Add safeDiv and min/max functions to SafeMath

contracts/SafeMath.sol

@@ -11,6 +11,13 @@ contract SafeMath {
     return c;
   }
 
+  function safeDiv(uint a, uint b) internal returns (uint) {
+    assert(b > 0);
+    uint c = a / b;
+    assert(a == b * c + a % b);
+    return c;
+  }
+
   function safeSub(uint a, uint b) internal returns (uint) {
     assert(b <= a);
     return a - b;
@@ -22,6 +29,22 @@ contract SafeMath {
     return c;
   }
 
+  function max64(uint64 a, uint64 b) internal constant returns (uint64) {
+    return a >= b ? a : b;
+  }
+
+  function min64(uint64 a, uint64 b) internal constant returns (uint64) {
+    return a < b ? a : b;
+  }
+
+  function max256(uint256 a, uint256 b) internal constant returns (uint256) {
+    return a >= b ? a : b;
+  }
+
+  function min256(uint256 a, uint256 b) internal constant returns (uint256) {
+    return a < b ? a : b;
+  }
+
   function assert(bool assertion) internal {
     if (!assertion) throw;
   }