/*******************************************************************************
 *
 * MIT License
 *
 * Copyright (c) 2023 Advanced Micro Devices, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 *all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 *******************************************************************************/
// #include <miopen/bfloat16.hpp>
// #include <half.hpp>

#include "miopen_cstdint.hpp"
#include "miopen_type_traits.hpp"

namespace miopen_hip_f8_impl {

#ifndef __HIP_PLATFORM_AMD__
using hip_bfloat16 = bfloat16;
using half         = half_float::half;
#endif

enum class BitOp
{
    Equal, // sizeof(To) == sizeof(From)
    Widen, // sizeof(To) >  sizeof(From)
    Narrow // sizeof(To) <  sizeof(From)
};

template <class To, class From, BitOp Op>
MIOPEN_HIP_HOST_DEVICE To bit_copy(const From& src)
{
    static_assert(std::is_trivially_copyable_v<From> && std::is_trivially_copyable_v<To>,
                  "Requires trivially copyable types");

    if constexpr(Op == BitOp::Equal)
    {
        static_assert(sizeof(To) == sizeof(From), "BitOp::Equal requires equal sizes");
        To dst;
        __builtin_memcpy(&dst, &src, sizeof(To));
        return dst;
    }
    else if constexpr(Op == BitOp::Widen)
    {
        static_assert(sizeof(From) <= sizeof(To), "BitOp::Widen requires From <= To");
        To dst{}; // extra bytes are zeroed
        __builtin_memcpy(&dst, &src, sizeof(From));
        return dst;
    }
    else
    { // BitOp::Narrow
        static_assert(sizeof(From) >= sizeof(To), "BitOp::Narrow requires From >= To");
        To dst; // only low sizeof(To) bytes are written
        __builtin_memcpy(&dst, &src, sizeof(To));
        return dst;
    }
}

template <class To, class From>
MIOPEN_HIP_HOST_DEVICE To miopen_bit_cast(const From& src)
{
    if constexpr(sizeof(To) == sizeof(From))
        return bit_copy<To, From, BitOp::Equal>(src);
    else if constexpr(sizeof(To) > sizeof(From))
        return bit_copy<To, From, BitOp::Widen>(src);
    else
        return bit_copy<To, From, BitOp::Narrow>(src);
}

template <int wm, int we, typename T>
MIOPEN_HIP_HOST_DEVICE uint8_t cast_to_f8_no_range_reduce(T _x,
                                                          bool stoch   = false,
                                                          uint32_t rng = 0)
{
    static_assert(we == 5, "we==5");
    static_assert(sizeof(T) == 2, "no_range_reduce only works for float16");

    uint32_t x = miopen_bit_cast<uint16_t>(_x);
    uint32_t head, mantissa, exponent;
    uint32_t sign;

    const int mfmt      = 10;
    head                = x & 0xFC00;
    mantissa            = x & 0x3FF;
    exponent            = (head >> 10) & 0x1F;
    sign                = head >> 15;
    uint32_t signed_inf = (sign << 7) + (((1 << we) - 1) << wm);

    if((x & 0x7FFF) == 0x7C00)
        return signed_inf;
    if((x & 0x7C00) == 0x7C00)
        return signed_inf + 1;
    if(x == 0)
        return 0;
    if(x == 0x8000)
        return 0x80;

    //  uint32_t nextbit = 1<<(mfmt-wm-1);
    uint32_t drop_mask = (1 << (mfmt - wm)) - 1;

    // const int max_exp = (1<<we)-(negative_zero_nan ? 1 : 2);
    mantissa += (stoch ? rng : mantissa) & drop_mask;
    if(exponent != 0)
        mantissa += 1 << mfmt;
    if(mantissa >= (2 << mfmt))
    {
        mantissa >>= 1;
        exponent++;
    }
    else if(mantissa >= (1 << mfmt) && exponent == 0)
    {
        exponent++;
    }
    mantissa >>= (mfmt - wm);
    mantissa &= (1 << wm) - 1;
    if(exponent == 31)
        return (sign << 7) | 0x7B;
    return (sign << 7) | (exponent << wm) | mantissa;
}

template <int wm, int we, typename T, bool negative_zero_nan, bool clip>
MIOPEN_HIP_HOST_DEVICE uint8_t cast_to_f8(T _x, bool stoch, uint32_t rng)
{
    constexpr bool is_half  = __is_same_as(T, half);
    constexpr bool is_float = __is_same_as(T, float);
    static_assert(wm + we == 7, "wm+we==7");
    static_assert(is_half || is_float, "Only half and float can be cast to f8");

    if(sizeof(T) == 2 && we == 5 && !negative_zero_nan)
        return cast_to_f8_no_range_reduce<2, 5, half>(static_cast<half>(_x), stoch, rng);

    const int mfmt = (sizeof(T) == 4) ? 23 : 10;
    uint32_t x;
    if(sizeof(T) == 4)
        x = miopen_bit_cast<uint32_t>(_x);
    else
        x = miopen_bit_cast<uint16_t>(_x);

