* how is strcmp implemented so efficiently?
@ 2008-09-30 22:40 Reza Roboubi
2008-09-30 22:55 ` me22
2008-10-01 0:58 ` Ian Lance Taylor
0 siblings, 2 replies; 3+ messages in thread
From: Reza Roboubi @ 2008-09-30 22:40 UTC (permalink / raw)
To: gcc-help
I noticed that strcmp is extremely smart. It knows when one parameter
has constant length, determined at compile time. In that case it
reverts to an inline version of the x86 string commands.
I looked into the headers and strcmp is defined as an extern(not inline.)
How would I ever write such an efficient function? Is it possible(even
_with_ the use of asm?!)
Reza.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: how is strcmp implemented so efficiently?
2008-09-30 22:40 how is strcmp implemented so efficiently? Reza Roboubi
@ 2008-09-30 22:55 ` me22
2008-10-01 0:58 ` Ian Lance Taylor
1 sibling, 0 replies; 3+ messages in thread
From: me22 @ 2008-09-30 22:55 UTC (permalink / raw)
To: Reza Roboubi; +Cc: gcc-help
On Tue, Sep 30, 2008 at 18:40, Reza Roboubi <reza@parvan.net> wrote:
> I noticed that strcmp is extremely smart. It knows when one parameter has
> constant length, determined at compile time. In that case it reverts to an
> inline version of the x86 string commands.
>
Sounds like one of the optimizer passes has special-case code to handle it.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: how is strcmp implemented so efficiently?
2008-09-30 22:40 how is strcmp implemented so efficiently? Reza Roboubi
2008-09-30 22:55 ` me22
@ 2008-10-01 0:58 ` Ian Lance Taylor
1 sibling, 0 replies; 3+ messages in thread
From: Ian Lance Taylor @ 2008-10-01 0:58 UTC (permalink / raw)
To: Reza Roboubi; +Cc: gcc-help
Reza Roboubi <reza@parvan.net> writes:
> I noticed that strcmp is extremely smart. It knows when one parameter
> has constant length, determined at compile time. In that case it
> reverts to an inline version of the x86 string commands.
>
> I looked into the headers and strcmp is defined as an extern(not inline.)
>
> How would I ever write such an efficient function? Is it
> possible(even _with_ the use of asm?!)
The compiler automatically recognizes strcmp when compiling C/C++
code, among many other builtin functions. See the docs for the
complete list.
Ian
^ permalink raw reply [flat|nested] 3+ messages in thread
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2008-09-30 22:40 how is strcmp implemented so efficiently? Reza Roboubi
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