"I've been writing C for quite some time, but I never followed good conventions I'm afraid, and I never payed much attention to the optimization tricks of the higher C programmers. Sure, I use const when I can, I use the pointer methods for manual string copying, I even use register for all the good that does with modern compilers, but now, I'm trying to write a C-string handling library for personal use, but I need speed, and I really don't want to use inline ASM. So, I am wondering, what would other Soylenters do to write efficient, pure, standards-compliant C?"
I've dealt with plenty of "don't worry I'm a game developer, I'm the best kind of programmer there is" programmers, your post is almost cliche. It's almost entertaining to tear their illusions down on StackOverflow, because they are so full of themselves, both when asking and answering questions. It's easy to spot them, because they always start their posts with "I'm a game programmer".
Here are some hard truths:
"The world is full of differences, learn to bare with it."
Indeed, if we all bare with it then some major differences that split the world population in two will become obvious.