    uint32_t head, mantissa;
    int exponent, bias;
    uint32_t sign;

    if(sizeof(T) == 4)
    {
        head     = x & 0xFF800000;
        mantissa = x & 0x7FFFFF;
        exponent = (head >> 23) & 0xFF;
        sign     = head >> 31;
        bias     = 127;
    }
    else
    {
        head     = x & 0xFC00;
        mantissa = x & 0x3FF;
        exponent = (head >> 10) & 0x1F;
        sign     = head >> 15;
        bias     = 15;
    }

    uint32_t signed_inf = (sign << 7) + (((1 << we) - 1) << wm);

    if(negative_zero_nan)
    {
        if(sizeof(T) == 4)
        {
            if((x & 0x7F800000) == 0x7F800000)
                return 0x80;
        }
        else
        {
            // if(__hisinf(x) || __hisnan(x))
            if((x & 0x7C00) == 0x7C00)
                return 0x80;
        }
    }
    else
    {
        if(sizeof(T) == 4)
        {
            if((x & 0x7F800000) == 0x7F800000)
                return signed_inf + (mantissa != 0 ? 1 : 0);
        }
        else
        {
            if((x & 0x7C00) == 0x7C00)
                return signed_inf + (mantissa != 0 ? 1 : 0);
        }
    }
    if(x == 0)
        return 0;
    // First need to check if it is normal or denorm as there is a difference of implict 1
    // Then need to adjust the exponent to align with the F8 exponent, in the meanwhile, shift
    // The mantissa. Then for stochastic rounding, add rng to mantissa and truncate. And for
    // RNE, no need to add rng. Then probably need to check whether there is carry and adjust
    // exponent and mantissa again

    // For IEEE bias mode, the bias is 2^(k-1) -1 where k is the width of exponent bits
    const int f8_bias                  = (1 << (we - 1)) - 1 + (negative_zero_nan ? 1 : 0);
    const int f8_denormal_act_exponent = 1 - f8_bias; // actual exponent of f8 denormal
    // act_exponent is the actual exponent of fp32/fp16 (after subtracting bias)
    // f8_exponent is the converted f8 exponent with bias encoding
    // exponent_diff is the diff between fp32/fp16 exponent and f8 exponent,
    // the difference needs to be adjusted and mantissa shifted
    int act_exponent, f8_exponent, exponent_diff;

    if(exponent == 0)
    { // fp32/fp16 is in denormal.
        /* fp32 denormal is below 2^-127 so it is usually not a concern here, we mostly concern fp16
           here. In this case, f8 is usually in denormal. But there could be exceptions. fp16
           denormal has exponent bias 15 while bf8 with NANOO has exponent bias 16. It means that
           there are some numbers in fp16 denormal but they are bf8 (NANOO) normals - smallest bf8
           (NANOO) normal is 2^-15. fp16 numbers where exponent==0 (actual exponent -14) and highest
           bit of mantissa is 1 are bf8 (NANOO) normal. In this case, the fp16 mantissa should be
           shift left by 1  */
        act_exponent  = exponent - bias + 1;
        exponent_diff = f8_denormal_act_exponent -
                        act_exponent; // actual exponent is exponent-bias+1 as it is denormal
    }
    else
    { // fp32/fp16 is normal with implicit 1
        act_exponent = exponent - bias;
        if(act_exponent <= f8_denormal_act_exponent)
        {
            /* This is the case where fp32/fp16 is normal but it is in f8 denormal range.
               For example fp8 nanoo mode, denormal exponent is -7, but if the fp32/fp16
               actual exponent is -7, it is actually larger due to the implict 1,
               Therefore it needs to be adjust to -6 and mantissa shift right by 1.
               So for fp32/fp16, exponent -8 is the cut point to convert to fp8 nanoo */
            exponent_diff = f8_denormal_act_exponent - act_exponent;
        }
        else
        { // both fp32/fp16 and f8 are in normal range
            exponent_diff =
                0; // exponent_diff=0 does not mean there is no difference for this case,
                   // act_exponent could be larger. Just that it does not need shift mantissa
        }
        mantissa += (1 << mfmt); // Add the implicit 1 into mantissa
    }

    bool midpoint;
    if(exponent_diff <= wm)
        midpoint = (mantissa & ((1 << (mfmt - wm + exponent_diff)) - 1)) ==
                   (1 << (mfmt - wm + exponent_diff - 1));
    else
        midpoint = false;
    /* This part is a bit tricky. The judgment of whether it is a tie needs to be done before we
       shift right as shift right could rip off some residual part and make something not midpoint
       look like midpoint. For example, the fp16 number 0x1002 (0 00100 0000000010), it is larger
       than midpoint, but after shift right by 4 bits, it would look like midpoint.
       */

    if(exponent_diff > 0)
        mantissa >>= exponent_diff;
    else if(exponent_diff == -1)
        mantissa <<= -exponent_diff;
    bool implicit_one = mantissa & (1 << mfmt);
    // if there is no implict 1, it  means the f8 is denormal and need to adjust to denorm exponent
    f8_exponent =
        (act_exponent + exponent_diff) /*actual f8 exponent*/ + f8_bias - (implicit_one ? 0 : 1);

