/*

* A minimal 128-bit integer type for curve25519-donna

* (C) 2014 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#ifndef BOTAN_CURVE25519_DONNA128_H_

#define BOTAN_CURVE25519_DONNA128_H_

#include <botan/internal/mul128.h>

#include <type_traits>

namespace Botan {

class donna128 final {

   public:

      constexpr donna128(uint64_t ll = 0, uint64_t hh = 0) {

         l = ll;

         h = hh;

      }

      donna128(const donna128&) = default;

      donna128& operator=(const donna128&) = default;

      template <typename T>

      constexpr friend donna128 operator>>(const donna128& x, T shift) {

         donna128 z = x;

         if(shift > 64) {

            z.l = z.h >> (shift - 64);

            z.h = 0;

         } else if(shift == 64) {

            z.l = z.h;

            z.h = 0;

         } else if(shift > 0) {

            const uint64_t carry = z.h << static_cast<size_t>(64 - shift);

            z.h >>= shift;

            z.l >>= shift;

            z.l |= carry;

         }

         return z;

      }

      template <typename T>

      constexpr friend donna128 operator<<(const donna128& x, T shift) {

         donna128 z = x;

         if(shift > 64) {

            z.h = z.l << (shift - 64);

            z.l = 0;

         } else if(shift == 64) {

            z.h = z.l;

            z.l = 0;

         } else if(shift > 0) {

            const uint64_t carry = z.l >> static_cast<size_t>(64 - shift);

            z.l = (z.l << shift);

            z.h = (z.h << shift) | carry;

         }

         return z;

      }

      constexpr friend uint64_t operator&(const donna128& x, uint64_t mask) { return x.l & mask; }

      constexpr uint64_t operator&=(uint64_t mask) {

         h = 0;

         l &= mask;

         return l;

      }

      constexpr donna128& operator+=(const donna128& x) {

         l += x.l;

         h += x.h;

         const uint64_t carry = (l < x.l);

         h += carry;

         return *this;

      }

      constexpr donna128& operator+=(uint64_t x) {

         l += x;

         const uint64_t carry = (l < x);

         h += carry;

         return *this;

      }

      constexpr uint64_t lo() const { return l; }

      constexpr uint64_t hi() const { return h; }

      constexpr operator uint64_t() const { return l; }

   private:

      uint64_t h = 0, l = 0;

};

template <std::unsigned_integral T>

constexpr inline donna128 operator*(const donna128& x, T y) {

   BOTAN_ARG_CHECK(x.hi() == 0, "High 64 bits of donna128 set to zero during multiply");

   uint64_t lo = 0, hi = 0;

   mul64x64_128(x.lo(), static_cast<uint64_t>(y), &lo, &hi);

   return donna128(lo, hi);

}

template <std::unsigned_integral T>

constexpr inline donna128 operator*(T y, const donna128& x) {

   return x * y;

}

constexpr inline donna128 operator+(const donna128& x, const donna128& y) {

   donna128 z = x;

   z += y;

   return z;

}

constexpr inline donna128 operator+(const donna128& x, uint64_t y) {

   donna128 z = x;

   z += y;

   return z;

}

constexpr inline donna128 operator|(const donna128& x, const donna128& y) {

   return donna128(x.lo() | y.lo(), x.hi() | y.hi());

}

constexpr inline donna128 operator|(const donna128& x, uint64_t y) {

   return donna128(x.lo() | y, x.hi());

}

constexpr inline uint64_t carry_shift(const donna128& a, size_t shift) {

   return (a >> shift).lo();

}

constexpr inline uint64_t combine_lower(const donna128& a, size_t s1, const donna128& b, size_t s2) {

   donna128 z = (a >> s1) | (b << s2);

   return z.lo();

}

#if defined(BOTAN_TARGET_HAS_NATIVE_UINT128)

inline uint64_t carry_shift(const uint128_t a, size_t shift) {

   return static_cast<uint64_t>(a >> shift);

}

inline uint64_t combine_lower(const uint128_t a, size_t s1, const uint128_t b, size_t s2) {

   return static_cast<uint64_t>((a >> s1) | (b << s2));

}

#endif

}  // namespace Botan

#endif