double exclamation mark meaning ?
Hi, # define likely(x) __builtin_expect(!!(x), 1) # define unlikely(x) __builtin_expect(!!(x), 0) I see these !! in the above expressions. Please explain me the meaning of those double exclamations. What is their significance ? -- Shraddha
Hi,
# define likely(x) __builtin_expect(!!(x), 1) # define unlikely(x) __builtin_expect(!!(x), 0)
I see these !! in the above expressions. Please explain me the meaning of those double exclamations. What is their significance ?
This is a kind of cast to a "bool". After applying !!(x), the value will be either 0 or 1. It's roughly equivalent to (((x) != 0) ? 1 : 0) Regards. -- Yann Droneaud OPTEYA
Hi, On Thu, Dec 6, 2012 at 3:20 PM, Shraddha Kamat <sh2008ka@gmail.com> wrote:
Hi,
# define likely(x) __builtin_expect(!!(x), 1) # define unlikely(x) __builtin_expect(!!(x), 0)
I see these !! in the above expressions. Please explain me the meaning of those double exclamations. What is their significance ?
The Operator ! is used to perform the Boolean operation NOT. For example: !(1) ---> Outputs to 0 (false). !(2.56565) ---> Outputs to 0 (false). !(2000000000) --------> Outputs to 0 (false). !(-123)---> Outputs to 0 (false). !(0)---------> Outputs to 1 (true). Similarly '!!' Performs twice NOT operation !!(1) ---> Outputs to 1 (true). !!(2.56565) ---> Outputs to 1 (true). !!(2000000000) --------> Outputs to 1 (true). !!(-123)---> Outputs to 1 (true). !!(0)---------> Outputs to 0 (false). Hope that clears your doubt. Regards, --Prabhakar Lad
-- Shraddha
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On Thu, Dec 6, 2012 at 4:50 AM, Shraddha Kamat <sh2008ka@gmail.com> wrote:
Hi,
# define likely(x) __builtin_expect(!!(x), 1) # define unlikely(x) __builtin_expect(!!(x), 0)
I see these !! in the above expressions. Please explain me the meaning of those double exclamations. What is their significance ?
this is c question, right, google is your friend
-- Shraddha
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participants (4)
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devendra.aaru -
Prabhakar Lad -
Shraddha Kamat -
Yann Droneaud