[fpc-devel] Performance of string handling in trunk

[Sven Barth]

Am 26.06.2013 13:59, schrieb Michael Schnell:
> BTW.
>
> I think the implementation would be quite easy, straight forward, fast 
> and compatible.
>
>  - The compiler knows the static encoding type of each string variable.
>  - The dynamic encoding type of a String is preset to the static 
> encoding type when the string is allocated
>  - only RawByteStrings (EncodingType $FFFF) are allowed to change 
> their dynamic encoding type, with other Strings this will lead to 
> unpredictable results
>
>
> When Strings are assigned:
>  - If the static encoding type of source and target is identical (be 
> it normal or RAW) (already checked by the compiler) -> the same 
> happens as with the pre-Unicode compiler (setting the pointer to the 
> StringRecord and managing the RefCount)
> otherwise:
>  - If the target is statically defined as RawByteString (already 
> checked by the compiler) -> the same happens
>  - If the source is statically defined as RawByteString (already 
> checked by the compiler), code is implemented that checks if the 
> dynamic encoding of the source is identical to the (known to the 
> compiler) static encoding type of the target -> the same happens
>
> otherwise the conversion library is called. Same checks the _dynamic_ 
> encoding type of source and target (thus it only needs to be provided 
> with the Strings themselves and no additional information generated by 
> the compiler) and does the conversion appropriately.
>
>
> When doing operation on two Strings (such as "+" and compare), one of 
> the operators is (virtually) copied to a String with the same encoding 
> type as the other.
>
> Here:
>  - if one operand is a RawByteString use the (static or dynamic) 
> encoding of the other.
>  - if both are RawByteStrings use the dynamic encoding use the dynamic 
> encoding of one of them (supposedly this is no alternate case to before)
>
> If the conversion library sees a dynamic encoding type of $FFFF for 
> either source or target it will fail and issue an exception.

See my previously sent answer...

Regards,
Sven