TDH1978 <thedeerhunter1978@movie.uni> writes:

I googled this and could not find an answer. I know that the
gcc-specific keywords "likely" and "unlikely" can be useful in 'if' conditions

if (unlikely(i < 0))
// action

but can they be used in a 'while' loop?

while (likely(i > 0))
// action

The GCC-specific keyword is __builtin_expect, documented in https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/Other-Builtins.html

‘likely’ and ‘unlikely’ are macros defined using this keyword in some projects (e.g. the Linux kernel).

--
http://www.greenend.org.uk/rjk/

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I googled this and could not find an answer. I know that the
gcc-specific keywords "likely" and "unlikely" can be useful in 'if'
conditions

if (unlikely(i < 0))
// action

but can they be used in a 'while' loop?

while (likely(i > 0))
// action

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On Fri, 2017-03-17, TDH1978 wrote:

I googled this and could not find an answer. I know that the
gcc-specific keywords "likely" and "unlikely" can be useful in 'if'

Like someone else explained, they actual keyword is different.

conditions

if (unlikely(i < 0))
// action

but can they be used in a 'while' loop?

while (likely(i > 0))
// action

I expect so. Why not? while(unlikely(...)) seems more useful than while(likely(...)) since I expect the compiler to optimize for the
latter case by default.

And there are around 150 examples in the Linux kernel (or was in
3.16.7, which I happened to have handy).

It's probably not something you should sprinkle your code with though.

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .

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