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80 lines
2.4 KiB
80 lines
2.4 KiB
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methods {
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totalSupply(uint256) returns uint256 envfree
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balanceOf(address, uint256) returns uint256 envfree
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exists_wrapper(uint256) returns bool envfree
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}
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/// given two different token ids, if totalSupply for one changes, then
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/// totalSupply for other must not
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rule token_totalSupply_independence(method f)
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filtered {
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f -> f.selector != safeBatchTransferFrom(address,address,uint256[],uint256[],bytes).selector
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}
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{
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uint256 token1; uint256 token2;
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require token1 != token2;
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uint256 token1_before = totalSupply(token1);
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uint256 token2_before = totalSupply(token2);
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env e; calldataarg args;
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f(e, args);
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uint256 token1_after = totalSupply(token1);
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uint256 token2_after = totalSupply(token2);
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assert token1_after != token1_before => token2_after == token2_before,
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"methods must not change the total supply of more than one token";
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}
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/******************************************************************************/
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ghost mapping(uint256 => mathint) sumOfBalances {
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init_state axiom forall uint256 token . sumOfBalances[token] == 0;
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}
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hook Sstore _balances[KEY uint256 token][KEY address user] uint256 newValue (uint256 oldValue) STORAGE {
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sumOfBalances[token] = sumOfBalances[token] + newValue - oldValue;
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}
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/// The sum of the balances over all users must equal the total supply for a
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/// given token.
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invariant total_supply_is_sum_of_balances(uint256 token)
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sumOfBalances[token] == totalSupply(token)
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{
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preserved {
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requireInvariant balanceOfZeroAddressIsZero(token);
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}
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}
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/******************************************************************************/
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/// The balance of a token for the zero address must be zero.
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invariant balanceOfZeroAddressIsZero(uint256 token)
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balanceOf(0, token) == 0
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/// If a user has a token, then the token should exist.
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rule held_tokens_should_exist {
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address user; uint256 token;
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requireInvariant balanceOfZeroAddressIsZero(token);
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// This assumption is safe because of total_supply_is_sum_of_balances
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require balanceOf(user, token) <= totalSupply(token);
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// note: `exists_wrapper` just calls `exists`
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assert balanceOf(user, token) > 0 => exists_wrapper(token),
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"if a user's balance for a token is positive, the token must exist";
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}
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/******************************************************************************/
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/*
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rule sanity {
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method f; env e; calldataarg args;
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f(e, args);
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assert false;
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}
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*/
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