vmsplice(): the making of a local root exploit

As a matter of diligence I (like many, many people) document large swathes of my code in the
form of comments. Basically anywhere it has taken me more than a moment to think about, or
where the purpose of the code cannot be inferred by reading API documentation for the calls
made inside it.

Magical integer literals and bitshifts fall well within this purview, and I cannot see it as
"noobness" in these two specific cases. Imagine someone had to go back and fix all those
bitshifts when we move to Some New Compiler (in Some Hypothetical Future). Can't be regexed,
no central place where a change can ripple through the tree, and utterly dangerous, say, if
this New Compiler takes advantage of the fact that bitwise right shift on a signed number is
undefined according to ANSI C (I'm taking this as one, single example. There are hundreds
more).

I understand that other peoples' code is difficult to comprehend. Hell, I've read more than my
fair worth of Other Peoples' Code. I'm talking specifically about why the Linux kernel seems
to be so full of this, but other commenters have given good reasons for some of this already.