Re: [Devel] suggested improvement to FT_Add64

[David Turner]

Hello Graham,

Graham Asher a écrit :
> 
> This might be said to be nitpicking, but there is a small improvement to be
> made to FT_Add64, which might save a cycle or two:
> 
> replace
> 
>   FT_EXPORT_DEF( void )  FT_Add64( FT_Int64*  x,
>                                    FT_Int64*  y,
>                                    FT_Int64  *z )
>   {
>     register FT_UInt32  lo, hi;
> 
>     lo = x->lo + y->lo;
>     hi = x->hi + y->hi + ( lo < x->lo );
> 
>     z->lo = lo;
>     z->hi = hi;
>   }
> 
> with
> 
>   FT_EXPORT_DEF( void )  FT_Add64( FT_Int64*  x,
>                                    FT_Int64*  y,
>                                    FT_Int64  *z )
>   {
>     z->lo = x->lo + y->lo;
>     z->hi = x->hi + y->hi + (z->lo < x->lo );
>   }
> 
> There is no need for the local variables. Anything gained by the use of a
> local variable 'lo' instead of 'z->lo', which is used twice, would surely be
> lost by the extra assignments to 'lo' and 'z->lo'. And 'register' is
> irrelevant to modern compilers.
>

Graham, your code is _not_ equivalent to the original one.
Indeed, it will produce incorrect results when "z == x"..

Second, FreeType is only used with not so modern compilers in the
embedded market, and a "register" here is not going to cost you
anything for more recent ones anyway..

And any modern compiler is going to get rid of the "hi" local
variable anyway, so I don't think we need to optimize the hell
out of this code..

Regards,

- David