originalPositionFor() API fix for indexed maps: faster due to not executing a useless=buggy comparison near the end in binary search

lib/binary-search.js

@@ -32,7 +32,7 @@ function recursiveSearch(aLow, aHigh, aNeedle, aHaystack, aCompare, aBias) {
   //   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.
   const mid = Math.floor((aHigh - aLow) / 2) + aLow;
-  const cmp = aCompare(aNeedle, aHaystack[mid], true);
+  const cmp = aCompare(aNeedle, aHaystack[mid]);
   if (cmp === 0) {
     // Found the element we are looking for.
     return mid;
@@ -95,9 +95,10 @@ exports.search = function search(aNeedle, aHaystack, aCompare, aBias) {
 
   // 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.
+  // element ONLY IFF we found an exact match. 
+  // Make sure we always return the smallest of these.
   while (index - 1 >= 0) {
-    if (aCompare(aHaystack[index], aHaystack[index - 1], true) !== 0) {
+    if (aCompare(aNeedle, aHaystack[index - 1]) !== 0) {
       break;
     }
     --index;

test/test-binary-search.js

@@ -94,3 +94,29 @@ exports["test multiple matches at the beginning"] = function(assert) {
   assert.equal(binarySearch.search(needle, haystack, numberCompare,
                                    binarySearch.LEAST_UPPER_BOUND), 0);
 };
+
+exports["test fuzzy match with duplicates in the data at match point"] = function(assert) {
+  const needle = 2;
+  const haystack = [1, 1, 5, 5, 5, 5, 13, 21];
+
+  assert.equal(
+    binarySearch.search(
+      needle,
+      haystack,
+      numberCompare,
+      binarySearch.LEAST_UPPER_BOUND
+    ),
+    2
+  );
+
+  assert.equal(
+    binarySearch.search(
+      needle,
+      haystack,
+      numberCompare,
+      binarySearch.GREATEST_LOWER_BOUND
+    ),
+    1
+  );
+};
+