Great idea! Thanks. I'd tried gcc -S. Whew is my ASM rusty. But objdump -d doesn't show any rsqrt instructions.
On 1/7/21 3:46 PM, Marcus Daniels wrote: > There's a reciprocal sqrt instruction in SSE (x86) that your compiler may be > pattern matching to, depending on your compiler options. You could > disassemble to see what you get from the latter. > > -----Original Message----- > From: Friam <[email protected]> On Behalf Of u?l? ??? > Sent: Thursday, January 7, 2021 3:24 PM > To: FriAM <[email protected]> > Subject: [FRIAM] Q_rsqrt() vs 1/sqrt() > > https://en.wikipedia.org/wiki/Fast_inverse_square_root > > So, why is Q_rsqrt() *slower* than 1/sqrt()? > > 1/sqrt() took 0.294771 s > Q_rsqrt() took 0.51579 s > -- ↙↙↙ uǝlƃ - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . FRIAM Applied Complexity Group listserv Zoom Fridays 9:30a-12p Mtn GMT-6 bit.ly/virtualfriam un/subscribe http://redfish.com/mailman/listinfo/friam_redfish.com archives: http://friam.471366.n2.nabble.com/ FRIAM-COMIC http://friam-comic.blogspot.com/
