[refactor] interpreter: define interface for vfExec
Includes comments added by Pieter Wuille.
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1 changed files with 27 additions and 3 deletions
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@ -278,6 +278,30 @@ int FindAndDelete(CScript& script, const CScript& b)
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return nFound;
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}
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namespace {
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/** A data type to abstract out the condition stack during script execution.
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*
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* Conceptually it acts like a vector of booleans, one for each level of nested
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* IF/THEN/ELSE, indicating whether we're in the active or inactive branch of
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* each.
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*
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* The elements on the stack cannot be observed individually; we only need to
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* expose whether the stack is empty and whether or not any false values are
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* present at all. To implement OP_ELSE, a toggle_top modifier is added, which
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* flips the last value without returning it.
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*/
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class ConditionStack {
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private:
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std::vector<bool> m_flags;
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public:
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bool empty() { return m_flags.empty(); }
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bool all_true() { return !std::count(m_flags.begin(), m_flags.end(), false); }
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void push_back(bool f) { m_flags.push_back(f); }
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void pop_back() { m_flags.pop_back(); }
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void toggle_top() { m_flags.back() = !m_flags.back(); }
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};
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}
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bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptError* serror)
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{
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static const CScriptNum bnZero(0);
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@ -293,7 +317,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
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CScript::const_iterator pbegincodehash = script.begin();
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opcodetype opcode;
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valtype vchPushValue;
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std::vector<bool> vfExec;
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ConditionStack vfExec;
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std::vector<valtype> altstack;
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set_error(serror, SCRIPT_ERR_UNKNOWN_ERROR);
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if (script.size() > MAX_SCRIPT_SIZE)
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@ -305,7 +329,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
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{
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while (pc < pend)
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{
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bool fExec = !count(vfExec.begin(), vfExec.end(), false);
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bool fExec = vfExec.all_true();
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//
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// Read instruction
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@ -494,7 +518,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
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{
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if (vfExec.empty())
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return set_error(serror, SCRIPT_ERR_UNBALANCED_CONDITIONAL);
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vfExec.back() = !vfExec.back();
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vfExec.toggle_top();
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}
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break;
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