I think you're trying to explain what's special about the number -1227133513 or how it comes about / how one could arrive at it. This is something the author un

I think you're trying to explain what's special about the number -1227133513 or how it comes about / how one could arrive at it. This is something the author understands very well; in fact that's what the whole post is about (well, it's about more advanced matters, using this as a "hook"), and many nice methods to arrive at that number are discussed in the post and comments. (And BTW your computation corresponds to 1227133513 or -1/7, not to -1227133513 or 1/7.) The sentence you quoted is merely asking which of the many discussed methods gcc is actually using, and this cannot be answered by mathematics; it needs to be answered by pointing to the relevant source code.