mips-disassembler/MIPSDisassembler.java at main · christalphilip/mips-disassembler · GitHub

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public class MIPSDisassembler {
    public static void disassemble(int instruction, int address) {
        int opcode = (instruction & 0xFC000000) >>> 26;
        // If opcode == 0, then this indicates an R-format instruction
        if (opcode == 0) {
            int destreg = (instruction & 0x0000F800) >>> 11;
            int src1reg = (instruction & 0x03E00000) >>> 21;
            int src2reg = (instruction & 0x001F0000) >>> 16;
            int shamt = (instruction & 0x000007C0) >>> 6;
            int funct = instruction & 0x3F;
            // Switch statement for r-format: add, sub, and, or, slt
            switch (funct) {
                case 0x20:
                    System.out.println(String.format("%X add $%d, $%d, $%d", address, destreg, src1reg, src2reg));
                    break;
                case 0x22:
                    System.out.println(String.format("%X sub $%d, $%d, $%d", address, destreg, src1reg, src2reg));
                    break;
                case 0x24:
                    System.out.println(String.format("%X and $%d, $%d, $%d", address, destreg, src1reg, src2reg));
                    break;
                case 0x25:
                    System.out.println(String.format("%X or $%d, $%d, $%d", address, destreg, src1reg, src2reg));
                    break;
                case 0x2A:
                    System.out.println(String.format("%X slt $%d, $%d, $%d", address, destreg, src1reg, src2reg));
                    break;
                default:
                    System.out.println(String.format("%X Unknown instruction", address));
                    break;
            }
        // If opcode does not equal 0, then this indicates an I-format instruction like lw, sw, beq, bne
        // load word
        } else if (opcode == 0x23) {
            int src1reg = (instruction & 0x03E00000) >>> 21;
            int src2reg = (instruction & 0x001F0000) >>> 16;
            short offset = (short) (instruction & 0xFFFF);
            System.out.println(String.format("%X lw $%d, %d($%d)", address, src1reg, offset, src2reg));
        // store word
        } else if (opcode == 0x2B) {
            int src1reg = (instruction & 0x03E00000) >>> 21;
            int src2reg = (instruction & 0x001F0000) >>> 16;
            short offset = (short) (instruction & 0xFFFF);
            System.out.println(String.format("%X sw $%d, %d($%d)", address, src1reg, offset, src2reg));
        // branch on equal
        } else if (opcode == 0x4) {
            int src1reg = (instruction & 0x03E00000) >>> 21;
            int src2reg = (instruction & 0x001F0000) >>> 16;
            short offset = (short) (instruction & 0xFFFF);
            int destAddress = address + 4 + (offset << 2);
            System.out.println(String.format("%X beq $%d, $%d, Address 0x%X", address, src1reg, src2reg, destAddress));
        // branch on not equal
        } else if (opcode == 0x5) {
            int src1reg = (instruction & 0x03E00000) >>> 21;
            int src2reg = (instruction & 0x001F0000) >>> 16;
            short offset = (short) (instruction & 0xFFFF);
            int destAddress = address + 4 + (offset << 2);
            System.out.println(String.format("%X bne $%d, $%d, Address 0x%X", address, src1reg, src2reg, destAddress));
        }
    }

    // Actual instructions we will be disassembling
    public static void main(String[] args) {
        int[] instructions = {
            0x032BA020, 0x8CE90014, 0x12A90003, 0x022DA822, 0xADB30020, 0x02697824, 0xAE8FFFF4,
            0x018C6020, 0x02A4A825, 0x158FFFF7, 0x8ECDFFF0
        };
        // Starting address
        int address = 0x9A040;
        // Calls disassemble method for each instruction and loops
        for (int instr : instructions) {
            disassemble(instr, address);
            address += 4;
        }
    }
}