assm-test/src/disass.c

#include "../includes/disass.h"
#include <stdlib.h>

const unsigned char* Image;
const unsigned char COPYMASKREG = 0x20;
const unsigned char COPYMASKADD = 0xA0;
const unsigned char ADDMASK     = 0x40;
const unsigned char SUBMASK     = 0x60;
const unsigned char CMPMASK     = 0x80;

const unsigned char REGMASK     = 0x00;//0x18; //0001 1000
const unsigned char CONSTMASK   = 0x08; //0000 1000
const unsigned char ADDRESSMASK = 0x10; //0001 0000

int IsRegisterPattern(unsigned char pattern, char* lexeme);
void GetParameter(unsigned char instruction, char* text);

void Disassemble(unsigned char image[HIGHMEMORY]) {
    Image = image;
    int position = image[0] + image[1];
    int end = image[2] + image[3];

    char* parameter1 = calloc(32, sizeof(char));
    char* parameter2 = calloc(32, sizeof(char));

    unsigned char instruction = image[position];

    while(end > position) {
        unsigned char masked = instruction & 0xE0;

        if (masked) {
            IsRegisterPattern(instruction & 0x07, parameter1);
            unsigned char parameterType = instruction & 0x18;

            if (parameterType == REGMASK) {
                IsRegisterPattern(Image[position + 1], parameter2);
                position += 2;
            } else if (parameterType == CONSTMASK) {
                snprintf(parameter2, sizeof(char) * 31, "%d", Image[position + 1] + Image[position + 2]);
                position += 3;
            }
            else if (parameterType == ADDRESSMASK) {
                snprintf(parameter2, sizeof(char) * 31, "[%#04X]", Image[position + 1] + Image[position + 2]);
                position += 3;
            }

            //If the top bits are set
            if (masked == COPYMASKREG) {
                printf("COPY %s, %s\n", parameter1, parameter2);
            }
            else if (masked == COPYMASKADD) {
                printf("COPY %s, %s\n", parameter2, parameter1);
            }
            else if (masked == ADDMASK) {
                printf("ADD %s, %s\n", parameter1, parameter2);
            }
            else if (masked == SUBMASK) {
                printf("SUB %s, %s\n", parameter1, parameter2);
            }
            else if (masked == CMPMASK) {
                printf("CMP %s, %s\n", parameter1, parameter2);
            }
            else {
                fprintf(stderr, "[Error] Unknown opcode %#02X\n", masked);
                exit(1);
            }
        }
        else {
            int parameter = Image[position + 1] + Image[position + 2];

            switch(instruction) {
                case 0:
                    printf("NOP\n");
                    position++;
                    break;
                case 1:
                    printf("JZ [%#04X]\n", parameter);
                    position += 3;
                    break;
                case 2:
                    printf("INT %d\n", parameter);
                    position += 3;
                    break;
                case 3:
                    printf("YLD\n");
                    position++;
                    break;
                case 4:
                    printf("RET\n");
                    position++;
                    break;
                case 5:
                    printf("CALL [%#04X]\n", parameter);
                    position += 3;
                    break;
                case 6:
                    printf("JMP [%#04X]\n", parameter);
                    position += 3;
                    break;
                case 7:
                    printf("IN %d\n", parameter);
                    position += 3;
                    break;
                case 8:
                    printf("OUT %d\n", parameter);
                    position += 3;
                    break;
                default:
                    position++;
                    break;
            }
        }

        instruction = Image[position];

        memset(parameter1, '\0', sizeof(char) * 32);
        memset(parameter2, '\0', sizeof(char) * 32);
    }
}

int IsRegisterPattern(unsigned char pattern, char* lexeme) {
    if (pattern > 8) {
        lexeme[0] = '\0';
        return 0;
    }
    //The registers' bit patterns are zero indexed, so 'r1' is '000'
    //but 'r8' is '111' and so forth.
    pattern++;

    lexeme[0] = 'r';
    lexeme[1] = pattern | 0x30;
    lexeme[2] = '\0';

    return 1;
}
/*
//REG       XXX0 0XXX
//Constant  XXX0 1XXX
//Address   XXX1 0XXX
    NOP  - 0000 0000 NOP
    JZ   - 0000 0001 JZ Address
    INT  - 0000 0010 INT Constant
    YLD  - 0000 0011 YLD
    RET  - 0000 0100 RET
    CALL - 0000 0101 CALL Address
    JMP  - 0000 0110 JMP Address
    IN   - 0000 0111 IN Constant
    OUT  - 0000 1000 OUT Constant
    COPY - 0010 0XXX COPY REG, REG
         - 0010 1XXX COPY REG, Constant
         - 0011 0XXX COPY REG, Address
         - 1010 0XXX COPY Address, REG
         - 1010 1XXX COPY Address, Constant
         - 1011 0XXX COPY Address, Address
    ADD  - 0100 0XXX ADD REG, REG
         - 0100 1XXX ADD REG, Constant
    SUB  - 0110 0XXX SUB REG, REG
         - 0110 1XXX SUB REG, Constant
    CMP  - 1000 0XXX CMP REG, REG
         - 1000 1XXX CMP REG, Constant
         - 1001 0XXX CMP REG, Address */