交换两个int值的最短代码

CSDN上的帖子http://community.csdn.net/Expert/TopicView3.asp?id=4899577

比较好的是它着重考虑了“极端情况”----防止溢出

总结起来有如下几个
a^=b^=a^=b;
b=a+(a=b)*0;
a=b|a&~(b=a);
这三个在C#下应该都行，但是在C++下只有第一个行

原因是C#和C++对表达式求值顺序上不同，
如a=f(i)+g(i++)+h(i);中f，g用的都是i旧值，h则用的新值，C++则是未应义。
又如c=a+(a=1);C#中c应该是a旧值加1,C++则是2
C#中一个表达式中一个变量取值是按照从左至右的,C++则是按运算优先级的。

我觉得还是C#的顺序比较好，不过用C++多了总觉得它怪怪的。
另外C++未定义的那个太不好了，据说是因为编译器先于标准出现

Comments

Determine Perspective Lines With Off-page Vanishing Point

In perspective drawing, a vanishing point represents a group of parallel lines, in other words, a direction. For any point on the paper, if we want a line towards the same direction (in the 3d space), we simply draw a line through it and the vanishing point. But sometimes the vanishing point is too far away, such that it is outside the paper/canvas. In this example, we have a point P and two perspective lines L1 and L2. The vanishing point VP is naturally the intersection of L1 and L2. The task is to draw a line through P and VP, without having VP on the paper. I am aware of a few traditional solutions: 1. Use extra pieces of paper such that we can extend L1 and L2 until we see VP. 2. Draw everything in a smaller scale, such that we can see both P and VP on the paper. Draw the line and scale everything back. 3. Draw a perspective grid using the Brewer Method. #1 and #2 might be quite practical. #3 may not guarantee a solution, unless we can measure distances/p...

Chasing an IO Phantom

My home server has been weird since months ago, it just becomes unresponsive occassionally. It is annoying but it happens only rarely, so normally I'd just wait or reboot it. But weeks ago I decided to get to the bottom of it. What's Wrong My system set up is: Root: SSD, LUKS + LVM + Ext4 Data: HDD, LUKS + ZFS 16GB RAM + 1GB swap Rootless dockerd The system may become unresponsive, when the IO on HDD is persistantly high for a while. Also: Often kswapd0 has high CPU High IO on root fs (SSD) From dockerd and some containers RAM usage is high, swap usage is low It is very strange that IO on HDD can affect SSD. Note that when this happens, even stopping the IO on HDD does not always help. Usually restarting dockerd does not help, but rebooting helps. Investigation: Swap An obvious potential root cause is the swap. High CPU on kswapd0 usually means the free memory is low and the kernel is busy exchanging data between disk and swap. However, I tried the following steps, none of the...

Moving Items Along Bezier Curves with CSS Animation (Part 2: Time Warp)

This is a follow-up of my earlier article. I realized that there is another way of achieving the same effect. This article has lots of nice examples and explanations, the basic idea is to make very simple @keyframe rules, usually just a linear movement, then use timing function to distort the time, such that the motion path becomes the desired curve. I'd like to call it the "time warp" hack. Demo See the Pen Interactive cubic Bezier curve + CSS animation by Lu Wang ( @coolwanglu ) on CodePen . How does it work? Recall that a cubic Bezier curve is defined by this formula : \[B(t) = (1-t)^3P_0+3(1-t)^2tP_1+3(1-t)t^2P_2+t^3P_3,\ 0 \le t \le 1.\] In the 2D case, \(B(t)\) has two coordinates, \(x(t)\) and \(y(t)\). Define \(x_i\) to the be x coordinate of \(P_i\), then we have: \[x(t) = (1-t)^3x_0+3(1-t)^2tx_1+3(1-t)t^2x_2+t^3x_3,\ 0 \le t \le 1.\] So, for our animated element, we want to make sure that the x coordiante (i.e. the "left" CSS property) is \(...

WangLu's Notes

Search This Blog