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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;
+};