8d6250cd5a
* 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.
(cherry picked from commit f7e53d90fa)
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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