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 // SPDX-License-Identifier: MIT
 // Copyright (c) 2018-2023, Advanced Micro Devices, Inc. All rights reserved.
  
 #pragma once
  
 #include "ck_tile/core/config.hpp"
 #include "ck_tile/core/container/tuple.hpp"
 #include "ck_tile/core/numeric/integral_constant.hpp"
 #include "ck_tile/core/utility/bit_cast.hpp"
 #include "ck_tile/core/utility/type_traits.hpp"
 #include <stdint.h>
  
 namespace ck_tile {
  
 // magic number division
 // Caution:
 //   1. For uint32_t as dividend: magic number division implementation being used would produce
 //   correct result if the dividend is uint32_t and its value is within 31-bit value range.
 //   2. For int32_t as dividendd: magic number division for int32_t dividened has not been
 //   implemented, the int32_t dividend would be bit-wise interpreted as uint32_t and magic number
 //   division implementation for uint32_t is then used. Therefore, dividend value need to be
 //   non-negative.
 // TODO:
 //   1. Implement magic number divison for int32_t
 //   2. Implement magic number divison for unit32_t with 32-bit value range
 struct magic_division32_bit_range
 {
     // uint32_t
     CK_TILE_HOST_DEVICE static constexpr auto calculate_magic_numbers(uint32_t divisor)
     {
         // WARNING: magic division is only valid for division inside this range.
         // assert(divisor >= 1 && divisor <= INT32_MAX)
  
         uint32_t shift_u32 = 0;
  
         while((1U << shift_u32) < divisor)
         {
             shift_u32++;
         };
  
         uint64_t tmp_u64        = static_cast<uint64_t>((1UL << shift_u32) - divisor) << 32;
         uint32_t multiplier_u32 = tmp_u64 / divisor + 1;
  
         return make_tuple(multiplier_u32, shift_u32);
     }
  
     template <auto Divisor, typename = std::enable_if_t<(0 < Divisor)>>
     CK_TILE_HOST_DEVICE static constexpr auto calculate_magic_numbers(constant<Divisor>)
     {
         constexpr auto tmp = calculate_magic_numbers(uint32_t{Divisor});
  
         constexpr uint32_t multiplier = tmp[number<0>{}];
         constexpr uint32_t shift      = tmp[number<1>{}];
  
         return make_tuple(constant<multiplier>{}, constant<shift>{});
     }
  
     // magic division for uint32_t
     CK_TILE_DEVICE static constexpr uint32_t
     do_magic_division(uint32_t dividend, uint32_t multiplier, uint32_t shift)
     {
         if(__builtin_is_constant_evaluated())
         {
             uint32_t tmp = (static_cast<uint64_t>(dividend) * multiplier) >> 32;
             return (tmp + dividend) >> shift;
         }
         else
         {
             uint32_t tmp = __umulhi(dividend, multiplier);
             return (tmp + dividend) >> shift;
         }
     }
  
     CK_TILE_HOST static constexpr uint32_t
     do_magic_division(uint32_t dividend, uint32_t multiplier, uint32_t shift)
     {
         uint32_t tmp = (static_cast<uint64_t>(dividend) * multiplier) >> 32;
         return (tmp + dividend) >> shift;
     }
  
     // magic division for int32_t
     // HACK: use dividend_i32 as if it's uint32_t, dividend_i32 need to be
     // non-negative for result to be correct
     // TODO: figure out how to do magic number divison for int32_t as dividended
     CK_TILE_DEVICE static constexpr int32_t
     do_magic_division(int32_t dividend_i32, uint32_t multiplier, uint32_t shift)
     {
         if(__builtin_is_constant_evaluated())
         {
             uint32_t dividend_u32 = bit_cast<uint32_t>(dividend_i32);
             uint32_t tmp          = (static_cast<uint64_t>(dividend_u32) * multiplier) >> 32;
             return (tmp + dividend_u32) >> shift;
         }
         else
         {
             uint32_t dividend_u32 = bit_cast<uint32_t>(dividend_i32);
             uint32_t tmp          = __umulhi(dividend_u32, multiplier);
             return (tmp + dividend_u32) >> shift;
         }
     }
  
     CK_TILE_HOST static constexpr int32_t
     do_magic_division(int32_t dividend_i32, uint32_t multiplier, uint32_t shift)
     {
         uint32_t dividend_u32 = bit_cast<uint32_t>(dividend_i32);
         uint32_t tmp          = (static_cast<uint64_t>(dividend_u32) * multiplier) >> 32;
         return (tmp + dividend_u32) >> shift;
     }
 };
  
