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main.c
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main.c
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#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/time.h>
#include <unistd.h>
#include <sys/termios.h>
#include <signal.h>
// memory
uint16_t memory[UINT16_MAX];
// registers
enum {
R_R0 = 0,
R_R1,
R_R2,
R_R3,
R_R4,
R_R5,
R_R6,
R_R7,
R_PC,
R_COND,
R_COUNT,
};
uint16_t reg[R_COUNT];
enum
{
OP_BR = 0, /* branch */
OP_ADD, /* add */
OP_LD, /* load */
OP_ST, /* store */
OP_JSR, /* jump register */
OP_AND, /* bitwise and */
OP_LDR, /* load register */
OP_STR, /* store register */
OP_RTI, /* unused */
OP_NOT, /* bitwise not */
OP_LDI, /* load indirect */
OP_STI, /* store indirect */
OP_JMP, /* jump */
OP_RES, /* reserved (unused) */
OP_LEA, /* load effective address */
OP_TRAP /* execute trap */
};
// conditional flags
enum {
FLAG_POS = 1 << 0,
FLAG_ZRO = 1 << 1,
FLAG_NEG = 1 << 2,
};
enum
{
TRAP_GETC = 0x20, /* get character from keyboard, not echoed onto the terminal */
TRAP_OUT = 0x21, /* output a character */
TRAP_PUTS = 0x22, /* output a word string */
TRAP_IN = 0x23, /* get character from keyboard, echoed onto the terminal */
TRAP_PUTSP = 0x24, /* output a byte string */
TRAP_HALT = 0x25 /* halt the program */
};
enum
{
MR_KBSR = 0xFE00, /* keyboard status */
MR_KBDR = 0xFE02 /* keyboard data */
};
void update_flags(uint16_t r0){
if(reg[r0]>>15 == 1){
reg[R_COND] = FLAG_NEG;
}else if(reg[r0] == 0){
reg[R_COND] = FLAG_ZRO;
}else{
reg[R_COND] = FLAG_POS;
}
}
uint16_t sign_extend(uint16_t x, int bit_count)
{
if ((x >> (bit_count - 1)) & 1) {
x |= (0xFFFF << bit_count);
}
return x;
}
uint16_t swap16(uint16_t x)
{
return (x << 8) | (x >> 8);
}
uint16_t check_key()
{
fd_set readfds;
FD_ZERO(&readfds);
FD_SET(STDIN_FILENO, &readfds);
struct timeval timeout;
timeout.tv_sec = 0;
timeout.tv_usec = 0;
return select(1, &readfds, NULL, NULL, &timeout) != 0;
}
uint16_t mem_read(uint16_t addr){
if(addr == MR_KBSR){
if(check_key()){
memory[MR_KBSR] = 1 << 15;
memory[MR_KBDR] = getchar();
}else{
memory[MR_KBSR] = 0;
}
}
uint16_t val = memory[addr];
return val;
}
void mem_write(uint16_t addr, uint16_t val){
memory[addr] = val;
}
int load_program_from_file(const char* file){
FILE* image= fopen(file,"rb");
if(!image){
return 0;
}
uint16_t origin;
fread(&origin,sizeof(origin),1,image);
origin = swap16(origin);
uint16_t max_read = UINT16_MAX - origin;
uint16_t* i = memory + origin;
size_t read = fread(i,sizeof(uint16_t),max_read,image);
// swap
while(read-- > 0){
*i = swap16(*i);
++i;
}
return 1;
}
void op_add(uint16_t instr){
// rister to store results
uint16_t dr = (instr >> 9) & 0x7;
//sr1 register
uint16_t sr1 = (instr >> 6) & 0x7;
//imm flag
uint16_t imm_flag = (instr >> 5) & 0x1;
if(imm_flag){
uint16_t imm = instr & 0x1f;
reg[dr] = reg[sr1] + sign_extend(imm,5);
}else{
uint16_t sr2 = instr & 0x7;
reg[dr] = reg[sr1] + reg[sr2];
}
update_flags(dr);
}
void op_and(uint16_t instr){
uint16_t dr = (instr >> 9) & 0x7;
uint16_t sr1 = (instr >> 6) & 0x7;
uint16_t imm_flag = (instr >> 5) & 0x1;
if (imm_flag){
uint16_t imm = instr & 0x1f;
reg[dr] = reg[sr1] & sign_extend(imm,5);
}else{
reg[dr] = reg[sr1] & reg[(instr & 0x7)];
}
update_flags(dr);
}
void op_br(uint16_t ins){
uint16_t f = (ins >> 9) & 0x7;
uint16_t pc_offset = sign_extend((ins & 0x1ff),9);
if(f & reg[R_COND]){
reg[R_PC] += pc_offset;
}
}
void op_jmp(uint16_t ins){
uint16_t r = (ins >> 6) & 0x7;
reg[R_PC] = reg[r];
}
void op_jsr(uint16_t ins){
reg[R_R7] = reg[R_PC];
