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Understanding arrays using assembly.
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| contract AsmArray { | |
| uint256[] public arr; | |
| /// @dev Push some dummy data to begin with. | |
| constructor() { | |
| arr.push(1); | |
| arr.push(2); | |
| } | |
| /// @dev Function used to view the value of `arr[idx]`. | |
| /// This function will return 0 if out of bounds `idx` is provided. | |
| function viewStorageAtIdx(uint256 idx) external view returns (uint256) { | |
| assembly { | |
| mstore(0x00, arr.slot) | |
| mstore(0x40, sload(add(keccak256(0, 32), idx))) | |
| return(0x40, 32) | |
| } | |
| } | |
| /// @dev Function used to push a `val` to `arr`. | |
| function pushToArr(uint256 val) external { | |
| assembly { | |
| /// Reuse array length to avoid double sload. | |
| let len := sload(arr.slot) | |
| mstore(0x00, arr.slot) | |
| /// Store `val` in array at `len`. | |
| sstore(add(keccak256(0, 32), len), val) | |
| /// Increment value of `arr.slot` which is the length of the array by 1. | |
| sstore(arr.slot, add(len, 1)) | |
| } | |
| } | |
| /// @dev Function used to return the current length of `arr`. | |
| function getArrLength() external view returns (uint256) { | |
| assembly { | |
| /// Store the current length of `arr` in memory at fmp. | |
| mstore(0x40, sload(arr.slot)) | |
| return(0x40, 32) | |
| } | |
| } | |
| } |
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@ItsCuzzo Just fix minor bug on calculating slot of dynamic array.