问题描述
考虑以下 C++ 代码:
Consider the following C++ code:
double someZero = 0;
std::cout << 0 - someZero << '
'; // prints 0
std::cout << -someZero << std::endl; // prints -0
问题出现了:负零有什么好处，是否应该防御性地避免它(即使用减法而不是在变量上加上减号)?
The question arises: what is negative zero good for, and should it be defensively avoided (i.e. use subtraction instead of smacking a minus onto a variable)?
推荐答案
来自维基百科:
据称，IEEE 754 中包含有符号零使得在一些关键问题[1] 中实现数值精度变得更加容易，特别是在使用复杂基本函数进行计算时[2].
It is claimed that the inclusion of signed zero in IEEE 754 makes it much easier to achieve numerical accuracy in some critical problems[1], in particular when computing with complex elementary functions[2].
第一个参考文献是 W. Kahan 的Branch Cuts for Complex Elementary Functions or Much Ado About Nothing's Sign Bit"，可供下载这里.
The first reference is "Branch Cuts for Complex Elementary Functions or Much Ado About Nothing's Sign Bit" by W. Kahan, that is available for download here.
该论文中的一个例子是 1/(+0) vs 1/(-0).在这里，零的符号有很大的不同，因为第一个表达式等于 +inf 而第二个表达式等于 -inf.
One example from that paper is 1/(+0) vs 1/(-0). Here, the sign of zero makes a huge difference, since the first expression equals +inf and the second, -inf.
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