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[refactor] interpreter: define interface for vfExec

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Includes comments added by Pieter Wuille.
This commit is contained in:
Anthony Towns 2019-09-18 15:49:29 +10:00 committed by Pieter Wuille
parent 89fb241c54
commit d0e8f4d5d8
1 changed files with 27 additions and 3 deletions
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30
src/script/interpreter.cpp
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@ -278,6 +278,30 @@ int FindAndDelete(CScript& script, const CScript& b)
return nFound;
}
namespace {
/** A data type to abstract out the condition stack during script execution.
*
* 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
* each.
*
* 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
* present at all. To implement OP_ELSE, a toggle_top modifier is added, which
* flips the last value without returning it.
*/
class ConditionStack {
private:
std::vector<bool> m_flags;
public:
bool empty() { return m_flags.empty(); }
bool all_true() { return !std::count(m_flags.begin(), m_flags.end(), false); }
void push_back(bool f) { m_flags.push_back(f); }
void pop_back() { m_flags.pop_back(); }
void toggle_top() { m_flags.back() = !m_flags.back(); }
};
}
bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptError* serror)
{
static const CScriptNum bnZero(0);
@ -293,7 +317,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
CScript::const_iterator pbegincodehash = script.begin();
opcodetype opcode;
valtype vchPushValue;
std::vector<bool> vfExec;
ConditionStack vfExec;
std::vector<valtype> altstack;
set_error(serror, SCRIPT_ERR_UNKNOWN_ERROR);
if (script.size() > MAX_SCRIPT_SIZE)
@ -305,7 +329,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
{
while (pc < pend)
{
bool fExec = !count(vfExec.begin(), vfExec.end(), false);
bool fExec = vfExec.all_true();
//
// Read instruction
@ -494,7 +518,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
{
if (vfExec.empty())
return set_error(serror, SCRIPT_ERR_UNBALANCED_CONDITIONAL);
vfExec.back() = !vfExec.back();
vfExec.toggle_top();
}
break;