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27
28
29#include "diy-fp.h"
30#include "utils.h"
31
32namespace double_conversion {
33
34void DiyFp::Multiply(const DiyFp& other) {
35 // Simply "emulates" a 128 bit multiplication.
36 // However: the resulting number only contains 64 bits. The least
37 // significant 64 bits are only used for rounding the most significant 64
38 // bits.
39 const uint64_t kM32 = 0xFFFFFFFFU;
40 uint64_t a = f_ >> 32;
41 uint64_t b = f_ & kM32;
42 uint64_t c = other.f_ >> 32;
43 uint64_t d = other.f_ & kM32;
44 uint64_t ac = a * c;
45 uint64_t bc = b * c;
46 uint64_t ad = a * d;
47 uint64_t bd = b * d;
48 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32);
49 // By adding 1U << 31 to tmp we round the final result.
50 // Halfway cases will be round up.
51 tmp += 1U << 31;
52 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
53 e_ += other.e_ + 64;
54 f_ = result_f;
55}
56
57} // namespace double_conversion
58