And it's probable that the developer is comparing code compiled at -O0 (no optimization) against hand-coded assembler, like they did the last time they claimed

And it's probable that the developer is comparing code compiled at -O0 (no optimization) against hand-coded assembler, like they did the last time they claimed a 90x speed up. So just to to summary: either a 100x, or a 100% speedup (depending on which source) - comparing hand-coded assembler vs. unoptimized C code. - on a function that was poorly written in the first place. - in code that's so rarely used that nobody could be bothered to fix it for decades. - and even then, a tiny function whose overall CPU cost was about 2% of CPU cost to perform the obsolete task that nobody cared about enough to fix. - so basically code that fails the profile before optimize rule, and should never have been optimized in the first place. I think that covers it.