Protect base/numerics against change in intmax_t's underlying type

base/numerics/safe_math_impl.h

 // Copyright 2014 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.
 
 #ifndef BASE_NUMERICS_SAFE_MATH_IMPL_H_
 #define BASE_NUMERICS_SAFE_MATH_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 39 matching lines @@
 struct IntegerForSizeAndSign<4, false> {
   typedef uint32_t type;
 };
 template <>
 struct IntegerForSizeAndSign<8, true> {
   typedef int64_t type;
 };
 template <>
 struct IntegerForSizeAndSign<8, false> {
   typedef uint64_t type;
+  static_assert(sizeof(uintmax_t) == 8,

[Tom Sepez, 2016/11/17 17:04:54]

nit: Do you want a <= or >= comparison here?  Does the code break in both
directions?

[jschuh, 2016/11/17 18:06:46]

Good question. I can't really test, but I've seen enough implicit assumptions
that will break in the > case. And I figure it's safer to be strict than not,
assuming it makes it through the bots.

+                "Max integer size not supported for this toolchain.");
 };
 
 // WARNING: We have no IntegerForSizeAndSign<16, *>. If we ever add one to
 // support 128-bit math, then the ArithmeticPromotion template below will need
 // to be updated (or more likely replaced with a decltype expression).
 
 template <typename Integer>
 struct UnsignedIntegerForSize {
   typedef typename std::enable_if<
       std::numeric_limits<Integer>::is_integer,
@@ skipping 680 matching lines @@
       : value_(static_cast<T>(rhs.value())) {}
 
   bool is_valid() const { return std::isfinite(value_); }
   T value() const { return value_; }
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_MATH_IMPL_H_