 // magic number division
 // This version on works for divisor and dividended between [0, 1 << 16]
 struct magic_division16_bit_range
 {
     // uint32_t
     CK_TILE_HOST_DEVICE static constexpr auto calculate_magic_numbers(uint32_t divisor)
     {
         // WARNING: magic division is only valid for division inside this range.
         // assert(divisor >= 1 && divisor <= (1U << 16));
  
         uint32_t shift_u32 = 0;
  
         while((1U << shift_u32) < divisor)
         {
             shift_u32++;
         };
  
         uint32_t one            = 1;
         uint32_t multiplier_u32 = ((one << 16) * ((one << shift_u32) - divisor)) / divisor + 1;
  
         return make_tuple(multiplier_u32, shift_u32);
     }
  
     // integral_constant<uint32_t, .>
     template <auto Divisor>
     CK_TILE_HOST_DEVICE static constexpr auto calculate_magic_numbers(constant<Divisor>)
     {
         constexpr auto tmp = calculate_magic_numbers(uint32_t{Divisor});
  
         constexpr uint32_t multiplier = tmp[number<0>{}];
         constexpr uint32_t shift      = tmp[number<1>{}];
  
         return make_tuple(constant<multiplier>{}, constant<shift>{});
     }
  
     // magic division for uint32_t
     CK_TILE_DEVICE static constexpr uint32_t
     do_magic_division(uint32_t dividend, uint32_t multiplier, uint32_t shift)
     {
         uint32_t tmp = (dividend * multiplier) >> 16;
         return (tmp + dividend) >> shift;
     }
  
     CK_TILE_HOST static constexpr uint32_t
     do_magic_division(uint32_t dividend, uint32_t multiplier, uint32_t shift)
     {
         uint32_t tmp = (dividend * multiplier) >> 16;
         return (tmp + dividend) >> shift;
     }
  
     // magic division for int32_t
     // HACK: use dividend_i32 as if it's uint32_t, dividend_i32 need to be
     // non-negative for result to be correct
     // TODO: figure out how to do magic number divison for int32_t as dividended
     CK_TILE_DEVICE static constexpr int32_t
     do_magic_division(int32_t dividend_i32, uint32_t multiplier, uint32_t shift)
     {
         uint32_t dividend_u32 = bit_cast<uint32_t>(dividend_i32);
         uint32_t tmp          = (dividend_u32 * multiplier) >> 16;
         return (tmp + dividend_u32) >> shift;
     }
  
     CK_TILE_HOST static constexpr int32_t
     do_magic_division(int32_t dividend_i32, uint32_t multiplier, uint32_t shift)
     {
         uint32_t dividend_u32 = bit_cast<uint32_t>(dividend_i32);
         uint32_t tmp          = (dividend_u32 * multiplier) >> 16;
         return (tmp + dividend_u32) >> shift;
     }
 };
  
 // use 32bit version
 using magic_division = magic_division32_bit_range;
  
 struct mdiv
 {
     // 1 dword -> 3 dword storage
     uint32_t divisor;
     uint32_t multiplier;
     uint32_t shift; // TODO: 8 bit is enough
  
     // prefer construct on host
     CK_TILE_HOST_DEVICE mdiv(uint32_t divisor_) : divisor(divisor_)
     {
         auto tmp = magic_division::calculate_magic_numbers(divisor_);
  
         multiplier = tmp[number<0>{}];
         shift      = tmp[number<1>{}];
     }
  
     CK_TILE_HOST_DEVICE mdiv() : divisor(0), multiplier(0), shift(0) {}
  
     CK_TILE_HOST_DEVICE void update(uint32_t divisor_)
     {
         divisor  = divisor_;
         auto tmp = magic_division::calculate_magic_numbers(divisor_);
  
         multiplier = tmp[number<0>{}];
         shift      = tmp[number<1>{}];
     }
  
     CK_TILE_HOST_DEVICE uint32_t div(uint32_t dividend_) const
     {
         return magic_division::do_magic_division(dividend_, multiplier, shift);
     }
  
     CK_TILE_HOST_DEVICE void
     divmod(uint32_t dividend_, uint32_t& quotient_, uint32_t& remainder_) const
     {
         quotient_  = div(dividend_);
         remainder_ = dividend_ - (quotient_ * divisor);
     }
  
     CK_TILE_HOST_DEVICE uint32_t get() const { return divisor; }
 };
  
 struct mdiv2
 {
     // 1 dword -> 2 dword storage, divisor need compute from runtime
     uint32_t multiplier;
     uint32_t shift; // TODO: 8 bit is enough
  
     // prefer construct on host
     CK_TILE_HOST_DEVICE mdiv2(uint32_t divisor_)
     {
         auto tmp = magic_division::calculate_magic_numbers(divisor_);
  
         multiplier = tmp[number<0>{}];
         shift      = tmp[number<1>{}];
     }
  
     CK_TILE_HOST_DEVICE mdiv2() : multiplier(0), shift(0) {}
  
     CK_TILE_HOST_DEVICE uint32_t div(uint32_t dividend_) const
     {
         return magic_division::do_magic_division(dividend_, multiplier, shift);
     }
  
     CK_TILE_HOST_DEVICE void
     divmod(uint32_t dividend_, uint32_t divisor_, uint32_t& quotient_, uint32_t& remainder_) const
     {
         quotient_  = div(dividend_);
         remainder_ = dividend_ - (quotient_ * divisor_);
     }
 };
  
 } // namespace ck_tile