// 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_CONVERSIONS_H_
#define BASE_NUMERICS_SAFE_CONVERSIONS_H_

#include <stddef.h>

#include <cmath>
#include <limits>
#include <type_traits>

#include "anglebase/numerics/safe_conversions_impl.h"

#if defined(__ARMEL__) && !defined(__native_client__)
#    include "anglebase/numerics/safe_conversions_arm_impl.h"
#    define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (1)
#else
#    define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (0)
#endif

#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS
#    include <ostream>
#endif

namespace angle
{
namespace base
{
namespace internal
{

#if !BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
template <typename Dst, typename Src>
struct SaturateFastAsmOp
{
    static constexpr bool is_supported = false;
    static constexpr Dst Do(Src)
    {
        // Force a compile failure if instantiated.
        return CheckOnFailure::template HandleFailure<Dst>();
    }
};
#endif  // BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS
#undef BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS

// The following special case a few specific integer conversions where we can
// eke out better performance than range checking.
template <typename Dst, typename Src, typename Enable = void>
struct IsValueInRangeFastOp
{
    static constexpr bool is_supported = false;
    static constexpr bool Do(Src value)
    {
        // Force a compile failure if instantiated.
        return CheckOnFailure::template HandleFailure<bool>();
    }
};

// Signed to signed range comparison.
template <typename Dst, typename Src>
struct IsValueInRangeFastOp<
    Dst,
    Src,
    typename std::enable_if<std::is_integral<Dst>::value && std::is_integral<Src>::value &&
                            std::is_signed<Dst>::value && std::is_signed<Src>::value &&
                            !IsTypeInRangeForNumericType<Dst, Src>::value>::type>
{
    static constexpr bool is_supported = true;

    static constexpr bool Do(Src value)
    {
        // Just downcast to the smaller type, sign extend it back to the original
        // type, and then see if it matches the original value.
        return value == static_cast<Dst>(value);
    }
};

// Signed to unsigned range comparison.
template <typename Dst, typename Src>
struct IsValueInRangeFastOp<
    Dst,
    Src,
    typename std::enable_if<std::is_integral<Dst>::value && std::is_integral<Src>::value &&
                            !std::is_signed<Dst>::value && std::is_signed<Src>::value &&
                            !IsTypeInRangeForNumericType<Dst, Src>::value>::type>
{
    static constexpr bool is_supported = true;

    static constexpr bool Do(Src value)
    {
        // We cast a signed as unsigned to overflow negative values to the top,
        // then compare against whichever maximum is smaller, as our upper bound.
        return as_unsigned(value) <= as_unsigned(CommonMax<Src, Dst>());
    }
};

// Convenience function that returns true if the supplied value is in range
// for the destination type.
template <typename Dst, typename Src>
constexpr bool IsValueInRangeForNumericType(Src value)
{
    using SrcType = typename internal::UnderlyingType<Src>::type;
    return internal::IsValueInRangeFastOp<Dst, SrcType>::is_supported
               ? internal::IsValueInRangeFastOp<Dst, SrcType>::Do(static_cast<SrcType>(value))
               : internal::DstRangeRelationToSrcRange<Dst>(static_cast<SrcType>(value)).IsValid();
}

// checked_cast<> is analogous to static_cast<> for numeric types,
// except that it CHECKs that the specified numeric conversion will not
// overflow or underflow. NaN source will always trigger a CHECK.
template <typename Dst, class CheckHandler = internal::CheckOnFailure, typename Src>
constexpr Dst checked_cast(Src value)
{
    // This throws a compile-time error on evaluating the constexpr if it can be
    // determined at compile-time as failing, otherwise it will CHECK at runtime.
    using SrcType = typename internal::UnderlyingType<Src>::type;
    return BASE_NUMERICS_LIKELY((IsValueInRangeForNumericType<Dst>(value)))
               ? static_cast<Dst>(static_cast<SrcType>(value))
               : CheckHandler::template HandleFailure<Dst>();
}

// Default boundaries for integral/float: max/infinity, lowest/-infinity, 0/NaN.
// You may provide your own limits (e.g. to saturated_cast) so long as you
// implement all of the static constexpr member functions in the class below.
template <typename T>
struct SaturationDefaultLimits : public std::numeric_limits<T>
{
    static constexpr T NaN()
    {
        return std::numeric_limits<T>::has_quiet_NaN ? std::numeric_limits<T>::quiet_NaN() : T();
    }
    using std::numeric_limits<T>::max;
    static constexpr T Overflow()
    {
        return std::numeric_limits<T>::has_infinity ? std::numeric_limits<T>::infinity()
                                                    : std::numeric_limits<T>::max();
    }
    using std::numeric_limits<T>::lowest;
    static constexpr T Underflow()
    {
        return std::numeric_limits<T>::has_infinity ? std::numeric_limits<T>::infinity() * -1
                                                    : std::numeric_limits<T>::lowest();
    }
};

template <typename Dst, template <typename> class S, typename Src>
constexpr Dst saturated_cast_impl(Src value, RangeCheck constraint)
{
    // For some reason clang generates much better code when the branch is
    // structured exactly this way, rather than a sequence of checks.
    return !constraint.IsOverflowFlagSet()
               ? (!constraint.IsUnderflowFlagSet() ? static_cast<Dst>(value) : S<Dst>::Underflow())
               // Skip this check for integral Src, which cannot be NaN.
               : (std::is_integral<Src>::value || !constraint.IsUnderflowFlagSet()
                      ? S<Dst>::Overflow()
                      : S<Dst>::NaN());
}

