C4C 1 Virtual Machine

#include <stdio.h>

unsigned int ROM[256] = {0x3FC02000, //Contents of ROM - 30 bits used
                         0x3FA00020,
                         0x3FE00000,
                         0x3EC0A000,
                         0x3EA02000,
                         0x3E000000};
unsigned int RAM[256];  //Contents of RAM - 30 bits used
unsigned char REG[16];  //Registers AX - PX - 8 bits used
unsigned char INST = 0; //Instruction pointer - 8 bits used
unsigned int currInst;  //Current instruction loaded
unsigned int state = 1; //State of the computer, on or off
unsigned char OPERANDA;  //Operand A
unsigned char OPERANDB;  //Operand B
unsigned char getData = '\0'; //Character received from input

void main() {
 //Need to understand file descriptors for STDIN and normal file to read stuff

    //Walking through each instruction and looping on overflow
    while (INST <= 256 && state == 1) {
        //printf("%d\n", INST); //Debug
        currInst = ROM[INST];       //Load instruction from ROM and increment instruction pointer
        ++INST;

        if ((0x3E000000 & currInst) == 0x3E000000) {    //If this is an instruction, identify instruction and execute it
            OPERANDA = (currInst << 11) >> 24;          //Get operand A value - from INST OPERANDA, OPERANDB
            OPERANDB = (currInst << 19) >> 24;          //Get operand B value
            //printf("Cell: %d Inst: %x Operand A: %x Operand B: %x\n", INST - 1, ((currInst << 7) >> 28), OPERANDA, OPERANDB); //Debug

            switch ((currInst << 7) >> 28) {
                case 0:         //HALT
                    state = 0;
                    break;
                case 1:         //MOV
                    REG[OPERANDA] = REG[OPERANDB];
                    break;
                case 2:         //STORE
                    RAM[OPERANDA] = REG[OPERANDB];
                    break;
                case 3:         //LOADRAM
                    REG[OPERANDA] = RAM[OPERANDB];
                    break;
                case 4:         //LOADROM
                    REG[OPERANDA] = ROM[OPERANDB];
                    break;
                case 5:         //JMP
                    INST = OPERANDA;
                    break;
                case 6:         //JZ
                    if (REG[OPERANDB] == 0) {
                        INST = OPERANDA;
                    }
                    break;
                case 7:         //JNZ
                    if (REG[OPERANDB] != 0) {
                        INST = OPERANDA;
                    }
                    break;
                case 8:         //OR
                    REG[OPERANDA] |= REG[OPERANDB];
                    break;
                case 9:         //AND
                    REG[OPERANDA] &= REG[OPERANDB];
                    break;
                case 10:            //NOT
                    ~REG[OPERANDA];
                    break;
                case 11:            //SHL
                    REG[OPERANDA] << 1;
                    break;
                case 12:            //SHR
                    REG[OPERANDA] >> 1;
                    break;
                case 13:            //ADD
                    REG[OPERANDA] += REG[OPERANDB];
                    break;
                case 14:            //RECV
                    while (!(getData >= 'a' && getData <= 'f') && !(getData >= 'A' && getData <= 'F') && !(getData >= '0' && getData <= '9')) {
                        getData = getchar();
                    }
                    if (getData >= 'a' && getData <= 'f') {
                        getData -= ('a' - 0xA);
                    }
                    if (getData >= 'A' && getData <= 'F') {
                        getData -= ('A' - 0xA);
                    }
                    if (getData >= '0' && getData <= '9') {
                        getData -= '0';
                    }
                    REG[OPERANDA] = getData;
                    getData = '\0';
                    rewind(stdin);
                    break;
                case 15:            //SEND
                    printf("%x\n", REG[OPERANDA]);
                    break;
            }
        }
    }
}