【C/C++】将32位int转化为double_c语言 uint32强转成double有问题吗-优快云博客

本文链接：https://blog.youkuaiyun.com/cwb0525/article/details/6862542

本文介绍了如何在C/C++中将32位整型数值转换为double类型，通过深入解析V8引擎源码中的实现方式，揭示底层转换原理。

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闲来无事，看看了V8的代码，在V8.cc中有这么一段：

// Use a union type to avoid type-aliasing optimizations in GCC.
typedef union {
  double double_value;
  uint64_t uint64_t_value;
} double_int_union;


Object* V8::FillHeapNumberWithRandom(Object* heap_number, Isolate* isolate) {
  uint64_t random_bits = Random(isolate);
  // Make a double* from address (heap_number + sizeof(double)).
  double_int_union* r = reinterpret_cast<double_int_union*>(
      reinterpret_cast<char*>(heap_number) +
      HeapNumber::kValueOffset - kHeapObjectTag);
  // Convert 32 random bits to 0.(32 random bits) in a double
  // by computing:
  // ( 1.(20 0s)(32 random bits) x 2^20 ) - (1.0 x 2^20)).
  const double binary_million = 1048576.0;
  r->double_value = binary_million;
  r->uint64_t_value |=  random_bits;
  r->double_value -= binary_million;

  return heap_number;
}