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pragma solidity ^0.4.11;
import "../Oracles/Oracle.sol";
/// @title Majority oracle contract - Allows to resolve an event based on multiple oracles with majority vote
/// @author Stefan George - <stefan@gnosis.pm>
contract MajorityOracle is Oracle {
/*
* Storage
*/
Oracle[] public oracles;
/*
* Public functions
*/
/// @dev Allows to create an oracle for a majority vote based on other oracles
/// @param _oracles List of oracles taking part in the majority vote
constructor(Oracle[] _oracles)
public
{
// At least 2 oracles should be defined
require(_oracles.length > 2);
for (uint i = 0; i < _oracles.length; i++)
// Oracle address cannot be null
require(address(_oracles[i]) != address(0));
oracles = _oracles;
}
/// @dev Allows to registers oracles for a majority vote
/// @return Is outcome set?
/// @return Outcome
function getStatusAndOutcome()
public
view
returns (bool outcomeSet, int outcome)
{
uint i;
int[] memory outcomes = new int[](oracles.length);
uint[] memory validations = new uint[](oracles.length);
for (i = 0; i < oracles.length; i++)
if (oracles[i].isOutcomeSet()) {
int _outcome = oracles[i].getOutcome();
for (uint j = 0; j <= i; j++)
if (_outcome == outcomes[j]) {
validations[j] += 1;
break;
}
else if (validations[j] == 0) {
outcomes[j] = _outcome;
validations[j] = 1;
break;
}
}
uint outcomeValidations = 0;
uint outcomeIndex = 0;
for (i = 0; i < oracles.length; i++)
if (validations[i] > outcomeValidations) {
outcomeValidations = validations[i];
outcomeIndex = i;
}
// There is a majority vote
if (outcomeValidations * 2 > oracles.length) {
outcomeSet = true;
outcome = outcomes[outcomeIndex];
}
}
/// @dev Returns if winning outcome is set
/// @return Is outcome set?
function isOutcomeSet()
public
view
returns (bool)
{
(bool outcomeSet, ) = getStatusAndOutcome();
return outcomeSet;
}
/// @dev Returns winning outcome
/// @return Outcome
function getOutcome()
public
view
returns (int)
{
(, int winningOutcome) = getStatusAndOutcome();
return winningOutcome;
}
}
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