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27
28#include "config.h"
29
30#include <wtf/dtoa/diy-fp.h>
31#include <wtf/dtoa/utils.h>
32
33namespace WTF {
34namespace double_conversion {
35
36void DiyFp::Multiply(const DiyFp& other) {
37 // Simply "emulates" a 128 bit multiplication.
38 // However: the resulting number only contains 64 bits. The least
39 // significant 64 bits are only used for rounding the most significant 64
40 // bits.
41 const uint64_t kM32 = 0xFFFFFFFFU;
42 uint64_t a = f_ >> 32;
43 uint64_t b = f_ & kM32;
44 uint64_t c = other.f_ >> 32;
45 uint64_t d = other.f_ & kM32;
46 uint64_t ac = a * c;
47 uint64_t bc = b * c;
48 uint64_t ad = a * d;
49 uint64_t bd = b * d;
50 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32);
51 // By adding 1U << 31 to tmp we round the final result.
52 // Halfway cases will be round up.
53 tmp += 1U << 31;
54 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32);
55 e_ += other.e_ + 64;
56 f_ = result_f;
57}
58
59} // namespace double_conversion
60} // namespace WTF
61