// Copyright 2017 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_CLAMPED_MATH_IMPL_H_
#define BASE_NUMERICS_CLAMPED_MATH_IMPL_H_

#include <stddef.h>
#include <stdint.h>

#include <climits>
#include <cmath>
#include <cstdlib>
#include <limits>
#include <type_traits>

#include "anglebase/numerics/checked_math.h"
#include "anglebase/numerics/safe_conversions.h"
#include "anglebase/numerics/safe_math_shared_impl.h"

namespace angle
{
namespace base
{
namespace internal
{

template <typename T,
          typename std::enable_if<std::is_integral<T>::value && std::is_signed<T>::value>::type * =
              nullptr>
constexpr T SaturatedNegWrapper(T value)
{
    return MustTreatAsConstexpr(value) || !ClampedNegFastOp<T>::is_supported
               ? (NegateWrapper(value) != std::numeric_limits<T>::lowest()
                      ? NegateWrapper(value)
                      : std::numeric_limits<T>::max())
               : ClampedNegFastOp<T>::Do(value);
}

template <typename T,
          typename std::enable_if<std::is_integral<T>::value && !std::is_signed<T>::value>::type * =
              nullptr>
constexpr T SaturatedNegWrapper(T value)
{
    return T(0);
}

template <typename T, typename std::enable_if<std::is_floating_point<T>::value>::type * = nullptr>
constexpr T SaturatedNegWrapper(T value)
{
    return -value;
}

template <typename T, typename std::enable_if<std::is_integral<T>::value>::type * = nullptr>
constexpr T SaturatedAbsWrapper(T value)
{
    // The calculation below is a static identity for unsigned types, but for
    // signed integer types it provides a non-branching, saturated absolute value.
    // This works because SafeUnsignedAbs() returns an unsigned type, which can
    // represent the absolute value of all negative numbers of an equal-width
    // integer type. The call to IsValueNegative() then detects overflow in the
    // special case of numeric_limits<T>::min(), by evaluating the bit pattern as
    // a signed integer value. If it is the overflow case, we end up subtracting
    // one from the unsigned result, thus saturating to numeric_limits<T>::max().
    return static_cast<T>(SafeUnsignedAbs(value) - IsValueNegative<T>(SafeUnsignedAbs(value)));
}

template <typename T, typename std::enable_if<std::is_floating_point<T>::value>::type * = nullptr>
constexpr T SaturatedAbsWrapper(T value)
{
    return value < 0 ? -value : value;
}

template <typename T, typename U, class Enable = void>
struct ClampedAddOp
{};

template <typename T, typename U>
struct ClampedAddOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type = typename MaxExponentPromotion<T, U>::type;
    template <typename V = result_type>
    static constexpr V Do(T x, U y)
    {
        if (ClampedAddFastOp<T, U>::is_supported)
            return ClampedAddFastOp<T, U>::template Do<V>(x, y);

        static_assert(
            std::is_same<V, result_type>::value || IsTypeInRangeForNumericType<U, V>::value,
            "The saturation result cannot be determined from the "
            "provided types.");
        const V saturated = CommonMaxOrMin<V>(IsValueNegative(y));
        V result          = {};
        return BASE_NUMERICS_LIKELY((CheckedAddOp<T, U>::Do(x, y, &result))) ? result : saturated;
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedSubOp
{};

template <typename T, typename U>
struct ClampedSubOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type = typename MaxExponentPromotion<T, U>::type;
    template <typename V = result_type>
    static constexpr V Do(T x, U y)
    {
        if constexpr (ClampedSubFastOp<T, U>::is_supported)
            return ClampedSubFastOp<T, U>::template Do<V>(x, y);

        static_assert(
            std::is_same<V, result_type>::value || IsTypeInRangeForNumericType<U, V>::value,
            "The saturation result cannot be determined from the "
            "provided types.");
        const V saturated = CommonMaxOrMin<V>(!IsValueNegative(y));
        V result          = {};
        return BASE_NUMERICS_LIKELY((CheckedSubOp<T, U>::Do(x, y, &result))) ? result : saturated;
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedMulOp
{};

template <typename T, typename U>
struct ClampedMulOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type = typename MaxExponentPromotion<T, U>::type;
    template <typename V = result_type>
    static constexpr V Do(T x, U y)
    {
        if constexpr (ClampedMulFastOp<T, U>::is_supported)
            return ClampedMulFastOp<T, U>::template Do<V>(x, y);

        V result          = {};
        const V saturated = CommonMaxOrMin<V>(IsValueNegative(x) ^ IsValueNegative(y));
        return BASE_NUMERICS_LIKELY((CheckedMulOp<T, U>::Do(x, y, &result))) ? result : saturated;
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedDivOp
{};

template <typename T, typename U>
struct ClampedDivOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type = typename MaxExponentPromotion<T, U>::type;
    template <typename V = result_type>
    static constexpr V Do(T x, U y)
    {
        V result = {};
        if (BASE_NUMERICS_LIKELY((CheckedDivOp<T, U>::Do(x, y, &result))))
            return result;
        // Saturation goes to max, min, or NaN (if x is zero).
        return x ? CommonMaxOrMin<V>(IsValueNegative(x) ^ IsValueNegative(y))
                 : SaturationDefaultLimits<V>::NaN();
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedModOp
{};

template <typename T, typename U>
struct ClampedModOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type = typename MaxExponentPromotion<T, U>::type;
    template <typename V = result_type>
    static constexpr V Do(T x, U y)
    {
        V result = {};
        return BASE_NUMERICS_LIKELY((CheckedModOp<T, U>::Do(x, y, &result))) ? result : x;
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedLshOp
{};

