Joerg Sonnenberger wrote in <yotyoddlj4yqv...@bec.de>: |Am Wed, May 18, 2022 at 12:49:21PM +0200 schrieb Steffen Nurpmeso: |> What surprised me was that the Apple code requires more calls, and |> that today divisions and multiplications still matter. I think it |> was the Cyrix 166+ (or was it Athlon 1600+) where +,-,<<,>> was |> one cycle, * was ten cycles, and %,/ was fourty cycles. But |> i think the Core i5 8th Gen that i have requires one cycle for all |> of them. | |I dare you to find any CPU optimized for speed where division and modulo |are as fast as multiplication. What you have nowadays is a single cycle |for basic operations like additions and shifts, about three cycles for |multiplications (on x86 at least) and an order of magnitude more for |division. That's not really surprising either if you consider that
Thanks. I really had not looked since about 2005. (In fact i never really looked, i think a c't magazine CD once came over with x86 interrupt lists, CPU cycle usage, and a (sketchy) RFC collection.) Hm, it even seems the number of cycles increased for division .. i do not know which numbers i had seen by then, did they include cache work at all? Well. So this was that. |integer multiplication has a fast circuit implementation where as |division is often implemented as cascading conditional subtraction. |The difference matters enough turning the reminder operation in the ELF |hash into essentially (x - x * (1/size) * size) give a 2% speed up for a |large application like Firefox ten years ago. Interesting. Well you live in pkgsrc with all the mess that all those huge software suites introduce, whereas i still "jerk" if i produce software which needs more than EXEC (/ RODATA) and BSS, and "shudder" for all the CTOR and DTOR and TLS (but ok: cool) and all the other stuff that is found in ELF, and handled by the linker. (I have ELF v1.2 and TLS-ABI, and even glanced over them a really long time ago though. But you know, it is so far off! And it makes no fun thinking about that :)) |Joerg --End of <yotyoddlj4yqv...@bec.de> --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)
