
    cout << "\n";
}


int main(){
    int registers[32] = {0};
        //  int data[2][32];
    string inst;
    //int cycle = 1;
    //int PC = 64;
    string binary_inst[64];

    ifstream inFile;
    inFile.open("sample.txt");
    if (!inFile) {
        cout << "Unable to open file sample.txt" << endl;
        return 0;
    }
    string x;
    while(!inFile.eof()){
        for(int i=0; i<64; i++){
            inFile >> x;
            binary_inst[i] = x;
            inst = inst_decode(binary_inst[i]);
            execute(binary_inst[i], inst, registers);
            //print(cycle, PC, registers);
        }
    } 
    //  print(cycle, PC, registers);

    return 0;
}



int convert_5(string binary) {
    long power = 32;
    long sum = 0;
    assert(binary.size() == 5);

    for ( int i=0; i<BITS; ++i) {
        if ( i==0 && binary[i]!='0') {
            sum = -32;
        }
        else {
            sum += (binary[i]-'0')*power;
        }
        power /= 2;
    }
    return sum;
}

int convert_32(string binary) {
    long power = 4294967296;
    long sum = 0;
    assert(binary.size() == 32);

    for ( int i=0; i<BITS; ++i) {
        if ( i==0 && binary[i]!='0') {
            sum = -4294967296;
        }
        else {
            sum += (binary[i]-'0')*power;
        }
        power /= 2;
    }
    return sum;
}



void add(string line, int& registers[]){
    int dest = convert_5(line.substr(17,5));
    cout << "Dest: " << dest << endl;

    int target = convert_5(line.substr(12,5));
    cout << "Target: " << target << endl;

    int source = convert_5(line.substr(7,5));
    cout << "Source: " << source << endl;

    registers[dest] = registers[source] + registers[target];
    cout << "Addition: " << registers[dest] << endl;
}

void sub(string line, int& registers[]){
    int dest = convert_5(line.substr(17,5));
    cout << "Dest: " << dest << endl;

    int target = convert_5(line.substr(12,5));
    cout << "Target: " << target << endl;

    int source = convert_5(line.substr(7,5));
    cout << "Source: " << source << endl;

    registers[dest] = registers[source] - registers[target];
    cout << "Subtraction: " << registers[dest] << endl;
}

void mult(string line, int& registers[]){
    int dest = convert_5(line.substr(17,5));
    cout << "Dest: " << dest << endl;

    int target = convert_5(line.substr(12,5));
    cout << "Target: " << target << endl;

    int source = convert_5(line.substr(7,5));
    cout << "Source: " << source << endl;

    registers[dest] = registers[source] * registers[target];
    cout << "Multiplication: " << registers[dest] << endl;
}

Here are the error messages I keep getting:

lin114-08:10% make all
g++ -Wall -o MIPSsim MIPSsim.cpp
MIPSsim.cpp:10: error: declaration of ‘registers’ as array of references
MIPSsim.cpp:14: error: declaration of ‘registers’ as array of references
MIPSsim.cpp:15: error: declaration of ‘registers’ as array of references
MIPSsim.cpp:16: error: declaration of ‘registers’ as array of references
MIPSsim.cpp:85: error: declaration of ‘registers’ as array of references
MIPSsim.cpp: In function ‘void execute(...)’:
MIPSsim.cpp:86: error: ‘instruction’ was not declared in this scope
MIPSsim.cpp:87: error: ‘line’ was not declared in this scope
MIPSsim.cpp:87: error: ‘registers’ was not declared in this scope
MIPSsim.cpp:89: error: ‘line’ was not declared in this scope
MIPSsim.cpp:89: error: ‘registers’ was not declared in this scope
MIPSsim.cpp:89: error: ‘addi’ was not declared in this scope
MIPSsim.cpp:91: error: ‘line’ was not declared in this scope
MIPSsim.cpp:91: error: ‘registers’ was not declared in this scope
MIPSsim.cpp:93: error: ‘line’ was not declared in this scope
MIPSsim.cpp:93: error: ‘registers’ was not declared in this scope
MIPSsim.cpp: In function ‘int main()’:
MIPSsim.cpp:146: warning: cannot pass objects of non-POD type ‘struct std::string’     through ‘...’; call will abort at runtime
MIPSsim.cpp:146: warning: cannot pass objects of non-POD type ‘struct std::string’     through ‘...’; call will abort at runtime
MIPSsim.cpp: At global scope:
MIPSsim.cpp:193: error: declaration of ‘registers’ as array of references
MIPSsim.cpp: In function ‘void add(...)’:
MIPSsim.cpp:194: error: ‘line’ was not declared in this scope
MIPSsim.cpp:203: error: ‘registers’ was not declared in this scope
MIPSsim.cpp: At global scope:
MIPSsim.cpp:207: error: declaration of ‘registers’ as array of references
MIPSsim.cpp: In function ‘void sub(...)’:
MIPSsim.cpp:208: error: ‘line’ was not declared in this scope
MIPSsim.cpp:217: error: ‘registers’ was not declared in this scope
MIPSsim.cpp: At global scope:
MIPSsim.cpp:221: error: declaration of ‘registers’ as array of references
MIPSsim.cpp: In function ‘void mult(...)’:
MIPSsim.cpp:222: error: ‘line’ was not declared in this scope
MIPSsim.cpp:231: error: ‘registers’ was not declared in this scope
make: *** [MIPSsim] Error 1

Any help would be greatly appreciated

Answer 1

Always fix the first error the compiler gives you: int &registers[] won't work - use int * registers or int registers[] .

If you really want a reference to an array, you need to specify the size:

void execute(string line, string instruction, int (&registers) [10]);

All of these approaches will let you modify the actual array you pass to the function - there's no copying.

Side note:

In MIPSsim.cpp line 146 you're trying to pass a std::string to a vararg function (eg sprintf or printf ) - That won't work. Pass string.c_str() instead.

Answer 2

我不能说是否还有其他问题，但是我认为您的execute ， add ， sub ， mult函数只能将registers作为数组，而不是引用数组。

void add(string line, int registers[]);

Answer 3

You can't pass an array as an argument in C++. What you'd have to do is declare the parameters:

int (&registers)[32];

But registers aren't the only machine state which is likely to be changed by executing some code. A much better solution would be to define a struct with all of the machine state (except maybe the memory):

struct HWState
{
    int registers[32];
    unsigned cc;
    ??? pc;
    //  ...
};

Then pass that by reference, and you shouldn't have any problem. (In practice, C style arrays should only be used for static variables, with static initialization, and as members, when the count is constant and not too big.)

Answer 4

When you have a lot of functions that all take the same argument, that's usually a sign that they should be member functions. Here, you have add , sub and mult which all operate on your set of registers. And of course, most future instructions will too.

Therefore, define a class CPU with data members for each register (ie int r[32];float f[32]; , and a method CPU::add(std::string line) . Within add, you can just refer to r[4] if you need the first function argument register etc.