third_party/WebKit/Source/wtf/dtoa/diy-fp.cc

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