pragma solidity ^ 0.4.8;

/**
 * Math operations with safety checks
 */
contract SafeMath {
  function safeMul(uint256 a, uint256 b) internal returns(uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function safeDiv(uint256 a, uint256 b) internal returns(uint256) {
    assert(b > 0);
    uint256 c = a / b;
    assert(a == b * c + a % b);
    return c;
  }

  function safeSub(uint256 a, uint256 b) internal returns(uint256) {
    assert(b <= a);
    return a - b;
  }

  function safeAdd(uint256 a, uint256 b) internal returns(uint256) {
    uint256 c = a + b;
    assert(c >= a && c >= b);
    return c;
  }

  function assert(bool assertion) internal {
    if (!assertion) {
      revert();
    }
  }
}

contract VolTaToken is SafeMath {
  string public name;
  string public symbol;
  uint8 public decimals;
  uint256 public totalSupply;
  address public owner;

  /* This creates an array with all balances */
  mapping(address => uint256) public balanceOf;
  mapping(address => uint256) public freezeOf;
  mapping(address => mapping(address => uint256)) public allowance;

  /* This generates a public event on the blockchain that will notify clients */
  event Transfer(address indexed from, address indexed to, uint256 value);

  /* This notifies clients about the amount burnt */
  event Burn(address indexed from, uint256 value);

  /* This notifies clients about the amount frozen */
  event Freeze(address indexed from, uint256 value);

  /* This notifies clients about the amount unfrozen */
  event Unfreeze(address indexed from, uint256 value);

  /* Initializes contract with initial supply tokens to the creator of the contract */
  function VolTaToken() {
    balanceOf[msg.sender] = 8888000000000000;       // Give the creator all initial tokens
    totalSupply = 8888000000000000;                 // Update total supply
    name = 'VolTa Token';                          // Set the name for display purposes
    symbol = 'VT';                          // Set the symbol for display purposes
    decimals = 8;                            // Amount of decimals for display purposes
    owner = msg.sender;
  }

  /* Send tokens */
  function transfer(address _to, uint256 _value) {
    if (_to == 0x0) revert();                               // Prevent transfer to 0x0 address. Use burn() instead
    if (_value <= 0) revert();
    if (balanceOf[msg.sender] < _value) revert();           // Check if the sender has enough
    if (balanceOf[_to] + _value < balanceOf[_to]) revert(); // Check for overflows
    balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);              // Subtract from the sender
    balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to], _value);                            // Add the same to the recipient
    Transfer(msg.sender, _to, _value);                      // Notify anyone listening that this transfer took place
  }

  /* Allow another contract to spend some tokens in your behalf */
  function approve(address _spender, uint256 _value) returns(bool success) {
    require((_value == 0) || (allowance[msg.sender][_spender] == 0));
    if (_value <= 0) revert();
    allowance[msg.sender][_spender] = _value;
    return true;
  }

  /* Transfer tokens */
  function transferFrom(address _from, address _to, uint256 _value) returns(bool success) {
    if (_to == 0x0) revert();                                // Prevent transfer to 0x0 address. Use burn() instead
    if (_value <= 0) revert();
    if (balanceOf[_from] < _value) revert();                 // Check if the sender has enough
    if (balanceOf[_to] + _value < balanceOf[_to]) revert();  // Check for overflows
    if (_value > allowance[_from][msg.sender]) revert();     // Check allowance
    balanceOf[_from] = SafeMath.safeSub(balanceOf[_from], _value);                         // Subtract from the sender
    balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to], _value);                             // Add the same to the recipient
    allowance[_from][msg.sender] = SafeMath.safeSub(allowance[_from][msg.sender], _value);
    Transfer(_from, _to, _value);
    return true;
  }

  /* Destruction of the token */
  function burn(uint256 _value) returns(bool success) {
    if (balanceOf[msg.sender] < _value) revert();            // Check if the sender has enough
    if (_value <= 0) revert();
    balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);           // Subtract from the sender
    totalSupply = SafeMath.safeSub(totalSupply, _value);                                // Updates totalSupply
    Burn(msg.sender, _value);
    return true;
  }

  function freeze(uint256 _value) returns(bool success) {
    if (balanceOf[msg.sender] < _value) revert();            // Check if the sender has enough
    if (_value <= 0) revert();
    balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);             // Subtract from the sender
    freezeOf[msg.sender] = SafeMath.safeAdd(freezeOf[msg.sender], _value);               // Updates frozen tokens
    Freeze(msg.sender, _value);
    return true;
  }

  function unfreeze(uint256 _value) returns(bool success) {
    if (freezeOf[msg.sender] < _value) revert();            // Check if the sender has enough
    if (_value <= 0) revert();
    freezeOf[msg.sender] = SafeMath.safeSub(freezeOf[msg.sender], _value);              // Updates frozen tokens
    balanceOf[msg.sender] = SafeMath.safeAdd(balanceOf[msg.sender], _value);            // Add to the sender
    Unfreeze(msg.sender, _value);
    return true;
  }

  /* Prevents accidental sending of Ether */
  function () {
    revert();
  }
  /* token code by aminsire@gmail.com */
}