    // Now we have the exponent and mantissa adjusted
    uint32_t drop_mask = (1 << (mfmt - wm)) - 1;
    bool odd =
        mantissa & (1 << (mfmt - wm)); // if the least significant bit that is not truncated is 1
    mantissa += (stoch ? rng : (midpoint ? (odd ? mantissa : mantissa - 1) : mantissa)) & drop_mask;

    // Now we deal with overflow
    if(f8_exponent == 0)
    {
        if((1 << mfmt) & mantissa)
        {
            f8_exponent = 1; // denormal overflow to become normal, promote exponent
        }
    }
    else
    {
        if((1 << (mfmt + 1)) & mantissa)
        {
            mantissa >>= 1;
            f8_exponent++;
        }
    }

    mantissa >>= (mfmt - wm);

    // above range: quantize to maximum possible float of the same sign
    const int max_exp = (1 << we) - (negative_zero_nan ? 1 : 2);
    if(f8_exponent > max_exp)
    {
        if(clip)
        {
            mantissa    = (1 << wm) - 1;
            f8_exponent = max_exp;
        }
        else
        {
            return signed_inf;
        }
    }

    if(f8_exponent == 0 && mantissa == 0)
        return negative_zero_nan ? 0 : (sign << 7);
    mantissa &= (1 << wm) - 1;
    return (sign << 7) | (f8_exponent << wm) | mantissa;
}

template <int wm, int we, typename T, bool negative_zero_nan>
MIOPEN_HIP_HOST_DEVICE T cast_from_f8(uint8_t x)
{
    constexpr bool is_half  = __is_same_as(T, half);
    constexpr bool is_float = __is_same_as(T, float);
    static_assert(is_half || is_float, "only half and float are supported");

    constexpr int weo = is_half ? 5 : 8;
    constexpr int wmo = is_half ? 10 : (is_float ? 23 : 7);

    T fInf, fNegInf, fNaN, fNeg0;
    if(is_half)
    {
        const uint16_t ihInf    = 0x7C00;
        const uint16_t ihNegInf = 0xFC00;
        const uint16_t ihNaN    = 0x7C01;
        const uint16_t ihNeg0   = 0x8000;
        fInf                    = miopen_bit_cast<half>(ihInf);
        fNegInf                 = miopen_bit_cast<half>(ihNegInf);
        fNaN                    = miopen_bit_cast<half>(ihNaN);
        fNeg0                   = miopen_bit_cast<half>(ihNeg0);
    }
    else if(is_float)
    {
        const uint32_t ifInf    = 0x7F800000;
        const uint32_t ifNegInf = 0xFF800000;
        const uint32_t ifNaN    = 0x7F800001;
        const uint32_t ifNeg0   = 0x80000000;
        fInf                    = miopen_bit_cast<float>(ifInf);
        fNegInf                 = miopen_bit_cast<float>(ifNegInf);
        fNaN                    = miopen_bit_cast<float>(ifNaN);
        fNeg0                   = miopen_bit_cast<float>(ifNeg0);
    }

    if(x == 0)
        return static_cast<T>(0);

    uint32_t sign     = x >> 7;
    uint32_t mantissa = x & ((1 << wm) - 1);
    int exponent      = (x & 0x7F) >> wm;
    if(negative_zero_nan)
    {
        if(x == 0x80)
            return fNaN;
    }
    else
    {
        if(x == 0x80)
            return fNeg0;
        if(exponent == ((1 << we) - 1))
            return (mantissa == 0) ? (sign ? fNegInf : fInf) : fNaN;
    }
    typename std::conditional<sizeof(T) == 2, uint16_t, uint32_t>::type retval;
    if(we == 5 && is_half && !negative_zero_nan)
    {
        retval = x << 8;
        return miopen_bit_cast<T>(retval);
    }

    const int exp_low_cutoff = (1 << (weo - 1)) - (1 << (we - 1)) + 1 - (negative_zero_nan ? 1 : 0);

    // subnormal input
    if(exponent == 0)
    {
        // guaranteed mantissa!=0 since cases 0x0 and 0x80 are handled above
        int sh = 1 + __builtin_clz(mantissa) - (32 - wm);
        mantissa <<= sh;
        exponent += 1 - sh;
        mantissa &= ((1 << wm) - 1);
    }
    exponent += exp_low_cutoff - 1;
    mantissa <<= wmo - wm;

    // subnormal output (occurs when T=half, we=5, negative_zero_nan=true)
    if(exponent <= 0)
    {
        mantissa |= 1 << wmo;
        mantissa >>= 1 - exponent;
        exponent = 0;
    }

    if(sizeof(T) == 2)
        retval = (sign << 15) | (exponent << 10) | mantissa;
    else
        retval = (sign << 31) | (exponent << 23) | mantissa;
    return miopen_bit_cast<T>(retval);
}

} // namespace miopen_hip_f8_impl