// We can reduce the number of conditions and get slightly better performance
// for normal signed and unsigned integer ranges. And in the specific case of
// Arm, we can use the optimized saturation instructions.
template <typename Dst, typename Src, typename Enable = void>
struct SaturateFastOp
{
    static constexpr bool is_supported = false;
    static constexpr Dst Do(Src value)
    {
        // Force a compile failure if instantiated.
        return CheckOnFailure::template HandleFailure<Dst>();
    }
};

template <typename Dst, typename Src>
struct SaturateFastOp<
    Dst,
    Src,
    typename std::enable_if<std::is_integral<Src>::value && std::is_integral<Dst>::value &&
                            SaturateFastAsmOp<Dst, Src>::is_supported>::type>
{
    static constexpr bool is_supported = true;
    static constexpr Dst Do(Src value) { return SaturateFastAsmOp<Dst, Src>::Do(value); }
};

template <typename Dst, typename Src>
struct SaturateFastOp<
    Dst,
    Src,
    typename std::enable_if<std::is_integral<Src>::value && std::is_integral<Dst>::value &&
                            !SaturateFastAsmOp<Dst, Src>::is_supported>::type>
{
    static constexpr bool is_supported = true;
    static constexpr Dst Do(Src value)
    {
        // The exact order of the following is structured to hit the correct
        // optimization heuristics across compilers. Do not change without
        // checking the emitted code.
        const Dst saturated = CommonMaxOrMin<Dst, Src>(
            IsMaxInRangeForNumericType<Dst, Src>() ||
            (!IsMinInRangeForNumericType<Dst, Src>() && IsValueNegative(value)));
        return BASE_NUMERICS_LIKELY(IsValueInRangeForNumericType<Dst>(value))
                   ? static_cast<Dst>(value)
                   : saturated;
    }
};

// saturated_cast<> is analogous to static_cast<> for numeric types, except
// that the specified numeric conversion will saturate by default rather than
// overflow or underflow, and NaN assignment to an integral will return 0.
// All boundary condition behaviors can be overriden with a custom handler.
template <typename Dst,
          template <typename> class SaturationHandler = SaturationDefaultLimits,
          typename Src>
constexpr Dst saturated_cast(Src value)
{
    using SrcType = typename UnderlyingType<Src>::type;
    return !IsCompileTimeConstant(value) && SaturateFastOp<Dst, SrcType>::is_supported &&
                   std::is_same<SaturationHandler<Dst>, SaturationDefaultLimits<Dst>>::value
               ? SaturateFastOp<Dst, SrcType>::Do(static_cast<SrcType>(value))
               : saturated_cast_impl<Dst, SaturationHandler, SrcType>(
                     static_cast<SrcType>(value),
                     DstRangeRelationToSrcRange<Dst, SaturationHandler, SrcType>(
                         static_cast<SrcType>(value)));
}

// strict_cast<> is analogous to static_cast<> for numeric types, except that
// it will cause a compile failure if the destination type is not large enough
// to contain any value in the source type. It performs no runtime checking.
template <typename Dst, typename Src>
constexpr Dst strict_cast(Src value)
{
    using SrcType = typename UnderlyingType<Src>::type;
    static_assert(UnderlyingType<Src>::is_numeric, "Argument must be numeric.");
    static_assert(std::is_arithmetic<Dst>::value, "Result must be numeric.");

    // If you got here from a compiler error, it's because you tried to assign
    // from a source type to a destination type that has insufficient range.
    // The solution may be to change the destination type you're assigning to,
    // and use one large enough to represent the source.
    // Alternatively, you may be better served with the checked_cast<> or
    // saturated_cast<> template functions for your particular use case.
    static_assert(StaticDstRangeRelationToSrcRange<Dst, SrcType>::value == NUMERIC_RANGE_CONTAINED,
                  "The source type is out of range for the destination type. "
                  "Please see strict_cast<> comments for more information.");

    return static_cast<Dst>(static_cast<SrcType>(value));
}

// Some wrappers to statically check that a type is in range.
template <typename Dst, typename Src, class Enable = void>
struct IsNumericRangeContained
{
    static constexpr bool value = false;
};

template <typename Dst, typename Src>
struct IsNumericRangeContained<
    Dst,
    Src,
    typename std::enable_if<ArithmeticOrUnderlyingEnum<Dst>::value &&
                            ArithmeticOrUnderlyingEnum<Src>::value>::type>
{
    static constexpr bool value =
        StaticDstRangeRelationToSrcRange<Dst, Src>::value == NUMERIC_RANGE_CONTAINED;
};

