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39 lines
1.4 KiB
39 lines
1.4 KiB
/** |
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* Tracks newlines during parsing in order to provide an efficient API for |
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* determining the one-indexed `{ line, col }` position for any offset |
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* within the input. |
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*/ |
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class LineCounter { |
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constructor() { |
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this.lineStarts = []; |
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/** |
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* Should be called in ascending order. Otherwise, call |
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* `lineCounter.lineStarts.sort()` before calling `linePos()`. |
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*/ |
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this.addNewLine = (offset) => this.lineStarts.push(offset); |
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/** |
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* Performs a binary search and returns the 1-indexed { line, col } |
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* position of `offset`. If `line === 0`, `addNewLine` has never been |
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* called or `offset` is before the first known newline. |
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*/ |
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this.linePos = (offset) => { |
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let low = 0; |
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let high = this.lineStarts.length; |
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while (low < high) { |
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const mid = (low + high) >> 1; // Math.floor((low + high) / 2) |
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if (this.lineStarts[mid] < offset) |
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low = mid + 1; |
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else |
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high = mid; |
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} |
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if (this.lineStarts[low] === offset) |
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return { line: low + 1, col: 1 }; |
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if (low === 0) |
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return { line: 0, col: offset }; |
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const start = this.lineStarts[low - 1]; |
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return { line: low, col: offset - start + 1 }; |
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}; |
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} |
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} |
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export { LineCounter };
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