// Left shift. Non-zero values saturate in the direction of the sign. A zero
// shifted by any value always results in zero.
template <typename T, typename U>
struct ClampedLshOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type = T;
    template <typename V = result_type>
    static constexpr V Do(T x, U shift)
    {
        static_assert(!std::is_signed<U>::value, "Shift value must be unsigned.");
        if (BASE_NUMERICS_LIKELY(shift < std::numeric_limits<T>::digits))
        {
            // Shift as unsigned to avoid undefined behavior.
            V result = static_cast<V>(as_unsigned(x) << shift);
            // If the shift can be reversed, we know it was valid.
            if (BASE_NUMERICS_LIKELY(result >> shift == x))
                return result;
        }
        return x ? CommonMaxOrMin<V>(IsValueNegative(x)) : 0;
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedRshOp
{};

// Right shift. Negative values saturate to -1. Positive or 0 saturates to 0.
template <typename T, typename U>
struct ClampedRshOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type = T;
    template <typename V = result_type>
    static constexpr V Do(T x, U shift)
    {
        static_assert(!std::is_signed<U>::value, "Shift value must be unsigned.");
        // Signed right shift is odd, because it saturates to -1 or 0.
        const V saturated = as_unsigned(V(0)) - IsValueNegative(x);
        return BASE_NUMERICS_LIKELY(shift < IntegerBitsPlusSign<T>::value)
                   ? saturated_cast<V>(x >> shift)
                   : saturated;
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedAndOp
{};

template <typename T, typename U>
struct ClampedAndOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type =
        typename std::make_unsigned<typename MaxExponentPromotion<T, U>::type>::type;
    template <typename V>
    static constexpr V Do(T x, U y)
    {
        return static_cast<result_type>(x) & static_cast<result_type>(y);
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedOrOp
{};

// For simplicity we promote to unsigned integers.
template <typename T, typename U>
struct ClampedOrOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type =
        typename std::make_unsigned<typename MaxExponentPromotion<T, U>::type>::type;
    template <typename V>
    static constexpr V Do(T x, U y)
    {
        return static_cast<result_type>(x) | static_cast<result_type>(y);
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedXorOp
{};

// For simplicity we support only unsigned integers.
template <typename T, typename U>
struct ClampedXorOp<
    T,
    U,
    typename std::enable_if<std::is_integral<T>::value && std::is_integral<U>::value>::type>
{
    using result_type =
        typename std::make_unsigned<typename MaxExponentPromotion<T, U>::type>::type;
    template <typename V>
    static constexpr V Do(T x, U y)
    {
        return static_cast<result_type>(x) ^ static_cast<result_type>(y);
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedMaxOp
{};

template <typename T, typename U>
struct ClampedMaxOp<
    T,
    U,
    typename std::enable_if<std::is_arithmetic<T>::value && std::is_arithmetic<U>::value>::type>
{
    using result_type = typename MaxExponentPromotion<T, U>::type;
    template <typename V = result_type>
    static constexpr V Do(T x, U y)
    {
        return IsGreater<T, U>::Test(x, y) ? saturated_cast<V>(x) : saturated_cast<V>(y);
    }
};

template <typename T, typename U, class Enable = void>
struct ClampedMinOp
{};

template <typename T, typename U>
struct ClampedMinOp<
    T,
    U,
    typename std::enable_if<std::is_arithmetic<T>::value && std::is_arithmetic<U>::value>::type>
{
    using result_type = typename LowestValuePromotion<T, U>::type;
    template <typename V = result_type>
    static constexpr V Do(T x, U y)
    {
        return IsLess<T, U>::Test(x, y) ? saturated_cast<V>(x) : saturated_cast<V>(y);
    }
};

// This is just boilerplate that wraps the standard floating point arithmetic.
// A macro isn't the nicest solution, but it beats rewriting these repeatedly.
#define BASE_FLOAT_ARITHMETIC_OPS(NAME, OP)                                                   \
    template <typename T, typename U>                                                         \
    struct Clamped##NAME##Op<T, U,                                                            \
                             typename std::enable_if<std::is_floating_point<T>::value ||      \
                                                     std::is_floating_point<U>::value>::type> \
    {                                                                                         \
        using result_type = typename MaxExponentPromotion<T, U>::type;                        \
        template <typename V = result_type>                                                   \
        static constexpr V Do(T x, U y)                                                       \
        {                                                                                     \
            return saturated_cast<V>(x OP y);                                                 \
        }                                                                                     \
    };

BASE_FLOAT_ARITHMETIC_OPS(Add, +)
BASE_FLOAT_ARITHMETIC_OPS(Sub, -)
BASE_FLOAT_ARITHMETIC_OPS(Mul, *)
BASE_FLOAT_ARITHMETIC_OPS(Div, /)

#undef BASE_FLOAT_ARITHMETIC_OPS

}  // namespace internal
}  // namespace base
}  // namespace angle

#endif  // BASE_NUMERICS_CLAMPED_MATH_IMPL_H_