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namespace double_conversion { | |
void DiyFp::Multiply(const DiyFp& other) { | |
// Simply "emulates" a 128 bit multiplication. | |
// However: the resulting number only contains 64 bits. The least | |
// significant 64 bits are only used for rounding the most significant 64 | |
// bits. | |
const uint64_t kM32 = 0xFFFFFFFFU; | |
uint64_t a = f_ >> 32; | |
uint64_t b = f_ & kM32; | |
uint64_t c = other.f_ >> 32; | |
uint64_t d = other.f_ & kM32; | |
uint64_t ac = a * c; | |
uint64_t bc = b * c; | |
uint64_t ad = a * d; | |
uint64_t bd = b * d; | |
uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); | |
// By adding 1U << 31 to tmp we round the final result. | |
// Halfway cases will be round up. | |
tmp += 1U << 31; | |
uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); | |
e_ += other.e_ + 64; | |
f_ = result_f; | |
} | |
} // namespace double_conversion | |