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range.ts
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range.ts
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function* positiveRange(start: number, stop: number, step: number): IterableIterator<number> {
// r[i] = start + step*i where i >= 0 and r[i] < stop
for (let i = start; i < stop; i += step) {
yield i;
}
}
function* negativeRange(start: number, stop: number, step: number): IterableIterator<number> {
// r[i] = start + step*i where i >= 0 and r[i] > stop
for (let i = start; i > stop; i += step) {
yield i;
}
}
function makeIterator(start: number, stop: number, step: number): IterableIterator<number> {
if (start === 0 && step === 1) {
// The simple case is always faster using the Array.keys iterator
return Array(stop).keys();
}
if (step < 0) {
return negativeRange(start, stop, step);
}
return positiveRange(start, stop, step);
}
interface RangeIterator extends IterableIterator<number> {
indexOf(value: number): number;
}
function annotate(iterator: IterableIterator<number>, start: number, stop: number, step: number): RangeIterator {
const range = iterator as RangeIterator;
range.indexOf = function indexOf(value: number): number {
if (value >= stop || value < start) return -1;
const idx = value - start;
if (step === 1) return idx;
return Math.trunc((value - start) / step);
};
return range;
}
/**
* Returns an iterator of numbers and is commonly used for looping a specific number of times in for loops.
* The API is the same as Python's range.
* @return iterable iterator over range
*/
export function range(stop: number): RangeIterator;
export function range(start: number, stop: number): RangeIterator;
export function range(start: number, stop: number, step: number): RangeIterator;
export function range(...args: number[]): RangeIterator {
let stop = 0, start = 0, step = 1;
if (args.length === 1) {
[stop] = args;
} else {
[start, stop, step = 1] = args;
}
const it = makeIterator(start, stop, step);
return annotate(it, start, stop, step);
}