如何在C中尽可能快地标记数组中的数据重复？

I have made half a program that does some major floating point math. Depending on the data it started with, it can generate very large arrays that describe line segments. The positions of these line segments are recorded using the Cartesian coordinate system with floating point numbers to record the X,Y,Z positions of each end of the line. I cant use X,Y,Z for both ends so I used X,Y,Z for the start, and Q,R,S for the end. So basically what I want to do, is flag all lines that are identical or flipped so that Q,R,S one line one is equal to X,Y,Z on line two and X,Y,Z on line one is equal to Q,R,S on line two. My current flagging technique is to set X to -1 because I know that none of the lines will ever end up with negative coordinates. I don't want to flag both lines, just all of them except for one. This is my current function:I have made half a program that does some major