Refactor base/safe_numerics.h

base/safe_numerics_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_SAFE_NUMERICS_IMPL_H_
-#define BASE_SAFE_NUMERICS_IMPL_H_
-
-#include <limits>
-
-#include "base/macros.h"
-
-namespace base {
-namespace internal {
-
-enum DstSign {
-  DST_UNSIGNED,
-  DST_SIGNED
-};
-
-enum SrcSign {
-  SRC_UNSIGNED,
-  SRC_SIGNED
-};
-
-enum DstRange {
-  OVERLAPS_RANGE,
-  CONTAINS_RANGE
-};
-
-// Helper templates to statically determine if our destination type can contain
-// all values represented by the source type.
-
-template <typename Dst, typename Src,
-          DstSign IsDstSigned = std::numeric_limits<Dst>::is_signed ?
-                                DST_SIGNED : DST_UNSIGNED,
-          SrcSign IsSrcSigned = std::numeric_limits<Src>::is_signed ?
-                                SRC_SIGNED : SRC_UNSIGNED>
-struct StaticRangeCheck {};
-
-template <typename Dst, typename Src>
-struct StaticRangeCheck<Dst, Src, DST_SIGNED, SRC_SIGNED> {
-  typedef std::numeric_limits<Dst> DstLimits;
-  typedef std::numeric_limits<Src> SrcLimits;
-  // Compare based on max_exponent, which we must compute for integrals.
-  static const size_t kDstMaxExponent = DstLimits::is_iec559 ?
-                                        DstLimits::max_exponent :
-                                        (sizeof(Dst) * 8 - 1);
-  static const size_t kSrcMaxExponent = SrcLimits::is_iec559 ?
-                                        SrcLimits::max_exponent :
-                                        (sizeof(Src) * 8 - 1);
-  static const DstRange value = kDstMaxExponent >= kSrcMaxExponent ?
-                                CONTAINS_RANGE : OVERLAPS_RANGE;
-};
-
-template <typename Dst, typename Src>
-struct StaticRangeCheck<Dst, Src, DST_UNSIGNED, SRC_UNSIGNED> {
-  static const DstRange value = sizeof(Dst) >= sizeof(Src) ?
-                                CONTAINS_RANGE : OVERLAPS_RANGE;
-};
-
-template <typename Dst, typename Src>
-struct StaticRangeCheck<Dst, Src, DST_SIGNED, SRC_UNSIGNED> {
-  typedef std::numeric_limits<Dst> DstLimits;
-  typedef std::numeric_limits<Src> SrcLimits;
-  // Compare based on max_exponent, which we must compute for integrals.
-  static const size_t kDstMaxExponent = DstLimits::is_iec559 ?
-                                        DstLimits::max_exponent :
-                                        (sizeof(Dst) * 8 - 1);
-  static const size_t kSrcMaxExponent = sizeof(Src) * 8;
-  static const DstRange value = kDstMaxExponent >= kSrcMaxExponent ?
-                                CONTAINS_RANGE : OVERLAPS_RANGE;
-};
-
-template <typename Dst, typename Src>
-struct StaticRangeCheck<Dst, Src, DST_UNSIGNED, SRC_SIGNED> {
-  static const DstRange value = OVERLAPS_RANGE;
-};
-
-
-enum RangeCheckResult {
-  TYPE_VALID = 0,      // Value can be represented by the destination type.
-  TYPE_UNDERFLOW = 1,  // Value would overflow.
-  TYPE_OVERFLOW = 2,   // Value would underflow.
-  TYPE_INVALID = 3     // Source value is invalid (i.e. NaN).
-};
-
-// This macro creates a RangeCheckResult from an upper and lower bound
-// check by taking advantage of the fact that only NaN can be out of range in
-// both directions at once.
-#define BASE_NUMERIC_RANGE_CHECK_RESULT(is_in_upper_bound, is_in_lower_bound) \
-    RangeCheckResult(((is_in_upper_bound) ? 0 : TYPE_OVERFLOW) | \
-                            ((is_in_lower_bound) ? 0 : TYPE_UNDERFLOW))
-
-template <typename Dst,
-          typename Src,
-          DstSign IsDstSigned = std::numeric_limits<Dst>::is_signed ?
-                                DST_SIGNED : DST_UNSIGNED,
-          SrcSign IsSrcSigned = std::numeric_limits<Src>::is_signed ?