uint16_t f = (ins >> 11) & 1;
if(f){
// jsr
reg[R_PC] += sign_extend((ins & 0x7ff),11);
}else{
// jssr
reg[R_PC] = (ins >> 6) & 0x7;
}
}
void op_ld(uint16_t ins){
uint16_t dr = (ins >> 9) & 0x7;
uint16_t addr = sign_extend((ins & 0x1ff),9) + reg[R_PC];
reg[dr] = mem_read(addr);
update_flags(dr);
}
void op_ldi(uint16_t ins){
uint16_t dr = (ins >> 9) & 0x7;
uint16_t addr = sign_extend((ins & 0x1ff),9) + reg[R_PC];
reg[dr] = mem_read(mem_read(addr));
update_flags(dr);
}
void op_ldr(uint16_t ins){
uint16_t dr = (ins >> 9) & 0x7;
uint16_t addr = reg[(ins>>6) & 0x7] + sign_extend(ins & 0x3f,6);
reg[dr] = mem_read(addr);
update_flags(dr);
}
void op_lea(uint16_t ins){
uint16_t dr = (ins >> 9) & 0x7;
uint16_t addr = sign_extend(ins & 0x1ff,9) + reg[R_PC];
reg[dr] = addr;
update_flags(dr);
}
void op_not(uint16_t ins){
uint16_t dr = (ins >> 9) & 0x7;
uint16_t sr = (ins >> 6) & 0x7;
reg[dr] = ~reg[sr];
update_flags(dr);
}
void op_st(uint16_t ins){
uint16_t sr = (ins >> 9) & 0x7;
uint16_t addr = sign_extend(ins & 0x1ff, 9) + reg[R_PC];
uint16_t val = reg[sr];
mem_write(addr,val);
}
void op_sti(uint16_t ins){
uint16_t sr = (ins >> 9) & 0x7;
uint16_t addr = sign_extend(ins & 0x1ff, 9) + reg[R_PC];
uint16_t val = reg[sr];
mem_write(mem_read(addr),val);
}
void op_str(uint16_t ins){
uint16_t sr = (ins >> 9) & 0x7;
uint16_t br = (ins >> 6) & 0x7;
uint16_t addr = reg[br] + sign_extend(ins & 0x3f,6);
mem_write(addr, reg[sr]);
}
void trap_puts(){
uint16_t* c = memory + reg[R_R0];
while(*c){
putc((char)*c,stdout);
++c;
}
fflush(stdout);
}
void trap_getc(){
uint16_t c = (uint16_t)getchar();
reg[R_R0] = c;
}
void trap_out(){
putc((char)reg[R_R0],stdout);
fflush(stdout);
}
void trap_putsp(){
// 2 chars, in big endian c1 0:8,c2 9:15
uint16_t* c = memory + reg[R_R0];
while(*c){
// c1
putc((char)((*c)&0xff),stdout);
// c2
char c2 = (*c) >> 8;
if(c2){
putc(c2,stdout);
}
++c;
}
fflush(stdout);
}
/* Input Buffering */
struct termios original_tio;
void disable_input_buffering()
{
tcgetattr(STDIN_FILENO, &original_tio);
struct termios new_tio = original_tio;
new_tio.c_lflag &= ~ICANON & ~ECHO;
tcsetattr(STDIN_FILENO, TCSANOW, &new_tio);
}
void restore_input_buffering()
{
tcsetattr(STDIN_FILENO, TCSANOW, &original_tio);
}
void handle_interrupt(int signal)
{
restore_input_buffering();
printf("\n");
exit(-2);
}
void setup(){
signal(SIGINT, handle_interrupt);
disable_input_buffering();
}
int main(int argc, const char* argv[]){
if(argc != 2){
printf("Usage: ./lc3 <program>");
exit(2);
}
if(!load_program_from_file(argv[1])){
printf("Unable to load program from file %s",argv[2]);
exit(2);
}
setup();
int running = 1;
while (running)
{
uint16_t instr = mem_read(reg[R_PC]++);
uint16_t op = instr >> 12;
switch (op)
{
case OP_ADD:
op_add(instr);
break;
case OP_AND:
op_and(instr);
break;
case OP_BR:
op_br(instr);
break;
case OP_JMP:
op_jmp(instr);
break;
case OP_JSR:
op_jsr(instr);
break;
case OP_LD:
op_ld(instr);
break;
case OP_LDI:
op_ldi(instr);
break;
case OP_LDR:
op_ldr(instr);
break;
case OP_LEA:
op_lea(instr);
break;
case OP_NOT:
op_not(instr);
break;
case OP_ST:
op_st(instr);
break;
case OP_STI:
op_sti(instr);
break;
case OP_STR:
op_str(instr);
break;
case OP_TRAP:
switch(instr & 0xff){
case TRAP_PUTS:
trap_puts();
break;
case TRAP_GETC:
trap_getc();
break;
case TRAP_OUT:
trap_out();
break;
case TRAP_PUTSP:
trap_putsp();
break;
case TRAP_HALT:
puts("HALTING");
fflush(stdout);
running = 0;
break;
}
break;
case OP_RES:
case OP_RTI:
default:
abort();
break;
}
}
restore_input_buffering();
return 0;
}