[Bug libc/15884] Big performance problem in strcoll

["neleai at seznam dot cz" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=15884

Ondrej Bilka <neleai at seznam dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |---
            Summary|Big performance regression  |Big performance problem in
                   |in strcoll                  |strcoll

--- Comment #3 from Ondrej Bilka <neleai at seznam dot cz> ---
I thougth that originaly a comparison was done character-by-character without
useless allocation, after looking through history I was mistaken. Changing
regression->problem.

> Also, the test case is invalid.  It compares a space with an exclamation  
> point, both of which are ignored as collation sequences due to which the 
> algorithm actually goes through all the passes for the string before it 
> compares them on a binary level.  Replace 32 and 33 with 'a' and 'b' and 
> you'll see the difference.

it is still there, just smaller multiplicative factor hidden it into loop
overhead for smaller lengths. When changed to a/b time becomes:

ondra@neklekam:~$ gcc -DN=1 strcoll.c ; time ./a.out

real    0m0.040s
user    0m0.037s
sys    0m0.000s

ondra@neklekam:~$ gcc -DN=10 strcoll.c ; time ./a.out

real    0m0.039s
user    0m0.037s
sys    0m0.003s
ondra@neklekam:~$ gcc -DN=100 strcoll.c ; time ./a.out

real    0m0.044s
user    0m0.043s
sys    0m0.007s
ondra@neklekam:~$ gcc -DN=1000 strcoll.c ; time ./a.out

real    0m0.115s
user    0m0.113s
sys    0m0.000s
ondra@neklekam:~$ gcc -DN=10000 strcoll.c ; time ./a.out

real    0m0.737s
user    0m0.737s
sys    0m0.000s
ondra@neklekam:~$ gcc -DN=100000 strcoll.c ; time ./a.out

real    0m7.443s
user    0m7.443s
sys    0m0.000s

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