/* -*- Mode: js; js-indent-level: 2; -*- */
/*
* Copyright 2011 Mozilla Foundation and contributors
* Licensed under the New BSD license. See LICENSE or:
* http://opensource.org/licenses/BSD-3-Clause
*/
exports.GREATEST_LOWER_BOUND = 1;
exports.LEAST_UPPER_BOUND = 2;
/**
* Recursive implementation of binary search.
*
* @param aLow Indices here and lower do not contain the needle.
* @param aHigh Indices here and higher do not contain the needle.
* @param aNeedle The element being searched for.
* @param aHaystack The non-empty array being searched.
* @param aCompare Function which takes two elements and returns -1, 0, or 1.
* @param aBias Either 'binarySearch.GREATEST_LOWER_BOUND' or
* 'binarySearch.LEAST_UPPER_BOUND'. Specifies whether to return the
* closest element that is smaller than or greater than the one we are
* searching for, respectively, if the exact element cannot be found.
*/
function recursiveSearch(aLow, aHigh, aNeedle, aHaystack, aCompare, aBias) {
// This function terminates when one of the following is true:
//
// 1. We find the exact element we are looking for.
//
// 2. We did not find the exact element, but we can return the index of
// the next-closest element.
//
// 3. We did not find the exact element, and there is no next-closest
// element than the one we are searching for, so we return -1.
var mid = Math.floor((aHigh - aLow) / 2) + aLow;
var cmp = aCompare(aNeedle, aHaystack[mid], true);
if (cmp === 0) {
// Found the element we are looking for.
return mid;
}
else if (cmp > 0) {
// Our needle is greater than aHaystack[mid].
if (aHigh - mid > 1) {
// The element is in the upper half.
return recursiveSearch(mid, aHigh, aNeedle, aHaystack, aCompare, aBias);
}
// The exact needle element was not found in this haystack. Determine if
// we are in termination case (3) or (2) and return the appropriate thing.
if (aBias == exports.LEAST_UPPER_BOUND) {
return aHigh < aHaystack.length ? aHigh : -1;
} else {
return mid;
}
}
else {
// Our needle is less than aHaystack[mid].
if (mid - aLow > 1) {
// The element is in the lower half.
return recursiveSearch(aLow, mid, aNeedle, aHaystack, aCompare, aBias);
}
// we are in termination case (3) or (2) and return the appropriate thing.
if (aBias == exports.LEAST_UPPER_BOUND) {
return mid;
} else {
return aLow < 0 ? -1 : aLow;
}
}
}
/**
* This is an implementation of binary search which will always try and return
* the index of the closest element if there is no exact hit. This is because
* mappings between original and generated line/col pairs are single points,
* and there is an implicit region between each of them, so a miss just means
* that you aren't on the very start of a region.
*
* @param aNeedle The element you are looking for.
* @param aHaystack The array that is being searched.
* @param aCompare A function which takes the needle and an element in the
* array and returns -1, 0, or 1 depending on whether the needle is less
* than, equal to, or greater than the element, respectively.
* @param aBias Either 'binarySearch.GREATEST_LOWER_BOUND' or
* 'binarySearch.LEAST_UPPER_BOUND'. Specifies whether to return the
* closest element that is smaller than or greater than the one we are
* searching for, respectively, if the exact element cannot be found.
* Defaults to 'binarySearch.GREATEST_LOWER_BOUND'.
*/
exports.search = function search(aNeedle, aHaystack, aCompare, aBias) {
if (aHaystack.length === 0) {
return -1;
}
var index = recursiveSearch(-1, aHaystack.length, aNeedle, aHaystack,
aCompare, aBias || exports.GREATEST_LOWER_BOUND);
if (index < 0) {
return -1;
}
// We have found either the exact element, or the next-closest element than
// the one we are searching for. However, there may be more than one such
// element. Make sure we always return the smallest of these.
while (index - 1 >= 0) {
if (aCompare(aHaystack[index], aHaystack[index - 1], true) !== 0) {
break;
}
--index;
}
return index;
};