作者samuelduan ()
看板EE_DSnP
标题Re: [讨论] BddNode and BddNodeInt
时间Mon Jan 8 21:07:47 2007
不好意思 我也想问一些很基本的问题...>"<
※ 引述《ric2k1 (Ric)》之铭言：
: 9. All the operations on BddNodeInt* need to go through BddNode ---
: * In the BddNode constructor, we increase the reference count of the
: BddNode::_node. So if a BddNode variable is declared, the reference
: count of its associated BddNodeInt* will be incremented by 1.
: * In the BddNode descructor, we decrease the reference count of the
: BddNode::_node. So if the program goes out of the scope of a certain
: BddNode variable, the reference count of its BddNodeInt* will be
: decremented by 1.
: * In the BddNode assignment '=' operator, for example, f = g, we first
: decrease the reference count of "f._node", and then increase the
: reference count of "g._node". Of course, we will asssign
: "f._node = g._node"
Q1: 我对 f = g 的领会是 f node 指向(还是应该说是连到?) g node
可以了解 g 的ref count要加1
但是为何 f 的ref count也要减1呢
f 本来的架构应该不会改变不是吗?
: 13. So we will take the advanatage of the fact that the pointer addresses are
: multiplier of 4, and we can use the lowest two bits to record the edge
: information. We use the lowest 1 bit to record the INVERSION.
: 14. To use the lower bits of a pointer variable, we need to conver it to a
: size_t variable, such as:
: v = size_t(n);
: and then the edge information can be added to it by v = v + 1.
: 15. Combining the above, we redefine the classes BddNode and BddNodeInt as...
: class BddNode {
: size_t _nodeV; // to hold BddNodeInt* and 1-bit edge info
: };
: class BddNodeInt {
: BddNode _left;
: BddNode _right;
: unsigned _level : 16;
: unsigned _refCount : 15;
: unsigned _visited : 1;
: };
Q2: 所以我可以把 size_t _nodeV 看成BddNodeInt* _node 有一样功能的data member
然後 BddNode::getBddNodeInt() 就是一个converter
只是有点看不懂 BDD_NODE_PTR_MASK的定义
((UNIT_MAX >> BDD_EDGE_BITS) << BDD_EDGE_BITS 是让这个 _nodeV 变成一个合理的
pointer address?
Q3: 在前面几篇有同学问到 BddNode::_one 和 BddNode::_zero
我比较疑问的是在 BddManager::init()中
BddNode::_one = BddNode(BddNodeInt::_terminal, BDD_POS_EDGE);
如果这里 _terminal = 0
那当呼叫到 BddNode::BddNode(BddNodeInt* n, BDD_EDGE_FLAG f) 时
其中的 assert(n!=0) 不是会有问题吗?
--
※ 发信站: 批踢踢实业坊(ptt.cc)
◆ From: 140.109.223.18