public_library_map/node_modules/nth-check/lib/compile.js
2021-09-05 10:12:48 +00:00

56 lines
1.9 KiB
JavaScript

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.compile = void 0;
var boolbase_1 = require("boolbase");
/**
* Returns a function that checks if an elements index matches the given rule
* highly optimized to return the fastest solution.
*
* @param parsed A tuple [a, b], as returned by `parse`.
* @returns A highly optimized function that returns whether an index matches the nth-check.
* @example
* const check = nthCheck.compile([2, 3]);
*
* check(0); // `false`
* check(1); // `false`
* check(2); // `true`
* check(3); // `false`
* check(4); // `true`
* check(5); // `false`
* check(6); // `true`
*/
function compile(parsed) {
var a = parsed[0];
// Subtract 1 from `b`, to convert from one- to zero-indexed.
var b = parsed[1] - 1;
/*
* When `b <= 0`, `a * n` won't be lead to any matches for `a < 0`.
* Besides, the specification states that no elements are
* matched when `a` and `b` are 0.
*
* `b < 0` here as we subtracted 1 from `b` above.
*/
if (b < 0 && a <= 0)
return boolbase_1.falseFunc;
// When `a` is in the range -1..1, it matches any element (so only `b` is checked).
if (a === -1)
return function (index) { return index <= b; };
if (a === 0)
return function (index) { return index === b; };
// When `b <= 0` and `a === 1`, they match any element.
if (a === 1)
return b < 0 ? boolbase_1.trueFunc : function (index) { return index >= b; };
/*
* Otherwise, modulo can be used to check if there is a match.
*
* Modulo doesn't care about the sign, so let's use `a`s absolute value.
*/
var absA = Math.abs(a);
// Get `b mod a`, + a if this is negative.
var bMod = ((b % absA) + absA) % absA;
return a > 1
? function (index) { return index >= b && index % absA === bMod; }
: function (index) { return index <= b && index % absA === bMod; };
}
exports.compile = compile;