Add numeric_cast for checked integral narrowing casts

base/safe_numerics_unittest.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <gtest/gtest.h>
+
+#include <vector>
+
+#include "base/safe_numerics.h"
+
+TEST(SafeNumerics, NumericCast) {

[darin (slow to review), 2013/01/15 18:53:29]

nit: put this TEST inside the base namespace so that you don't need to type
base:: everywhere.  if you follow my suggestion of putting IsValidNumericCast
into the base::internal:: namespace, then you could also put the TEST in the
base::internal:: namespace too or just add a using directive for
IsValidNumericCast.

[scottmg, 2013/01/15 19:30:17]

Done.

+  int small_positive = 1;
+  int small_negative = -1;
+  int large_positive = INT_MAX;
+  int large_negative = INT_MIN;
+
+  // Narrow signed destination.
+  EXPECT_TRUE(base::IsNumericCastableTo<signed char>(small_positive));
+  EXPECT_TRUE(base::IsNumericCastableTo<signed char>(small_negative));
+  EXPECT_FALSE(base::IsNumericCastableTo<signed char>(large_positive));
+  EXPECT_FALSE(base::IsNumericCastableTo<signed char>(large_negative));
+  EXPECT_TRUE(base::IsNumericCastableTo<signed short>(small_positive));
+  EXPECT_TRUE(base::IsNumericCastableTo<signed short>(small_negative));
+
+  // Narrow unsigned destination.
+  EXPECT_TRUE(base::IsNumericCastableTo<unsigned char>(small_positive));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned char>(small_negative));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned char>(large_positive));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned char>(large_negative));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned short>(small_negative));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned short>(large_negative));
+
+  // Same width signed destination.
+  EXPECT_TRUE(base::IsNumericCastableTo<signed int>(small_positive));
+  EXPECT_TRUE(base::IsNumericCastableTo<signed int>(small_negative));
+  EXPECT_TRUE(base::IsNumericCastableTo<signed int>(large_positive));
+  EXPECT_TRUE(base::IsNumericCastableTo<signed int>(large_negative));
+
+  // Same width unsigned destination.
+  EXPECT_TRUE(base::IsNumericCastableTo<unsigned int>(small_positive));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned int>(small_negative));
+  EXPECT_TRUE(base::IsNumericCastableTo<unsigned int>(large_positive));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned int>(large_negative));
+
+  // Wider signed destination.
+  EXPECT_TRUE(base::IsNumericCastableTo<long long>(small_positive));
+  EXPECT_TRUE(base::IsNumericCastableTo<long long>(large_negative));
+  EXPECT_TRUE(base::IsNumericCastableTo<long long>(small_positive));
+  EXPECT_TRUE(base::IsNumericCastableTo<long long>(large_negative));
+
+  // Wider unsigned destination.
+  EXPECT_TRUE(base::IsNumericCastableTo<unsigned long long>(small_positive));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned long long>(small_negative));
+  EXPECT_TRUE(base::IsNumericCastableTo<unsigned long long>(large_positive));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned long long>(large_negative));
+
+  // Negative to size_t.
+  EXPECT_FALSE(base::IsNumericCastableTo<size_t>(small_negative));
+  EXPECT_FALSE(base::IsNumericCastableTo<size_t>(large_negative));
+
+  // Various edge cases.
+  EXPECT_TRUE(base::IsNumericCastableTo<int>(static_cast<short>(SHRT_MIN)));
+  EXPECT_FALSE(
+      base::IsNumericCastableTo<unsigned short>(static_cast<short>(SHRT_MIN)));
+  EXPECT_FALSE(base::IsNumericCastableTo<unsigned short>(SHRT_MIN));
+
+  // These shouldn't compile.
+  // EXPECT_TRUE(base::IsNumericCastableTo<float>(0.0));

[darin (slow to review), 2013/01/15 18:53:29]

I think there is support for testing that certain code won't compile.  See
build/nocompile.gypi and base/bind_unittest.nc and base/callback_unittest.nc

[scottmg, 2013/01/15 19:30:17]

Looks like they've been disabled for a while unfortunately. :(
https://code.google.com/p/chromium/issues/detail?id=105388

Moved to base/safe_numerics_unittest.nc as examples anyway.

+  // EXPECT_TRUE(base::IsNumericCastableTo<double>(0.0f));
+  // EXPECT_FALSE(base::IsNumericCastableTo<int>(DBL_MAX));
+
+  // Confirm that numeric_cast<> actually compiles.
+  std::vector<int> v;
+  unsigned int checked_size = base::numeric_cast<unsigned int>(v.size());
+  EXPECT_EQ(0, checked_size);
+}