Fix sort order of -0 in TypedArrays.

avp · facebook-github-bot · commit 30fd290bb205 · 2019-10-11T16:57:03.000-07:00
Summary:
TypedArray sorting must put `-0` before `+0`, so add a special check
for that.

Reviewed By: dulinriley

Differential Revision: D17632592

fbshipit-source-id: 97a966d2b196e629f4722f2831a14be5a0cb64d3
diff --git a/lib/VM/JSLib/TypedArray.cpp b/lib/VM/JSLib/TypedArray.cpp
@@ -323,7 +323,14 @@ class TypedArraySortModel : public SortModel {
     HermesValue aVal = JSObject::getOwnIndexed(*self_, runtime_, a);
     HermesValue bVal = JSObject::getOwnIndexed(*self_, runtime_, b);
     if (!WithCompareFn) {
-      return aVal.getNumber() < bVal.getNumber();
+      double a = aVal.getNumber();
+      double b = bVal.getNumber();
+      if (LLVM_UNLIKELY(a == 0) && LLVM_UNLIKELY(b == 0) &&
+          LLVM_UNLIKELY(std::signbit(a)) && LLVM_UNLIKELY(!std::signbit(b))) {
+        // -0 < +0, according to the spec.
+        return true;
+      }
+      return a < b;
     }
     assert(compareFn_ && "Cannot use this version if the compareFn is null");
     // ES7 22.2.3.26 2a.
diff --git a/test/hermes/TypedArray.js b/test/hermes/TypedArray.js
@@ -934,6 +934,14 @@ cons.forEach(function(ta) {
     });
   }, TypeError);
 });
+
+(function negativeZeroSort() {
+  var x = new Float64Array([+0, -0]);
+  x.sort();
+  assert.equal(1 / x[0], -Infinity);
+  assert.equal(1 / x[1], +Infinity);
+})();
+
 /// @}
 
 /// @name TypedArray.prototype.set
