Bug 1163328 - Add an And<...> class to TemplateLib.h which performs logical and on a variadic number of booleans known at compile time. r=froydnj

mfbt/TemplateLib.h

@@ -20,6 +20,8 @@
 #include <limits.h>
 #include <stddef.h>
 
+#include "mozilla/TypeTraits.h"
+
 namespace mozilla {
 
 namespace tl {
@@ -105,6 +107,25 @@ struct MulOverflowMask
 template<> struct MulOverflowMask<0> { /* Error */ };
 template<> struct MulOverflowMask<1> { static const size_t value = 0; };
 
+/**
+ * And<bool...> computes the logical 'and' of its argument booleans.
+ *
+ * Examples:
+ *   mozilla::t1::And<true, true>::value is true.
+ *   mozilla::t1::And<true, false>::value is false.
+ *   mozilla::t1::And<>::value is true.
+ */
+
+template<bool...>
+struct And;
+
+template<>
+struct And<> : public TrueType { };
+
+template<bool C1, bool... Cn>
+struct And<C1, Cn...>
+  : public Conditional<C1, And<Cn...>, FalseType>::Type { };
+
 } // namespace tl
 
 } // namespace mozilla

mfbt/tests/TestTemplateLib.cpp

@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/TemplateLib.h"
+
+using mozilla::tl::And;
+
+static_assert(And<>::value == true,
+              "And<>::value should be true");
+static_assert(And<true>::value == true,
+              "And<true>::value should be true");
+static_assert(And<false>::value == false,
+              "And<false>::value should be false");
+static_assert(And<false, true>::value == false,
+              "And<false, true>::value should be false");
+static_assert(And<false, false>::value == false,
+              "And<false, false>::value should be false");
+static_assert(And<true, false>::value == false,
+              "And<true, false>::value should be false");
+static_assert(And<true, true>::value == true,
+              "And<true, true>::value should be true");
+static_assert(And<true, true, true>::value == true,
+              "And<true, true, true>::value should be true");
+static_assert(And<true, false, true>::value == false,
+              "And<true, false, true>::value should be false");
+
+int
+main()
+{
+  // Nothing to do here.
+  return 0;
+}

mfbt/tests/moz.build

@@ -28,6 +28,7 @@ CppUnitTests([
     'TestSegmentedVector',
     'TestSHA1',
     'TestSplayTree',
+    'TestTemplateLib',
     'TestTypedEnum',
     'TestTypeTraits',
     'TestUniquePtr',