136 lines
4.1 KiB
JavaScript
136 lines
4.1 KiB
JavaScript
/*
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MIT License http://www.opensource.org/licenses/mit-license.php
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Author Mikola Lysenko @mikolalysenko
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*/
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"use strict";
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/* cspell:disable-next-line */
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// Refactor: Peter Somogyvari @petermetz
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/** @typedef {">=" | "<=" | "<" | ">" | "-" } BinarySearchPredicate */
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/** @typedef {"GE" | "GT" | "LT" | "LE" | "EQ" } SearchPredicateSuffix */
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/**
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* Helper function for compiling binary search functions.
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*
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* The generated code uses a while loop to repeatedly divide the search interval
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* in half until the desired element is found, or the search interval is empty.
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*
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* The following is an example of a generated function for calling `compileSearch("P", "c(x,y)<=0", true, ["y", "c"], false)`:
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*
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* ```js
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* function P(a,l,h,y,c){var i=l-1;while(l<=h){var m=(l+h)>>>1,x=a[m];if(c(x,y)<=0){i=m;l=m+1}else{h=m-1}}return i};
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* ```
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*
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* @param {string} funcName The name of the function to be compiled.
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* @param {string} predicate The predicate / comparison operator to be used in the binary search.
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* @param {boolean} reversed Whether the search should be reversed.
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* @param {string[]} extraArgs Extra arguments to be passed to the function.
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* @param {boolean=} earlyOut Whether the search should return as soon as a match is found.
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* @returns {string} The compiled binary search function.
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*/
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const compileSearch = (funcName, predicate, reversed, extraArgs, earlyOut) => {
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const code = [
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"function ",
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funcName,
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"(a,l,h,",
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extraArgs.join(","),
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"){",
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earlyOut ? "" : "var i=",
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reversed ? "l-1" : "h+1",
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";while(l<=h){var m=(l+h)>>>1,x=a[m]"
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];
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if (earlyOut) {
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if (predicate.indexOf("c") < 0) {
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code.push(";if(x===y){return m}else if(x<=y){");
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} else {
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code.push(";var p=c(x,y);if(p===0){return m}else if(p<=0){");
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}
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} else {
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code.push(";if(", predicate, "){i=m;");
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}
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if (reversed) {
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code.push("l=m+1}else{h=m-1}");
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} else {
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code.push("h=m-1}else{l=m+1}");
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}
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code.push("}");
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if (earlyOut) {
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code.push("return -1};");
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} else {
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code.push("return i};");
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}
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return code.join("");
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};
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/**
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* This helper functions generate code for two binary search functions:
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* A(): Performs a binary search on an array using the comparison operator specified.
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* P(): Performs a binary search on an array using a _custom comparison function_
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* `c(x,y)` **and** comparison operator specified by `predicate`.
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*
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* @param {BinarySearchPredicate} predicate The predicate / comparison operator to be used in the binary search.
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* @param {boolean} reversed Whether the search should be reversed.
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* @param {SearchPredicateSuffix} suffix The suffix to be used in the function name.
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* @param {boolean=} earlyOut Whether the search should return as soon as a match is found.
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* @returns {function} The compiled binary search function.
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*/
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const compileBoundsSearch = (predicate, reversed, suffix, earlyOut) => {
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const arg1 = compileSearch(
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"A",
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"x" + predicate + "y",
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reversed,
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["y"],
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earlyOut
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);
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const arg2 = compileSearch(
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"P",
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"c(x,y)" + predicate + "0",
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reversed,
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["y", "c"],
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earlyOut
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);
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const fnHeader = "function dispatchBinarySearch";
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const fnBody =
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"(a,y,c,l,h){\
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if(typeof(c)==='function'){\
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return P(a,(l===void 0)?0:l|0,(h===void 0)?a.length-1:h|0,y,c)\
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}else{\
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return A(a,(c===void 0)?0:c|0,(l===void 0)?a.length-1:l|0,y)\
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}}\
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return dispatchBinarySearch";
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const fnArgList = [arg1, arg2, fnHeader, suffix, fnBody, suffix];
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const fnSource = fnArgList.join("");
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const result = new Function(fnSource);
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return result();
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};
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/**
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* These functions are used to perform binary searches on arrays.
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*
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* @example
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* ```js
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* const { gt, le} = require("./binarySearchBounds");
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* const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
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*
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* // Find the index of the first element greater than 5
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* const index1 = gt(arr, 5); // index1 === 3
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*
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* // Find the index of the first element less than or equal to 5
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* const index2 = le(arr, 5); // index2 === 4
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* ```
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*/
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module.exports = {
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ge: compileBoundsSearch(">=", false, "GE"),
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gt: compileBoundsSearch(">", false, "GT"),
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lt: compileBoundsSearch("<", true, "LT"),
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le: compileBoundsSearch("<=", true, "LE"),
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eq: compileBoundsSearch("-", true, "EQ", true)
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};
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