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121 lines
3.7 KiB
121 lines
3.7 KiB
"use strict";
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var __importDefault = (this && this.__importDefault) || function (mod) {
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return (mod && mod.__esModule) ? mod : { "default": mod };
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};
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.generate = exports.compile = void 0;
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var boolbase_1 = __importDefault(require("boolbase"));
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/**
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* Returns a function that checks if an elements index matches the given rule
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* highly optimized to return the fastest solution.
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*
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* @param parsed A tuple [a, b], as returned by `parse`.
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* @returns A highly optimized function that returns whether an index matches the nth-check.
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* @example
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*
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* ```js
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* const check = nthCheck.compile([2, 3]);
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*
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* check(0); // `false`
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* check(1); // `false`
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* check(2); // `true`
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* check(3); // `false`
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* check(4); // `true`
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* check(5); // `false`
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* check(6); // `true`
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* ```
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*/
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function compile(parsed) {
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var a = parsed[0];
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// Subtract 1 from `b`, to convert from one- to zero-indexed.
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var b = parsed[1] - 1;
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/*
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* When `b <= 0`, `a * n` won't be lead to any matches for `a < 0`.
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* Besides, the specification states that no elements are
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* matched when `a` and `b` are 0.
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*
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* `b < 0` here as we subtracted 1 from `b` above.
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*/
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if (b < 0 && a <= 0)
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return boolbase_1.default.falseFunc;
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// When `a` is in the range -1..1, it matches any element (so only `b` is checked).
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if (a === -1)
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return function (index) { return index <= b; };
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if (a === 0)
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return function (index) { return index === b; };
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// When `b <= 0` and `a === 1`, they match any element.
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if (a === 1)
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return b < 0 ? boolbase_1.default.trueFunc : function (index) { return index >= b; };
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/*
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* Otherwise, modulo can be used to check if there is a match.
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*
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* Modulo doesn't care about the sign, so let's use `a`s absolute value.
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*/
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var absA = Math.abs(a);
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// Get `b mod a`, + a if this is negative.
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var bMod = ((b % absA) + absA) % absA;
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return a > 1
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? function (index) { return index >= b && index % absA === bMod; }
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: function (index) { return index <= b && index % absA === bMod; };
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}
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exports.compile = compile;
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/**
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* Returns a function that produces a monotonously increasing sequence of indices.
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*
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* If the sequence has an end, the returned function will return `null` after
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* the last index in the sequence.
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*
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* @param parsed A tuple [a, b], as returned by `parse`.
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* @returns A function that produces a sequence of indices.
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* @example <caption>Always increasing (2n+3)</caption>
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*
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* ```js
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* const gen = nthCheck.generate([2, 3])
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*
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* gen() // `1`
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* gen() // `3`
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* gen() // `5`
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* gen() // `8`
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* gen() // `11`
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* ```
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*
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* @example <caption>With end value (-2n+10)</caption>
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*
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* ```js
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*
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* const gen = nthCheck.generate([-2, 5]);
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*
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* gen() // 0
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* gen() // 2
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* gen() // 4
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* gen() // null
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* ```
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*/
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function generate(parsed) {
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var a = parsed[0];
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// Subtract 1 from `b`, to convert from one- to zero-indexed.
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var b = parsed[1] - 1;
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var n = 0;
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// Make sure to always return an increasing sequence
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if (a < 0) {
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var aPos_1 = -a;
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// Get `b mod a`
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var minValue_1 = ((b % aPos_1) + aPos_1) % aPos_1;
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return function () {
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var val = minValue_1 + aPos_1 * n++;
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return val > b ? null : val;
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};
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}
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if (a === 0)
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return b < 0
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? // There are no result — always return `null`
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function () { return null; }
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: // Return `b` exactly once
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function () { return (n++ === 0 ? b : null); };
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if (b < 0) {
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b += a * Math.ceil(-b / a);
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}
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return function () { return a * n++ + b; };
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}
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exports.generate = generate;
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//# sourceMappingURL=compile.js.map
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