// StrictNumeric implements compile time range checking between numeric types by
// wrapping assignment operations in a strict_cast. This class is intended to be
// used for function arguments and return types, to ensure the destination type
// can always contain the source type. This is essentially the same as enforcing
// -Wconversion in gcc and C4302 warnings on MSVC, but it can be applied
// incrementally at API boundaries, making it easier to convert code so that it
// compiles cleanly with truncation warnings enabled.
// This template should introduce no runtime overhead, but it also provides no
// runtime checking of any of the associated mathematical operations. Use
// CheckedNumeric for runtime range checks of the actual value being assigned.
template <typename T>
class StrictNumeric
{
  public:
    using type = T;

    constexpr StrictNumeric() : value_(0) {}

    // Copy constructor.
    template <typename Src>
    constexpr StrictNumeric(const StrictNumeric<Src> &rhs) : value_(strict_cast<T>(rhs.value_))
    {}

    // This is not an explicit constructor because we implicitly upgrade regular
    // numerics to StrictNumerics to make them easier to use.
    template <typename Src>
    constexpr StrictNumeric(Src value)  // NOLINT(runtime/explicit)
        : value_(strict_cast<T>(value))
    {}

    // If you got here from a compiler error, it's because you tried to assign
    // from a source type to a destination type that has insufficient range.
    // The solution may be to change the destination type you're assigning to,
    // and use one large enough to represent the source.
    // If you're assigning from a CheckedNumeric<> class, you may be able to use
    // the AssignIfValid() member function, specify a narrower destination type to
    // the member value functions (e.g. val.template ValueOrDie<Dst>()), use one
    // of the value helper functions (e.g. ValueOrDieForType<Dst>(val)).
    // If you've encountered an _ambiguous overload_ you can use a static_cast<>
    // to explicitly cast the result to the destination type.
    // If none of that works, you may be better served with the checked_cast<> or
    // saturated_cast<> template functions for your particular use case.
    template <typename Dst,
              typename std::enable_if<IsNumericRangeContained<Dst, T>::value>::type * = nullptr>
    constexpr operator Dst() const
    {
        return static_cast<typename ArithmeticOrUnderlyingEnum<Dst>::type>(value_);
    }

  private:
    const T value_;
};

// Convience wrapper returns a StrictNumeric from the provided arithmetic type.
template <typename T>
constexpr StrictNumeric<typename UnderlyingType<T>::type> MakeStrictNum(const T value)
{
    return value;
}

#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS
// Overload the ostream output operator to make logging work nicely.
template <typename T>
std::ostream &operator<<(std::ostream &os, const StrictNumeric<T> &value)
{
    os << static_cast<T>(value);
    return os;
}
#endif

#define BASE_NUMERIC_COMPARISON_OPERATORS(CLASS, NAME, OP)                                     \
    template <typename L, typename R,                                                          \
              typename std::enable_if<internal::Is##CLASS##Op<L, R>::value>::type * = nullptr> \
    constexpr bool operator OP(const L lhs, const R rhs)                                       \
    {                                                                                          \
        return SafeCompare<NAME, typename UnderlyingType<L>::type,                             \
                           typename UnderlyingType<R>::type>(lhs, rhs);                        \
    }

BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLess, <)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLessOrEqual, <=)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreater, >)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreaterOrEqual, >=)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsEqual, ==)
BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsNotEqual, !=)

}  // namespace internal

using internal::as_signed;
using internal::as_unsigned;
using internal::checked_cast;
using internal::IsTypeInRangeForNumericType;
using internal::IsValueInRangeForNumericType;
using internal::IsValueNegative;
using internal::MakeStrictNum;
using internal::SafeUnsignedAbs;
using internal::saturated_cast;
using internal::strict_cast;
using internal::StrictNumeric;

// Explicitly make a shorter size_t alias for convenience.
using SizeT = StrictNumeric<size_t>;

// floating -> integral conversions that saturate and thus can actually return
// an integral type.  In most cases, these should be preferred over the std::
// versions.
template <
    typename Dst = int,
    typename Src,
    typename = std::enable_if_t<std::is_integral<Dst>::value && std::is_floating_point<Src>::value>>
Dst ClampFloor(Src value)
{
    return saturated_cast<Dst>(std::floor(value));
}
template <
    typename Dst = int,
    typename Src,
    typename = std::enable_if_t<std::is_integral<Dst>::value && std::is_floating_point<Src>::value>>
Dst ClampCeil(Src value)
{
    return saturated_cast<Dst>(std::ceil(value));
}
template <
    typename Dst = int,
    typename Src,
    typename = std::enable_if_t<std::is_integral<Dst>::value && std::is_floating_point<Src>::value>>
Dst ClampRound(Src value)
{
    const Src rounded = (value >= 0.0f) ? std::floor(value + 0.5f) : std::ceil(value - 0.5f);
    return saturated_cast<Dst>(rounded);
}

}  // namespace base
}  // namespace angle

#endif  // BASE_NUMERICS_SAFE_CONVERSIONS_H_