/* Nga ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   Copyright (c) 2008 - 2019, Charles Childers
   Copyright (c) 2009 - 2010, Luke Parrish
   Copyright (c) 2010,        Marc Simpson
   Copyright (c) 2010,        Jay Skeer
   Copyright (c) 2011,        Kenneth Keating
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
typedef void (*Handler)(void);
#define CELL         int32_t
#define IMAGE_SIZE   524288 * 16
#define ADDRESSES    2048
#define STACK_DEPTH  512
#define NUM_DEVICES  0
enum vm_opcode {
  VM_NOP,  VM_LIT,    VM_DUP,   VM_DROP,    VM_SWAP,   VM_PUSH,  VM_POP,
  VM_JUMP, VM_CALL,   VM_CCALL, VM_RETURN,  VM_EQ,     VM_NEQ,   VM_LT,
  VM_GT,   VM_FETCH,  VM_STORE, VM_ADD,     VM_SUB,    VM_MUL,   VM_DIVMOD,
  VM_AND,  VM_OR,     VM_XOR,   VM_SHIFT,   VM_ZRET,   VM_END,   VM_IO_ENUM,
  VM_IO_QUERY,        VM_IO_INTERACT
};
#define NUM_OPS VM_IO_INTERACT + 1
CELL sp, rp, ip;
CELL data[STACK_DEPTH];
CELL address[ADDRESSES];
CELL memory[IMAGE_SIZE + 1];
Handler IO_deviceHandlers[NUM_DEVICES + 1];
Handler IO_queryHandlers[NUM_DEVICES + 1];
#define TOS  data[sp]
#define NOS  data[sp-1]
#define TORS address[rp]
CELL ngaLoadImage(char *imageFile) {
  FILE *fp;
  CELL imageSize;
  long fileLen;
  if ((fp = fopen(imageFile, "rb")) != NULL) {
    /* Determine length (in cells) */
    fseek(fp, 0, SEEK_END);
    fileLen = ftell(fp) / sizeof(CELL);
    rewind(fp);
    /* Read the file into memory */
    imageSize = fread(&memory, sizeof(CELL), fileLen, fp);
    fclose(fp);
  }
  else {
    printf("Unable to find the ngaImage!\n");
    exit(1);
  }
  return imageSize;
}
void ngaPrepare() {
  ip = sp = rp = 0;
  for (ip = 0; ip < IMAGE_SIZE; ip++)
    memory[ip] = VM_NOP;
  for (ip = 0; ip < STACK_DEPTH; ip++)
    data[ip] = 0;
  for (ip = 0; ip < ADDRESSES; ip++)
    address[ip] = 0;
}
void inst_nop() {
}
void inst_lit() {
  sp++;
  ip++;
  TOS = memory[ip];
}
void inst_dup() {
  sp++;
  data[sp] = NOS;
}
void inst_drop() {
  data[sp] = 0;
   if (--sp < 0)
     ip = IMAGE_SIZE;
}
void inst_swap() {
  CELL a;
  a = TOS;
  TOS = NOS;
  NOS = a;
}
void inst_push() {
  rp++;
  TORS = TOS;
  inst_drop();
}
void inst_pop() {
  sp++;
  TOS = TORS;
  rp--;
}
void inst_jump() {
  ip = TOS - 1;
  inst_drop();
}
void inst_call() {
  rp++;
  TORS = ip;
  ip = TOS - 1;
  inst_drop();
}
void inst_ccall() {
  CELL a, b;
  a = TOS; inst_drop();  /* False */
  b = TOS; inst_drop();  /* Flag  */
  if (b != 0) {
    rp++;
    TORS = ip;
    ip = a - 1;
  }
}
void inst_return() {
  ip = TORS;
  rp--;
}
void inst_eq() {
  NOS = (NOS == TOS) ? -1 : 0;
  inst_drop();
}
void inst_neq() {
  NOS = (NOS != TOS) ? -1 : 0;
  inst_drop();
}
void inst_lt() {
  NOS = (NOS < TOS) ? -1 : 0;
  inst_drop();
}
void inst_gt() {
