Expand support in safe_numeric.h

base/safe_numerics.h

-// Copyright 2013 The Chromium Authors. All rights reserved.
+// 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_SAFE_NUMERICS_H_
 #define BASE_SAFE_NUMERICS_H_
 
 #include <limits>
 
 #include "base/logging.h"
+#include "base/safe_numerics_impl.h"
 
 namespace base {
-namespace internal {
 
-template <bool SameSize, bool DestLarger,
-          bool DestIsSigned, bool SourceIsSigned>
-struct IsValidNumericCastImpl;
-
-#define BASE_NUMERIC_CAST_CASE_SPECIALIZATION(A, B, C, D, Code) \
-template <> struct IsValidNumericCastImpl<A, B, C, D> { \
-  template <class Source, class DestBounds> static inline bool Test( \
-      Source source, DestBounds min, DestBounds max) { \
-    return Code; \
-  } \
+// Convenience function that returns true if the supplied value is in range
+// for the destination type.
+template <class Dest, class Source>
+inline bool IsValueInRangeForNumericType(Source source) {
+  return internal::NumericRangeCheck<Dest>(source) == internal::TYPE_VALID;
 }
 
-#define BASE_NUMERIC_CAST_CASE_SAME_SIZE(DestSigned, SourceSigned, Code) \
-  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
-      true, true, DestSigned, SourceSigned, Code); \
-  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
-      true, false, DestSigned, SourceSigned, Code)
-
-#define BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(DestSigned, SourceSigned, Code) \
-  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
-      false, false, DestSigned, SourceSigned, Code); \
-
-#define BASE_NUMERIC_CAST_CASE_DEST_LARGER(DestSigned, SourceSigned, Code) \
-  BASE_NUMERIC_CAST_CASE_SPECIALIZATION( \
-      false, true, DestSigned, SourceSigned, Code); \
-
-// The three top level cases are:
-// - Same size
-// - Source larger
-// - Dest larger
-// And for each of those three cases, we handle the 4 different possibilities
-// of signed and unsigned. This gives 12 cases to handle, which we enumerate
-// below.
-//
-// The last argument in each of the macros is the actual comparison code. It
-// has three arguments available, source (the value), and min/max which are
-// the ranges of the destination.
-
-
-// These are the cases where both types have the same size.
-
-// Both signed.
-BASE_NUMERIC_CAST_CASE_SAME_SIZE(true, true, true);
-// Both unsigned.
-BASE_NUMERIC_CAST_CASE_SAME_SIZE(false, false, true);
-// Dest unsigned, Source signed.
-BASE_NUMERIC_CAST_CASE_SAME_SIZE(false, true, source >= 0);
-// Dest signed, Source unsigned.
-// This cast is OK because Dest's max must be less than Source's.
-BASE_NUMERIC_CAST_CASE_SAME_SIZE(true, false,
-                                 source <= static_cast<Source>(max));
-
-
-// These are the cases where Source is larger.
-
-// Both unsigned.
-BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(false, false, source <= max);
-// Both signed.
-BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(true, true,
-                                     source >= min && source <= max);
-// Dest is unsigned, Source is signed.
-BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(false, true,
-                                     source >= 0 && source <= max);
-// Dest is signed, Source is unsigned.
-// This cast is OK because Dest's max must be less than Source's.
-BASE_NUMERIC_CAST_CASE_SOURCE_LARGER(true, false,
-                                     source <= static_cast<Source>(max));
-
-
-// These are the cases where Dest is larger.
-
-// Both unsigned.
-BASE_NUMERIC_CAST_CASE_DEST_LARGER(false, false, true);
-// Both signed.
-BASE_NUMERIC_CAST_CASE_DEST_LARGER(true, true, true);
-// Dest is unsigned, Source is signed.
-BASE_NUMERIC_CAST_CASE_DEST_LARGER(false, true, source >= 0);
-// Dest is signed, Source is unsigned.
-BASE_NUMERIC_CAST_CASE_DEST_LARGER(true, false, true);
-
-#undef BASE_NUMERIC_CAST_CASE_SPECIALIZATION
-#undef BASE_NUMERIC_CAST_CASE_SAME_SIZE
-#undef BASE_NUMERIC_CAST_CASE_SOURCE_LARGER
-#undef BASE_NUMERIC_CAST_CASE_DEST_LARGER
-
-
-// The main test for whether the conversion will under or overflow.
-template <class Dest, class Source>
-inline bool IsValidNumericCast(Source source) {
-  typedef std::numeric_limits<Source> SourceLimits;
-  typedef std::numeric_limits<Dest> DestLimits;
-  COMPILE_ASSERT(SourceLimits::is_specialized, argument_must_be_numeric);
-  COMPILE_ASSERT(SourceLimits::is_integer, argument_must_be_integral);
-  COMPILE_ASSERT(DestLimits::is_specialized, result_must_be_numeric);
-  COMPILE_ASSERT(DestLimits::is_integer, result_must_be_integral);
-
-  return IsValidNumericCastImpl<
-      sizeof(Dest) == sizeof(Source),
-      (sizeof(Dest) > sizeof(Source)),
-      DestLimits::is_signed,
-      SourceLimits::is_signed>::Test(
-          source,
-          DestLimits::min(),
-          DestLimits::max());
-}
-
-}  // namespace internal
-
 // checked_numeric_cast<> is analogous to static_cast<> for numeric types,
 // except that it CHECKs that the specified numeric conversion will not
-// overflow or underflow. Floating point arguments are not currently allowed
-// (this is COMPILE_ASSERTd), though this could be supported if necessary.
+// overflow or underflow. Floating point arguments are allowed only as a
+// source because they already have well defined saturation semantics.
+// NaN source will always trigger a CHECK.
 template <class Dest, class Source>
 inline Dest checked_numeric_cast(Source source) {
-  CHECK(internal::IsValidNumericCast<Dest>(source));
+  CHECK(IsValueInRangeForNumericType<Dest>(source));
   return static_cast<Dest>(source);
 }
 
+// saturated_cast<> is analogous to static_cast<> for numeric types, except
+// that the specified numeric conversion will saturate rather than overflow or
+// underflow. Floating point arguments are allowed only as a source because
+// they already have well defined saturation semantics. NaN source will force a
+// CHECK condition.
+template <class Dest, class Source>
+inline Dest saturated_cast(Source source) {
+  switch (internal::NumericRangeCheck<Dest>(source)) {
+    case internal::TYPE_UNDERFLOW:
+      return std::numeric_limits<Dest>::min();
+
+    case internal::TYPE_OVERFLOW:
+      return std::numeric_limits<Dest>::max();
+
+    // Should fail only on attempting to assign NaN to a saturated integer.
+    case internal::TYPE_INVALID:
+      CHECK(false);
+      return std::numeric_limits<Dest>::max();
+
+    default:
+      return static_cast<Dest>(source);
+  }
+}
+
 }  // namespace base
 
 #endif  // BASE_SAFE_NUMERICS_H_