94inline void mul64x64_128(uint64_t a, uint64_t b, uint64_t* lo, uint64_t* hi)
96#if defined(BOTAN_FAST_64X64_MUL)
97 BOTAN_FAST_64X64_MUL(a, b, lo, hi);
105 const size_t HWORD_BITS = 32;
106 const uint32_t HWORD_MASK = 0xFFFFFFFF;
108 const uint32_t a_hi = (a >> HWORD_BITS);
109 const uint32_t a_lo = (a & HWORD_MASK);
110 const uint32_t b_hi = (b >> HWORD_BITS);
111 const uint32_t b_lo = (b & HWORD_MASK);
113 uint64_t x0 =
static_cast<uint64_t
>(a_hi) * b_hi;
114 uint64_t x1 =
static_cast<uint64_t
>(a_lo) * b_hi;
115 uint64_t x2 =
static_cast<uint64_t
>(a_hi) * b_lo;
116 uint64_t x3 =
static_cast<uint64_t
>(a_lo) * b_lo;
119 x2 += x3 >> HWORD_BITS;
125 x0 +=
static_cast<uint64_t
>(
static_cast<bool>(x2 < x1)) << HWORD_BITS;
127 *hi = x0 + (x2 >> HWORD_BITS);
128 *lo = ((x2 & HWORD_MASK) << HWORD_BITS) + (x3 & HWORD_MASK);