Add support for CheckedNumeric Max and Min constexpr functions

This also adds variadic helper functions CheckMax and CheckMin that
return the maximum or minimum (respectively) result of an arbitrary
number of arithmetic, CheckedNumeric, or StrictNumeric arguments.

Review-Url: https://codereview.chromium.org/2545253002
Cr-Commit-Position: refs/heads/master@{#436190}

diff --git a/base/numerics/safe_numerics_unittest.cc b/base/numerics/safe_numerics_unittest.cc
index f1522ba..7d42a83 100644
--- a/base/numerics/safe_numerics_unittest.cc
+++ b/base/numerics/safe_numerics_unittest.cc

@@ -26,6 +26,8 @@
 using base::ValueOrDieForType;
 using base::ValueOrDefaultForType;
 using base::CheckNum;
+using base::CheckMax;
+using base::CheckMin;
 using base::CheckAdd;
 using base::CheckSub;
 using base::CheckMul;
@@ -38,9 +40,9 @@
 using base::IsValueNegative;
 using base::SizeT;
 using base::StrictNumeric;
+using base::MakeStrictNum;
 using base::saturated_cast;
 using base::strict_cast;
-using base::StrictNumeric;
 using base::internal::MaxExponent;
 using base::internal::RANGE_VALID;
 using base::internal::RANGE_INVALID;
@@ -438,37 +440,63 @@
 void TestStrictComparison() {
   typedef numeric_limits<Dst> DstLimits;
   typedef numeric_limits<Src> SrcLimits;
-  static_assert(StrictNumeric<Src>(SrcLimits::min()) < DstLimits::max(), "");
-  static_assert(StrictNumeric<Src>(SrcLimits::min()) < SrcLimits::max(), "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::min()) >= DstLimits::max()),
+  static_assert(StrictNumeric<Src>(SrcLimits::lowest()) < DstLimits::max(), "");
+  static_assert(StrictNumeric<Src>(SrcLimits::lowest()) < SrcLimits::max(), "");
+  static_assert(!(StrictNumeric<Src>(SrcLimits::lowest()) >= DstLimits::max()),
                 "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::min()) >= SrcLimits::max()),
+  static_assert(!(StrictNumeric<Src>(SrcLimits::lowest()) >= SrcLimits::max()),
                 "");
-  static_assert(StrictNumeric<Src>(SrcLimits::min()) <= DstLimits::max(), "");
-  static_assert(StrictNumeric<Src>(SrcLimits::min()) <= SrcLimits::max(), "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::min()) > DstLimits::max()), "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::min()) > SrcLimits::max()), "");
-  static_assert(StrictNumeric<Src>(SrcLimits::max()) > DstLimits::min(), "");
-  static_assert(StrictNumeric<Src>(SrcLimits::max()) > SrcLimits::min(), "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) <= DstLimits::min()),
+  static_assert(StrictNumeric<Src>(SrcLimits::lowest()) <= DstLimits::max(),
                 "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) <= SrcLimits::min()),
+  static_assert(StrictNumeric<Src>(SrcLimits::lowest()) <= SrcLimits::max(),
                 "");
-  static_assert(StrictNumeric<Src>(SrcLimits::max()) >= DstLimits::min(), "");
-  static_assert(StrictNumeric<Src>(SrcLimits::max()) >= SrcLimits::min(), "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) < DstLimits::min()), "");
-  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) < SrcLimits::min()), "");
+  static_assert(!(StrictNumeric<Src>(SrcLimits::lowest()) > DstLimits::max()),
+                "");
+  static_assert(!(StrictNumeric<Src>(SrcLimits::lowest()) > SrcLimits::max()),
+                "");
+  static_assert(StrictNumeric<Src>(SrcLimits::max()) > DstLimits::lowest(), "");
+  static_assert(StrictNumeric<Src>(SrcLimits::max()) > SrcLimits::lowest(), "");
+  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) <= DstLimits::lowest()),
+                "");
+  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) <= SrcLimits::lowest()),
+                "");
+  static_assert(StrictNumeric<Src>(SrcLimits::max()) >= DstLimits::lowest(),
+                "");
+  static_assert(StrictNumeric<Src>(SrcLimits::max()) >= SrcLimits::lowest(),
+                "");
+  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) < DstLimits::lowest()),
+                "");
+  static_assert(!(StrictNumeric<Src>(SrcLimits::max()) < SrcLimits::lowest()),
+                "");
   static_assert(StrictNumeric<Src>(static_cast<Src>(1)) == static_cast<Dst>(1),
                 "");
   static_assert(StrictNumeric<Src>(static_cast<Src>(1)) != static_cast<Dst>(0),
                 "");
   static_assert(StrictNumeric<Src>(SrcLimits::max()) != static_cast<Dst>(0),
                 "");
-  static_assert(StrictNumeric<Src>(SrcLimits::max()) != DstLimits::min(), "");
+  static_assert(StrictNumeric<Src>(SrcLimits::max()) != DstLimits::lowest(),
+                "");
   static_assert(
       !(StrictNumeric<Src>(static_cast<Src>(1)) != static_cast<Dst>(1)), "");
   static_assert(
       !(StrictNumeric<Src>(static_cast<Src>(1)) == static_cast<Dst>(0)), "");
+
+  // Due to differences in float handling between compilers, these aren't
+  // compile-time constants everywhere. So, we use run-time tests.
+  EXPECT_EQ(SrcLimits::max(),
+            CheckNum(SrcLimits::max()).Max(DstLimits::lowest()).ValueOrDie());
+  EXPECT_EQ(DstLimits::max(),
+            CheckNum(SrcLimits::lowest()).Max(DstLimits::max()).ValueOrDie());
+  EXPECT_EQ(DstLimits::lowest(),
+            CheckNum(SrcLimits::max()).Min(DstLimits::lowest()).ValueOrDie());
+  EXPECT_EQ(SrcLimits::lowest(),
+            CheckNum(SrcLimits::lowest()).Min(DstLimits::max()).ValueOrDie());
+  EXPECT_EQ(SrcLimits::lowest(), CheckMin(MakeStrictNum(1), CheckNum(0),
+                                          DstLimits::max(), SrcLimits::lowest())
+                                     .ValueOrDie());
+  EXPECT_EQ(DstLimits::max(), CheckMax(MakeStrictNum(1), CheckNum(0),
+                                       DstLimits::max(), SrcLimits::lowest())
+                                  .ValueOrDie());
 }
 
 template <typename Dst, typename Src>