24constexpr inline void mul64x64_128(uint64_t a, uint64_t b, uint64_t* lo, uint64_t* hi) {
25 if(!std::is_constant_evaluated()) {
26#if defined(BOTAN_BUILD_COMPILER_IS_MSVC) && defined(BOTAN_TARGET_ARCH_IS_X86_64)
27 *lo = _umul128(a, b, hi);
30#elif defined(BOTAN_BUILD_COMPILER_IS_MSVC) && defined(BOTAN_TARGET_ARCH_IS_ARM64)
37#if defined(BOTAN_TARGET_HAS_NATIVE_UINT128)
38 const uint128_t r =
static_cast<uint128_t
>(a) * b;
39 *hi = (r >> 64) & 0xFFFFFFFFFFFFFFFF;
40 *lo = (r) & 0xFFFFFFFFFFFFFFFF;
47 const size_t HWORD_BITS = 32;
48 const uint32_t HWORD_MASK = 0xFFFFFFFF;
50 const uint32_t a_hi = (a >> HWORD_BITS);
51 const uint32_t a_lo = (a & HWORD_MASK);
52 const uint32_t b_hi = (b >> HWORD_BITS);
53 const uint32_t b_lo = (b & HWORD_MASK);
55 const uint64_t x0 =
static_cast<uint64_t
>(a_hi) * b_hi;
56 const uint64_t x1 =
static_cast<uint64_t
>(a_lo) * b_hi;
57 const uint64_t x2 =
static_cast<uint64_t
>(a_hi) * b_lo;
58 const uint64_t x3 =
static_cast<uint64_t
>(a_lo) * b_lo;
61 const uint64_t middle = x2 + (x3 >> HWORD_BITS) + (x1 & HWORD_MASK);
64 *hi = x0 + (middle >> HWORD_BITS) + (x1 >> HWORD_BITS);
65 *lo = (middle << HWORD_BITS) + (x3 & HWORD_MASK);