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+/* -*- 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;
+};