  NOS = (NOS > TOS) ? -1 : 0;
  inst_drop();
}
void inst_fetch() {
  switch (TOS) {
    case -1: TOS = sp - 1; break;
    case -2: TOS = rp; break;
    case -3: TOS = IMAGE_SIZE; break;
    default: TOS = memory[TOS]; break;
  }
}
void inst_store() {
  memory[TOS] = NOS;
  inst_drop();
  inst_drop();
}
void inst_add() {
  NOS += TOS;
  inst_drop();
}
void inst_sub() {
  NOS -= TOS;
  inst_drop();
}
void inst_mul() {
  NOS *= TOS;
  inst_drop();
}
void inst_divmod() {
  CELL a, b;
  a = TOS;
  b = NOS;
  TOS = b / a;
  NOS = b % a;
}
void inst_and() {
  NOS = TOS & NOS;
  inst_drop();
}
void inst_or() {
  NOS = TOS | NOS;
  inst_drop();
}
void inst_xor() {
  NOS = TOS ^ NOS;
  inst_drop();
}
void inst_shift() {
  CELL y = TOS;
  CELL x = NOS;
  if (TOS < 0)
    NOS = NOS << (TOS * -1);
  else {
    if (x < 0 && y > 0)
      NOS = x >> y | ~(~0U >> y);
    else
      NOS = x >> y;
  }
  inst_drop();
}
void inst_zret() {
  if (TOS == 0) {
    inst_drop();
    ip = TORS;
    rp--;
  }
}
void inst_end() {
  ip = IMAGE_SIZE;
}
void inst_ie() {
  sp++;
  TOS = NUM_DEVICES;
}
void inst_iq() {
  CELL Device = TOS;
  inst_drop();
  IO_queryHandlers[Device]();
}
void inst_ii() {
  CELL Device = TOS;
  inst_drop();
  IO_deviceHandlers[Device]();
}
Handler instructions[NUM_OPS] = {
  inst_nop, inst_lit, inst_dup, inst_drop, inst_swap, inst_push, inst_pop,
  inst_jump, inst_call, inst_ccall, inst_return, inst_eq, inst_neq, inst_lt,
  inst_gt, inst_fetch, inst_store, inst_add, inst_sub, inst_mul, inst_divmod,
  inst_and, inst_or, inst_xor, inst_shift, inst_zret, inst_end, inst_ie,
  inst_iq, inst_ii
};
void ngaProcessOpcode(CELL opcode) {
  instructions[opcode]();
}
int ngaValidatePackedOpcodes(CELL opcode) {
  CELL raw = opcode;
  CELL current;
  int valid = -1;
  int i;
  for (i = 0; i < 4; i++) {
    current = raw & 0xFF;
    if (!(current >= 0 && current <= 29))
      valid = 0;
    raw = raw >> 8;
  }
  return valid;
}
void ngaProcessPackedOpcodes(CELL opcode) {
  CELL raw = opcode;
  int i;
  for (i = 0; i < 4; i++) {
    ngaProcessOpcode(raw & 0xFF);
    raw = raw >> 8;
  }
}
#ifdef STANDALONE
int main(int argc, char **argv) {
  ngaPrepare();
  if (argc == 2)
      ngaLoadImage(argv[1]);
  else
      ngaLoadImage("ngaImage");
  CELL opcode, i;
  ip = 0;
  while (ip < IMAGE_SIZE) {
    opcode = memory[ip];
    if (ngaValidatePackedOpcodes(opcode) != 0) {
      ngaProcessPackedOpcodes(opcode);
    } else if (opcode >= 0 && opcode < 27) {
      ngaProcessOpcode(opcode);
    } else {
      printf("Invalid instruction!\n");
      printf("At %d, opcode %d\n", ip, opcode);
      exit(1);
    }
    ip++;
  }
  for (i = 1; i <= sp; i++)
    printf("%d ", data[i]);
  printf("\n");
  exit(0);
}
#endif