Differential D8837 Diff 26774 src/script/interpreter.cpp

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src/script/interpreter.cpp

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	* Conceptually it acts like a vector of booleans, one for each level of nested			* Conceptually it acts like a vector of booleans, one for each level of nested
	* IF/THEN/ELSE, indicating whether we're in the active or inactive branch of			* IF/THEN/ELSE, indicating whether we're in the active or inactive branch of
	* each.			* each.
	*			*
	* The elements on the stack cannot be observed individually; we only need to			* The elements on the stack cannot be observed individually; we only need to
	* expose whether the stack is empty and whether or not any false values are			* expose whether the stack is empty and whether or not any false values are
	* present at all. To implement OP_ELSE, a toggle_top modifier is added, which			* present at all. To implement OP_ELSE, a toggle_top modifier is added, which
	* flips the last value without returning it.			* flips the last value without returning it.
				*
				* This uses an optimized implementation that does not materialize the
				* actual stack. Instead, it just stores the size of the would-be stack,
				* and the position of the first false value in it.
	*/			*/
	class ConditionStack {			class ConditionStack {
	private:			private:
	std::vector<bool> m_flags;			//! A constant for m_first_false_pos to indicate there are no falses.
				static constexpr uint32_t NO_FALSE = std::numeric_limits<uint32_t>::max();

				//! The size of the implied stack.
				uint32_t m_stack_size = 0;
				//! The position of the first false value on the implied stack, or NO_FALSE
				//! if all true.
				uint32_t m_first_false_pos = NO_FALSE;

	public:			public:
	bool empty() { return m_flags.empty(); }			bool empty() { return m_stack_size == 0; }
	bool all_true() {			bool all_true() { return m_first_false_pos == NO_FALSE; }
	return !std::count(m_flags.begin(), m_flags.end(), false);			void push_back(bool f) {
	}			if (m_first_false_pos == NO_FALSE && !f) {
	void push_back(bool f) { m_flags.push_back(f); }			// The stack consists of all true values, and a false is added.
	void pop_back() { m_flags.pop_back(); }			// The first false value will appear at the current size.
	void toggle_top() { m_flags.back() = !m_flags.back(); }			m_first_false_pos = m_stack_size;
				}
				++m_stack_size;
				}
				void pop_back() {
				assert(m_stack_size > 0);
				--m_stack_size;
				if (m_first_false_pos == m_stack_size) {
				// When popping off the first false value, everything becomes true.
				m_first_false_pos = NO_FALSE;
				}
				}
				void toggle_top() {
				assert(m_stack_size > 0);
				if (m_first_false_pos == NO_FALSE) {
				// The current stack is all true values; the first false will be the
				// top.
				m_first_false_pos = m_stack_size - 1;
				} else if (m_first_false_pos == m_stack_size - 1) {
				// The top is the first false value; toggling it will make
				// everything true.
				m_first_false_pos = NO_FALSE;
				} else {
				// There is a false value, but not on top. No action is needed as
				// toggling anything but the first false value is unobservable.
				}
				}
	};			};
	} // namespace			} // namespace

	bool EvalScript(std::vector<valtype> &stack, const CScript &script,			bool EvalScript(std::vector<valtype> &stack, const CScript &script,
	uint32_t flags, const BaseSignatureChecker &checker,			uint32_t flags, const BaseSignatureChecker &checker,
	ScriptExecutionMetrics &metrics, ScriptError *serror) {			ScriptExecutionMetrics &metrics, ScriptError *serror) {
	static const CScriptNum bnZero(0);			static const CScriptNum bnZero(0);
	static const CScriptNum bnOne(1);			static const CScriptNum bnOne(1);
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