#include <stdio.h>
#include <stdlib.h>

//--------------------------------------------------------------------------------------------------
//
// stage 2 of 3
//
// challenge:
//   reveal the solution within VM.mem
//
// disclaimer:
//   tested in ie 9, firefox 6, chrome 14 and v8 shell (http://code.google.com/apis/v8/build.html),
//   other javascript implementations may or may not work.
//
//--------------------------------------------------------------------------------------------------

typedef unsigned char byte;

struct {
    unsigned int ip;
    
    byte r0;
    byte r1;
    byte r2;
    byte r3;
    
    byte cs;
    byte ds;
    
    byte fl;
    
  }
cpu = { 
    /*ip:*/ 0x00,
    
    /*r0:*/ 0x00,
    /*r1:*/ 0x00,
    /*r2:*/ 0x00,
    /*r3:*/ 0x00,
    
    /*cs:*/ 0x00,
    /*ds:*/ 0x10,
    
    /*fl:*/ 0x00,
   };
   
byte mem[16*256+256] = {
    0x31, 0x04, 0x33, 0xaa, 0x40, 0x02, 0x80, 0x03, 0x52, 0x00, 0x72, 0x01, 0x73, 0x01, 0xb2, 0x50,
    0x30, 0x14, 0xc0, 0x01, 0x80, 0x00, 0x10, 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    
    0x98, 0xab, 0xd9, 0xa1, 0x9f, 0xa7, 0x83, 0x83, 0xf2, 0xb1, 0x34, 0xb6, 0xe4, 0xb7, 0xca, 0xb8,
    0xc9, 0xb8, 0x0e, 0xbd, 0x7d, 0x0f, 0xc0, 0xf1, 0xd9, 0x03, 0xc5, 0x3a, 0xc6, 0xc7, 0xc8, 0xc9,
    0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9,
    0xda, 0xdb, 0xa9, 0xcd, 0xdf, 0xdf, 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,
    0x26, 0xeb, 0xec, 0xed, 0xee, 0xef, 0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9,
    0x7d, 0x1f, 0x15, 0x60, 0x4d, 0x4d, 0x52, 0x7d, 0x0e, 0x27, 0x6d, 0x10, 0x6d, 0x5a, 0x06, 0x56,
    0x47, 0x14, 0x42, 0x0e, 0xb6, 0xb2, 0xb2, 0xe6, 0xeb, 0xb4, 0x83, 0x8e, 0xd7, 0xe5, 0xd4, 0xd9,
    0xc3, 0xf0, 0x80, 0x95, 0xf1, 0x82, 0x82, 0x9a, 0xbd, 0x95, 0xa4, 0x8d, 0x9a, 0x2b, 0x30, 0x69,
    0x4a, 0x69, 0x65, 0x55, 0x1c, 0x7b, 0x69, 0x1c, 0x6e, 0x04, 0x74, 0x35, 0x21, 0x26, 0x2f, 0x60,
    0x03, 0x4e, 0x37, 0x1e, 0x33, 0x54, 0x39, 0xe6, 0xba, 0xb4, 0xa2, 0xad, 0xa4, 0xc5, 0x95, 0xc8,
    0xc1, 0xe4, 0x8a, 0xec, 0xe7, 0x92, 0x8b, 0xe8, 0x81, 0xf0, 0xad, 0x98, 0xa4, 0xd0, 0xc0, 0x8d,
    0xac, 0x22, 0x52, 0x65, 0x7e, 0x27, 0x2b, 0x5a, 0x12, 0x61, 0x0a, 0x01, 0x7a, 0x6b, 0x1d, 0x67,
    0x75, 0x70, 0x6c, 0x1b, 0x11, 0x25, 0x25, 0x70, 0x7f, 0x7e, 0x67, 0x63, 0x30, 0x3c, 0x6d, 0x6a,
    0x01, 0x51, 0x59, 0x5f, 0x56, 0x13, 0x10, 0x43, 0x19, 0x18, 0xe5, 0xe0, 0xbe, 0xbf, 0xbd, 0xe9,
    0xf0, 0xf1, 0xf9, 0xfa, 0xab, 0x8f, 0xc1, 0xdf, 0xcf, 0x8d, 0xf8, 0xe7, 0xe2, 0xe9, 0x93, 0x8e,
    0xec, 0xf5, 0xc8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    
    0x37, 0x7a, 0x07, 0x11, 0x1f, 0x1d, 0x68, 0x25, 0x32, 0x77, 0x1e, 0x62, 0x23, 0x5b, 0x47, 0x55,
    0x53, 0x30, 0x11, 0x42, 0xf6, 0xf1, 0xb1, 0xe6, 0xc3, 0xcc, 0xf8, 0xc5, 0xe4, 0xcc, 0xc0, 0xd3,
    0x85, 0xfd, 0x9a, 0xe3, 0xe6, 0x81, 0xb5, 0xbb, 0xd7, 0xcd, 0x87, 0xa3, 0xd3, 0x6b, 0x36, 0x6f,
    0x6f, 0x66, 0x55, 0x30, 0x16, 0x45, 0x5e, 0x09, 0x74, 0x5c, 0x3f, 0x29, 0x2b, 0x66, 0x3d, 0x0d,
    0x02, 0x30, 0x28, 0x35, 0x15, 0x09, 0x15, 0xdd, 0xec, 0xb8, 0xe2, 0xfb, 0xd8, 0xcb, 0xd8, 0xd1,
    0x8b, 0xd5, 0x82, 0xd9, 0x9a, 0xf1, 0x92, 0xab, 0xe8, 0xa6, 0xd6, 0xd0, 0x8c, 0xaa, 0xd2, 0x94,
    0xcf, 0x45, 0x46, 0x67, 0x20, 0x7d, 0x44, 0x14, 0x6b, 0x45, 0x6d, 0x54, 0x03, 0x17, 0x60, 0x62,
    0x55, 0x5a, 0x4a, 0x66, 0x61, 0x11, 0x57, 0x68, 0x75, 0x05, 0x62, 0x36, 0x7d, 0x02, 0x10, 0x4b,
    0x08, 0x22, 0x42, 0x32, 0xba, 0xe2, 0xb9, 0xe2, 0xd6, 0xb9, 0xff, 0xc3, 0xe9, 0x8a, 0x8f, 0xc1,
    0x8f, 0xe1, 0xb8, 0xa4, 0x96, 0xf1, 0x8f, 0x81, 0xb1, 0x8d, 0x89, 0xcc, 0xd4, 0x78, 0x76, 0x61,
    0x72, 0x3e, 0x37, 0x23, 0x56, 0x73, 0x71, 0x79, 0x63, 0x7c, 0x08, 0x11, 0x20, 0x69, 0x7a, 0x14,
    0x68, 0x05, 0x21, 0x1e, 0x32, 0x27, 0x59, 0xb7, 0xcf, 0xab, 0xdd, 0xd5, 0xcc, 0x97, 0x93, 0xf2,
    0xe7, 0xc0, 0xeb, 0xff, 0xe9, 0xa3, 0xbf, 0xa1, 0xab, 0x8b, 0xbb, 0x9e, 0x9e, 0x8c, 0xa0, 0xc1,
    0x9b, 0x5a, 0x2f, 0x2f, 0x4e, 0x4e, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

