ranges.js

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This module directly ports some of the logic found in Python's range.

ranges.rangeEntry3(start, idx, step)

Returns the number at position idx in a range starting at start and iterating by step.

Arguments:

  • start (number)

  • idx (number)

  • step (number)

Returns:

number --

ranges.rangeEntry4(start, stop, idx, step)

Returns the number at position idx in the range [start, stop) and iterating by step.

Arguments:

  • start (number)

  • stop (number)

  • idx (number)

  • step (number)

Returns:

number|undefined --

 1/**
 2 * Returns the number at position ``idx`` in a range starting at ``start`` and iterating by ``step``.
 3 * @param {number} start
 4 * @param {number} idx
 5 * @param {number} step
 6 * @return {number}
 7 */
 8function rangeEntry3(start, idx, step) {
 9    return start + idx * step;
10}
11exports.rangeEntry3 = rangeEntry3;
12
13/**
14 * Returns the number at position ``idx`` in the range [``start``, ``stop``) and iterating by ``step``.
15 * @param {number} start
16 * @param {number} stop
17 * @param {number} idx
18 * @param {number} step
19 * @return {number | undefined}
20 */
21function rangeEntry4(start, stop, idx, step) {
22    let length = 0;
23    if (step > 0 && start < stop) {
24        length = Math.floor(1 + (stop - 1 - start) / step);
25    } else if (step < 0 && start > stop) {
26        length = Math.floor(1 + (start - 1 - stop) / (-step));
27    }
28    if (idx < 0) {
29        idx = length + idx;
30    }
31    if (idx < 0 || idx >= length) {
32        return undefined;
33    }
34    return rangeEntry3(start, idx, step);
35}
36exports.rangeEntry4 = rangeEntry4;