Merge pull request #27 from maraoz/token

Token improvements

contracts/ERC20.sol

 pragma solidity ^0.4.0;
+
+
+// see https://github.com/ethereum/EIPs/issues/20
+
 contract ERC20 {
     function totalSupply() constant returns (uint);
     function balanceOf(address who) constant returns (uint);

contracts/SafeMath.sol

+pragma solidity ^0.4.0;
+
+/**
+ * Math operations with safety checks
+ */
+contract SafeMath {
+  function safeMul(uint a, uint b) internal returns (uint) {
+    uint c = a * b;
+    assert(a == 0 || c / a == b);
+    return c;
+  }
+
+  function safeSub(uint a, uint b) internal returns (uint) {
+    assert(b <= a);
+    return a - b;
+  }
+
+  function safeAdd(uint a, uint b) internal returns (uint) {
+    uint c = a + b;
+    assert(c>=a && c>=b);
+    return c;
+  }
+
+  function assert(bool assertion) internal {
+    if (!assertion) throw;
+  }
+}
+

contracts/StandardToken.sol

+pragma solidity ^0.4.0;
+
+import './ERC20.sol';
+import './SafeMath.sol';
+
+/**
+ * ERC20 token
+ *
+ * https://github.com/ethereum/EIPs/issues/20
+ * Based on code by FirstBlood:
+ * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
+ */
+contract StandardToken is ERC20, SafeMath {
+
+  mapping(address => uint256) balances;
+  mapping (address => mapping (address => uint256)) allowed;
+  uint256 public totalSupply;
+
+  function transfer(address _to, uint256 _value) returns (bool success) {
+    if (balances[msg.sender] < _value) {
+      throw;
+    } 
+    balances[msg.sender] = safeSub(balances[msg.sender], _value);
+    balances[_to] = safeAdd(balances[_to], _value);
+    Transfer(msg.sender, _to, _value);
+    return true;
+  }
+
+  function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
+    var _allowance = allowed[_from][msg.sender];
+    if (balances[_from] < _value ||
+        _allowance < _value)) {
+      throw;
+    }
+
+    balances[_to] = safeAdd(balances[_to], _value);
+    balances[_from] = safeSub(balances[_from], _value);
+    allowed[_from][msg.sender] = safeSub(_allowance, _value);
+    Transfer(_from, _to, _value);
+    return true;
+  }
+
+  function balanceOf(address _owner) constant returns (uint256 balance) {
+    return balances[_owner];
+  }
+
+  function approve(address _spender, uint256 _value) returns (bool success) {
+    allowed[msg.sender][_spender] = _value;
+    Approval(msg.sender, _spender, _value);
+    return true;
+  }
+
+  function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
+    return allowed[_owner][_spender];
+  }
+
+}

contracts/Token.sol

-pragma solidity ^0.4.0;
-// Source: https://github.com/nexusdev/erc20
-// Flat file implementation of `dappsys/token/base.sol::DSTokenBase`
-
-// Everything throws instead of returning false on failure.
-import './ERC20.sol';
-
-contract Token is ERC20 {
-
-  mapping( address => uint ) _balances;
-  mapping( address => mapping( address => uint ) ) _approvals;
-  uint _supply;
-
-  function Token( uint initial_balance ) {
-    _balances[msg.sender] = initial_balance;
-    _supply = initial_balance;
-  }
-
-  function totalSupply() constant returns (uint supply) {
-    return _supply;
-  }
-
-  function balanceOf( address who ) constant returns (uint value) {
-    return _balances[who];
-  }
-
-  function transfer( address to, uint value) returns (bool ok) {
-    if( _balances[msg.sender] < value ) {
-        throw;
-    }
-    if( !safeToAdd(_balances[to], value) ) {
-        throw;
-    }
-    _balances[msg.sender] -= value;
-    _balances[to] += value;
-    Transfer( msg.sender, to, value );
-    return true;
-  }
-
-  function transferFrom( address from, address to, uint value) returns (bool ok) {
-    // if you don't have enough balance, throw
-    if( _balances[from] < value ) {
-        throw;
-    }
-    // if you don't have approval, throw
-    if( _approvals[from][msg.sender] < value ) {
-        throw;
-    }
-    if( !safeToAdd(_balances[to], value) ) {
-        throw;
-    }
-    // transfer and return true
-    _approvals[from][msg.sender] -= value;
-    _balances[from] -= value;
-    _balances[to] += value;
-    Transfer( from, to, value );
-    return true;
-  }
-
-  function approve(address spender, uint value) returns (bool ok) {
-    _approvals[msg.sender][spender] = value;
-    Approval( msg.sender, spender, value );
-    return true;
-  }
-
-  function allowance(address owner, address spender) constant returns (uint _allowance) {
-    return _approvals[owner][spender];
-  }
-
-  function safeToAdd(uint a, uint b) internal returns (bool) {
-    return (a + b >= a);
-  }
-}