Hi, Double logical negation is the simplest way of doing: if(x) x=1; which is limiting the value of x to either 0 or 1. HTH Thanks & regards, Suvidh Mathur -----Original Message----- From: Borislav Petkov [mailto:petkov@uni-muenster.de] Sent: Thursday, July 01, 2004 1:20 PM To: kernelnewbies@nl.linux.org Subject: solved: {un}likely macros? -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Thursday 01 July 2004 09:35, Borislav Petkov wrote: > Hi there people, > first of all i would like to thank everybody for their help in figuring out > the yesterday's asm oneliner. I have another q, though :) > The kernel extensively uses these macros. <snip> Forget it, i found it in the gcc manual. It uses a builtin function in gcc to do better branch prediction, so when we do likely(x), we actually do __builtin_expect(!!(x),1) which means that it is likely that x is true, i.e., x == 1 and the code after it is (more :)) likely to get executed so that the branch prediction algorithm in the processor runs faster. However, what's with the double negation of x - !!(x)? Regards, Boris. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (GNU/Linux) iD8DBQFA48IhiBySr3Fn37QRAupkAJ9M4k9+aHvoFd1l/dI0G8WjuWwCZwCdHPca B6CBl89LoMsmc5C3w1P2LPI= =gOCR -----END PGP SIGNATURE----- -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