  
  byte getReg( byte regnr )
  {
      if (regnr == 0) return cpu.r0;
      if (regnr == 1) return cpu.r1;
      if (regnr == 2) return cpu.r2;
      if (regnr == 3) return cpu.r3;
      if (regnr == 4) return cpu.cs;
      if (regnr == 5) return cpu.ds;
      printf("ERROR: getReg out of range %d\n", regnr);
      exit(1);
  }

  void setReg( byte regnr, byte v )
  {
      if (regnr == 0) { cpu.r0 = v; printf(" r0 = %d", v); return; }
      if (regnr == 1) { cpu.r1 = v; printf(" r1 = %d", v); return; }
      if (regnr == 2) { cpu.r2 = v; printf(" r2 = %d", v); return; }
      if (regnr == 3) { cpu.r3 = v; printf(" r3 = %d", v); return; }
      if (regnr == 4) { cpu.cs = v; printf(" cs = %d", v); return; }
      if (regnr == 5) { cpu.ds = v; printf(" ds = %d", v); return; }
      printf("ERROR: setReg out of range %d\n", regnr);
      exit(1);
  }
  
  byte getMem( byte seg, byte off )
  {
      unsigned int i = ((long)seg)*16 + off;
      //printf("(mem[%d:%d=%d]==%d)", seg, off, i, mem[i]);
      return mem[i];
  }

  void setMem( byte seg, byte off, byte v )
  {
      unsigned int i = ((long)seg)*16 + off;
    //if (i < 0 || i > 768)
    //    throw "setMem out of range "+seg+"*16+"+off+" = "+i;
      printf(" mem[%d:%d=%d] = %d", seg, off, i, v);
      mem[i] = v;
  }
  