-                                SRC_SIGNED : SRC_UNSIGNED,
-          DstRange IsSrcRangeContained = StaticRangeCheck<Dst, Src>::value>
-struct RangeCheckImpl {};
-
-// The following templates are for ranges that must be verified at runtime. We
-// split it into checks based on signedness to avoid confusing casts and
-// compiler warnings on signed an unsigned comparisons.
-
-// Dst range always contains the result: nothing to check.
-template <typename Dst, typename Src, DstSign IsDstSigned, SrcSign IsSrcSigned>
-struct RangeCheckImpl<Dst, Src, IsDstSigned, IsSrcSigned, CONTAINS_RANGE> {
-  static RangeCheckResult Check(Src value) {
-    return TYPE_VALID;
-  }
-};
-
-// Signed to signed narrowing.
-template <typename Dst, typename Src>
-struct RangeCheckImpl<Dst, Src, DST_SIGNED, SRC_SIGNED, OVERLAPS_RANGE> {
-  static RangeCheckResult Check(Src value) {
-    typedef std::numeric_limits<Dst> DstLimits;
-    return DstLimits::is_iec559 ?
-           BASE_NUMERIC_RANGE_CHECK_RESULT(
-               value <= static_cast<Src>(DstLimits::max()),
-               value >= static_cast<Src>(DstLimits::max() * -1)) :
-           BASE_NUMERIC_RANGE_CHECK_RESULT(
-               value <= static_cast<Src>(DstLimits::max()),
-               value >= static_cast<Src>(DstLimits::min()));
-  }
-};
-
-// Unsigned to unsigned narrowing.
-template <typename Dst, typename Src>
-struct RangeCheckImpl<Dst, Src, DST_UNSIGNED, SRC_UNSIGNED, OVERLAPS_RANGE> {
-  static RangeCheckResult Check(Src value) {
-    typedef std::numeric_limits<Dst> DstLimits;
-    return BASE_NUMERIC_RANGE_CHECK_RESULT(
-               value <= static_cast<Src>(DstLimits::max()), true);
-  }
-};
-
-// Unsigned to signed.
-template <typename Dst, typename Src>
-struct RangeCheckImpl<Dst, Src, DST_SIGNED, SRC_UNSIGNED, OVERLAPS_RANGE> {
-  static RangeCheckResult Check(Src value) {
-    typedef std::numeric_limits<Dst> DstLimits;
-    return sizeof(Dst) > sizeof(Src) ? TYPE_VALID :
-           BASE_NUMERIC_RANGE_CHECK_RESULT(
-               value <= static_cast<Src>(DstLimits::max()), true);
-  }
-};
-
-// Signed to unsigned.
-template <typename Dst, typename Src>
-struct RangeCheckImpl<Dst, Src, DST_UNSIGNED, SRC_SIGNED, OVERLAPS_RANGE> {
-  static RangeCheckResult Check(Src value) {
-    typedef std::numeric_limits<Dst> DstLimits;
-    typedef std::numeric_limits<Src> SrcLimits;
-    // Compare based on max_exponent, which we must compute for integrals.
-    static const size_t kDstMaxExponent = sizeof(Dst) * 8;
-    static const size_t kSrcMaxExponent = SrcLimits::is_iec559 ?
-                                          SrcLimits::max_exponent :
-                                          (sizeof(Src) * 8 - 1);
-    return (kDstMaxExponent >= kSrcMaxExponent) ?
-           BASE_NUMERIC_RANGE_CHECK_RESULT(true, value >= static_cast<Src>(0)) :
-           BASE_NUMERIC_RANGE_CHECK_RESULT(
-               value <= static_cast<Src>(DstLimits::max()),
-               value >= static_cast<Src>(0));
-  }
-};
-
-template <typename Dst, typename Src>
-inline RangeCheckResult RangeCheck(Src value) {
-  COMPILE_ASSERT(std::numeric_limits<Src>::is_specialized,
-                 argument_must_be_numeric);
-  COMPILE_ASSERT(std::numeric_limits<Dst>::is_specialized,
-                 result_must_be_numeric);
-  return RangeCheckImpl<Dst, Src>::Check(value);
-}
-
-}  // namespace internal
-}  // namespace base
-
-#endif  // BASE_SAFE_NUMERICS_IMPL_H_
-