116 lines
2.7 KiB
TypeScript
116 lines
2.7 KiB
TypeScript
import type { SourceMapSegment, ReverseSegment } from './sourcemap-segment';
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import { COLUMN } from './sourcemap-segment';
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export type MemoState = {
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lastKey: number;
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lastNeedle: number;
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lastIndex: number;
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};
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export let found = false;
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/**
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* A binary search implementation that returns the index if a match is found.
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* If no match is found, then the left-index (the index associated with the item that comes just
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* before the desired index) is returned. To maintain proper sort order, a splice would happen at
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* the next index:
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*
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* ```js
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* const array = [1, 3];
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* const needle = 2;
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* const index = binarySearch(array, needle, (item, needle) => item - needle);
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*
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* assert.equal(index, 0);
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* array.splice(index + 1, 0, needle);
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* assert.deepEqual(array, [1, 2, 3]);
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* ```
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*/
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export function binarySearch(
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haystack: SourceMapSegment[] | ReverseSegment[],
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needle: number,
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low: number,
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high: number,
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): number {
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while (low <= high) {
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const mid = low + ((high - low) >> 1);
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const cmp = haystack[mid][COLUMN] - needle;
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if (cmp === 0) {
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found = true;
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return mid;
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}
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if (cmp < 0) {
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low = mid + 1;
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} else {
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high = mid - 1;
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}
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}
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found = false;
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return low - 1;
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}
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export function upperBound(
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haystack: SourceMapSegment[] | ReverseSegment[],
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needle: number,
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index: number,
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): number {
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for (let i = index + 1; i < haystack.length; index = i++) {
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if (haystack[i][COLUMN] !== needle) break;
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}
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return index;
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}
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export function lowerBound(
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haystack: SourceMapSegment[] | ReverseSegment[],
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needle: number,
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index: number,
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): number {
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for (let i = index - 1; i >= 0; index = i--) {
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if (haystack[i][COLUMN] !== needle) break;
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}
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return index;
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}
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export function memoizedState(): MemoState {
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return {
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lastKey: -1,
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lastNeedle: -1,
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lastIndex: -1,
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};
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}
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/**
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* This overly complicated beast is just to record the last tested line/column and the resulting
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* index, allowing us to skip a few tests if mappings are monotonically increasing.
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*/
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export function memoizedBinarySearch(
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haystack: SourceMapSegment[] | ReverseSegment[],
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needle: number,
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state: MemoState,
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key: number,
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): number {
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const { lastKey, lastNeedle, lastIndex } = state;
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let low = 0;
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let high = haystack.length - 1;
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if (key === lastKey) {
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if (needle === lastNeedle) {
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found = lastIndex !== -1 && haystack[lastIndex][COLUMN] === needle;
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return lastIndex;
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}
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if (needle >= lastNeedle) {
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// lastIndex may be -1 if the previous needle was not found.
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low = lastIndex === -1 ? 0 : lastIndex;
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} else {
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high = lastIndex;
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}
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}
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state.lastKey = key;
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state.lastNeedle = needle;
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return (state.lastIndex = binarySearch(haystack, needle, low, high));
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}
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