[tarantool-patches] Re: [PATCH] sql: LIKE/LENGTH process '\0'

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

On 20/02/2019 19:04, n.pettik wrote:
> 
> 
>> On 20 Feb 2019, at 18:47, i.koptelov <ivan.koptelov@tarantool.org> wrote:
>>
>> Thanks to Alexander, I fixed my patch to use a function
>> from icu to count the length of the string.
>>
>> Changes:
>>
> 
> Look, each next implementation again and again changes
> results of certain tests. Lets firstly define exact behaviour of
> length() function and then write function which will satisfy these
> requirements, not vice versa. Is this the final version?
> Moreover, since Konstantin suggest as fast implementation
> as we can, I propose to consider sort of asm written variant:
> 
>          .global ap_strlen_utf8_s
> ap_strlen_utf8_s:
>          push %esi
>          cld
>          mov 8(%esp), %esi
>          xor %ecx, %ecx
> loopa:  dec %ecx
> loopb:  lodsb
>          shl $1, %al
>          js loopa
>          jc loopb
>          jnz loopa
>          mov %ecx, %eax
>          not %eax
>          pop %esi
>          ret
> 
> 
> It is taken from http://canonical.org/~kragen/strlen-utf8
> and author claims that quite fast (seems like it doesn’t
> handle \0, but we can patch it). I didn’t bench it, so I am
> not absolutely sure that it ‘way faster’ than other implementations.

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