简单MIPS汇编器

最新推荐文章于 2023-12-26 21:34:22 发布

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最新推荐文章于 2023-12-26 21:34:22 发布 · 5.4k 阅读

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#汇编 #MIPS

本文介绍了一个简单的MIPS汇编器，该汇编器能够读取包含add, sub, and, or, slt, beq, j, lw, sw, nop等指令的源代码，并将它们转换为机器码，输出到文本文件。虽然它不支持注释和所有MIPS指令，但对于完成计算机组成实验的基本需求已绰绰有余。" 6699441,1054688,STM32开发资源大全,"['嵌入式', 'STM32开发', '硬件资源']

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OTL终于能写出点实用的东西了。今天写的一个MIPS汇编器，能读入若干行MIPS指令，将其翻译成机器码，存入一个文本文件中。目前只能编译add, sub, and, or, slt, beq, j, lw, sw, nop这几种指令，并且不能识别注释。不过对于完成计算机组成实验来说足够了。

// A simple and naive MIPS assembler
// Use this command to make: g++ MIPS.cpp -o MIPS
// Usage: ./MIPS CodeFile
#include<iostream>
#include<stdio.h>
#include<memory.h>
#include<cstring>
#include<fstream>
#include<iomanip>
#include<cstdlib>
using namespace std;

// A function used to extract the register number from string "$xx"
int getReg(char* arg){
    int reg = 0;
    char *p = arg;
    while (*p == ' ') p++;       // Skip the space at the beginning
    if (*p == '$') p++;          
    else return -1;              // Unexpected charaters

    // Parse
    while(*p >= '0' && *p <= '9'){
        reg = 10 * reg + (*p - '0');
        p++;
    }
    while (*p == ' ') p++;               // Skip the space following the number
    if (*p != '\0') return -1;           // Unexpected characters
    else return reg;
}

// Output a binary number with a given length to an object of ostream
void printBin(int num, int digi, ostream& os){
    char *bin = new char[digi];
    memset(bin, '0', digi * sizeof(char));

    char *p = bin + (strlen(bin) - 1);
    int sign = (num >= 0)? 1: -1;
    num = num * sign;

    while (num > 0){
        if (num & 1) *p = '1';
        num >>= 1;
        p--;
    }
    // Transform to the 2's complement
    if (sign == -1){
        p = bin + (strlen(bin) - 1);
        while (p >= bin && *p != '1') p--;      // Find the last '1'
        if (p >= bin && *p == '1') p--;         // Skip the last '1'
        while (p >= bin) {
            *p = ('0' + '1') - *p;
            p--;
        }
    }
    os << bin;
    delete bin;
}
        

int main(int argc, char** argv){
    // Check the input
    if (argc != 2){
        cout << "Error: File name needed." << endl;
        exit(-1);
    }

    ifstream code(argv[1]);
    char *objname = new char[strlen(argv[1]) + 10];
    strcpy(objname, argv[1]);

    int i;
    // Find the suffix
    for (i = strlen(objname) - 1; i >= 0; i--) if (objname[i] == '.') break;
    // Give the output file a ".mips" suffix
    if (objname[i] == '.'){
         objname[i + 1] = '\0';
         strcat(objname, "mips");
    }
    else strcat(objname, ".mips");

    ofstream obj(objname);
    delete objname;
    
    /****************************************************
     The instruction strctures
     R-type: 
        +------------------------------------------------+
        | opcode | rs    | rt    | rd    | shamt | funct |
        |--------+-------+-------+-------+-------+-------|
        | 6-bit  | 5-bit | 5-bit | 5-bit | 5-bit | 6-bit |
        +------------------------------------------------+
     I-type:
        +------------------------------------------------+
        | opcode | rs    | rt    | immediate             |
        |--------+-------+-------+-----------------------|
        | 6-bit  | 5-bit | 5-bit | 16-bit                |
        +------------------------------------------------+