  byte getMemIP()
  {
      return getMem(cpu.cs, cpu.ip++);
  }
  
  int main()
  {
    // virtual machine architecture
    // ++++++++++++++++++++++++++++
    //
    // segmented memory model with 16-byte segment size (notation seg:offset)
    //
    // 4 general-purpose registers (r0-r3)
    // 2 segment registers (cs, ds equiv. to r4, r5)
    // 1 flags register (fl)
    //
    // instruction encoding
    // ++++++++++++++++++++
    //
    //           byte 1               byte 2 (optional)
    // bits      [ 7 6 5 4 3 2 1 0 ]  [ 7 6 5 4 3 2 1 0 ]
    // opcode      - - -             
    // mod               -           
    // operand1            - - - -
    // operand2                         - - - - - - - -
    //
    // operand1 is always a register index
    // operand2 is optional, depending upon the instruction set specified below
    // the value of mod alters the meaning of any operand2
    //   0: operand2 = reg ix
    //   1: operand2 = fixed immediate value or target segment (depending on instruction)
    //
    // instruction set
    // +++++++++++++++
    // 
    // Notes:
    //   * r1, r2 => operand 1 is register 1, operand 2 is register 2
    //   * movr r1, r2 => move contents of register r2 into register r1
    // 
    // opcode | instruction | operands (mod 0) | operands (mod 1)
    // -------+-------------+------------------+-----------------
    // 0x00   | jmp         | r1               | r2:r1
    // 0x01   | movr        | r1, r2           | rx,   imm 
    // 0x02   | movm        | r1, [ds:r2]      | [ds:r1], r2
    // 0x03   | add         | r1, r2           | r1,   imm
    // 0x04   | xor         | r1, r2           | r1,   imm 
    // 0x05   | cmp         | r1, r2           | r1,   imm 
    // 0x06   | jmpe        | r1               | r2:r1
    // 0x07   | hlt         | N/A              | N/A
    //
    // flags
    // +++++
    // 
    // cmp r1, r2 instruction results in:
    //   r1 == r2 => fl = 0
    //   r1 < r2  => fl = 0xff
    //   r1 > r2  => fl = 1
    // 
    // jmpe r1
    //   => if (fl == 0) jmp r1
    //      else nop
    
    for(int count = 0; count < 10000; count++)
    //for(;;)
    {
        printf("%d ", cpu.ip);
        byte instr = getMemIP();
        
        byte opcode = instr >> 5;
        byte mode = 1 & (instr >> 4);
        byte oper1 = 15 & instr;
        printf("%d: opcode = %d, mode = %d, oper1 = %d - ", instr, opcode, mode, oper1);
        
        if (opcode == 0)
        {
            if (mode == 0)
            {
                printf("jmp r%d", oper1);
            }
            else
            {
                byte oper2 = getMemIP();
                printf("jmp %d:r%d", oper2, oper1);
                cpu.cs = oper2;
            }
               cpu.ip = getReg(oper1);
        }
        else if (opcode == 1)
        {
            byte oper2 = getMemIP();
            if (mode == 0)
            {
                printf("movr r%d, %d", oper1, oper2);
                setReg(oper1, getReg(oper2));
            }
            else
            {
                printf("movr r%d, %d", oper1, oper2);
                setReg(oper1, oper2);
            }
        }
        else if (opcode == 2)
        {
            byte oper2 = getMemIP();
            if (mode == 0)
            {
                printf("movm r%d, [ds:r%d]", oper1, oper2);
                setReg(oper1, getMem(cpu.ds, getReg(oper2)));
            }
            else
            {
                printf("movm [ds:r%d], r%d", oper1, oper2);
                setMem(cpu.ds, getReg(oper1), getReg(oper2));
            }
        }
        else if (opcode == 3)
        {
            byte oper2 = getMemIP();
            if (mode == 0)
            {
                printf("add r%d, %d", oper1, oper2);
                setReg(oper1, (getReg(oper1) + getReg(oper2))&255);
            }
            else
            {
                printf("add r%d, %d", oper1, oper2);
                setReg(oper1, (getReg(oper1) + oper2)&255);
            }
        }
        else if (opcode == 4)
        {
            byte oper2 = getMemIP();
            if (mode == 0)
            {
                printf("xor r%d, %d", oper1, oper2);
                setReg(oper1, getReg(oper1) ^ getReg(oper2));
            }
            else
            {
                printf("xor r%d, %d", oper1, oper2);
                setReg(oper1, getReg(oper1) ^ oper2);
            }
        }
        else if (opcode == 5)
        {
            byte oper2 = getMemIP();
            if (mode == 0)
            {
                printf("cmp r%d, %d", oper1, oper2);
                if (getReg(oper1) < getReg(oper2))
                    cpu.fl = 0xff;
                else if (getReg(oper1) > getReg(oper2))
                    cpu.fl = 1;
                else
                    cpu.fl = 0;
            }
            else
            {
                printf("cmp r%d, %d", oper1, oper2);
                if (getReg(oper1) < oper2)
                    cpu.fl = 0xff;
                else if (getReg(oper1) > oper2)
                    cpu.fl = 1;
                else
                    cpu.fl = 0;
            }
               printf(" fl = %d", cpu.fl);
        }
        else if (opcode == 6)
        {
            if (mode == 0)
            {
                printf("jmpe r%d", oper1);
                if (cpu.fl == 0)
                    cpu.ip = getReg(oper1);
                    
            }
            else
            {
                byte oper2 = getMemIP();
                printf("jmpe %d:r%d", oper2, oper1);
                if (cpu.fl == 0)
                {
                       cpu.cs = oper2;
                    cpu.ip = getReg(oper1);
                }
            }
        }
        else if (opcode == 7)
        {
            printf("hlt");
            break;
        }
        printf("\n");
    }
    
    for (int i = 0; i < 3*256; i++)
        if (mem[i] < ' ' || mem[i] > 127)
            printf("#%02X", mem[i]);
        else
            printf("%c", mem[i]);
    return -1;
  }