Eli Zaretskii wrote:
> Well, the FP calculations in Lisp are certainly in places that get
> used a lot: the line-move stuff and window.el stuff.

OK, I constructed a little benchmark based on some of the window.el stuff, and 
timed it with immediate floats instead of the longstanding way of implementing 
floats as pointers into the heap, and on this benchmark Emacs was 82% faster 
with immediate floats, i.e., the CPU time on my usual 64-bit platform for (bench 
1000000) shrank from 10.776 now to 5.914 seconds with immediate floats. So it 
looks promising. This was the only benchmark I tried.

Patch to Emacs and benchmark source code attached. The benchmark was 
byte-compiled. The Emacs patch is just a hack; it's not intended to be a real 
implementation.