f7e53d90fa
* Add Arrays library with unit tests (#1209) * prepared due to snapshot token requirements * add library with method to find upper bound * add unit test for basic and edge cases * Imporove documentation for Arrays library Simplify Arrays.test.js to use short arrays as test date * Added comment for uint256 mid variable. * Explaned why uint256 mid variable calculated as Math.average is safe to use as index of array.
57 lines
1.6 KiB
Solidity
57 lines
1.6 KiB
Solidity
pragma solidity ^0.4.23;
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import "../math/Math.sol";
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/**
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* @title Arrays
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* @dev Utility library of inline array functions
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*/
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library Arrays {
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/**
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* @dev Upper bound search function which is kind of binary search algoritm. It searches sorted
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* array to find index of the element value. If element is found then returns it's index otherwise
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* it returns index of first element which is grater than searched value. If searched element is
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* bigger than any array element function then returns first index after last element (i.e. all
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* values inside the array are smaller than the target). Complexity O(log n).
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* @param array The array sorted in ascending order.
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* @param element The element's value to be find.
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* @return The calculated index value. Returns 0 for empty array.
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*/
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function findUpperBound(
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uint256[] storage array,
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uint256 element
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)
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internal
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view
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returns (uint256)
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{
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if (array.length == 0) {
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return 0;
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}
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uint256 low = 0;
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uint256 high = array.length;
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while (low < high) {
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uint256 mid = Math.average(low, high);
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// Note that mid will always be strictly less than high (i.e. it will be a valid array index)
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// because Math.average rounds down (it does integer division with truncation).
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if (array[mid] > element) {
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high = mid;
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} else {
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low = mid + 1;
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}
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}
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// At this point `low` is the exclusive upper bound. We will return the inclusive upper bound.
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if (low > 0 && array[low - 1] == element) {
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return low - 1;
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} else {
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return low;
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}
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}
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}
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