Re: [Dev-C++] Optimizing C code, what is best??

[Per W. <pw...@ia...>]

Some sugestions:
1 - you are summing 16-bit numbers into 32-bit, but returning 64-bit.
2 - you are sending in wRow,wColFrom,wColTo as references, despite not
having any intention of sending back any change.
3 - you are using a lot of variables in the loop.
4 - you are using a lot of indexing in the loop.

A suggested change might be:

DWORD CMyClass::computeDistSquare(const short *src,
                                  const WORD wRow,
                                  const WORD wColFrom,const
                                  WORD wColTo) const
{
    DWORD dwDist2 = 0;
    int iA;
    short *sp = sData[wRow] + wColFrom;
    short *end = src + wColTo;
    src += wColFrom;
    while (src <= end) {
        iA = *src++ - *sp++;
        dwDist2 += iA*iA;
    }
    return dwDist2;
}

Now the loop uses 5 variables instead of 7 - each variable just 32-bit
large and fitting in a single register.

/Per W

On Fri, 30 May 2003, Zodiaq wrote:

> Hello All Dev-cpp-users,
>
>   there is one function in my program that needs some optimization...
> the problem is about computing distance between parts of two
> vectors... currently it is done like this:
>
> DWORD64 computeDistance( short *src, const WORD &wRow, const WORD
> &wColFrom, const WORD &wColTo ) const
>         {
>                 DWORD dwDist = 0;
>                 INT iA;
>                 short *sP = sData[ wRow ];
>                 for( WORD wCol = wColFrom; wCol <= wColTo; ++wCol )
>                 {
>                         iA = src[ wCol ] - sP[ wCol ];
>                         dwDist += iA * iA;
>                 }
>                 return dwDist;
>       }
>
> src is element I want to compute distance from specified element of
> big array of rows... gprof shows that this function takes over 90% of
> total program time...
>
> well, I know it is not about DevC++, but since I made progs under it
> and this is quite simple problem, I hope that someone can and will
> help me...
>
> The best solution for me would be ASM code optimized for AMD Athlon
> processor (for my computer, which as only one will run this code). For
> someone with good knowledge of ASM this is only few moments, and for
> me great deal of work - I don't know ASM a bit... so please someone
> help me... thank you in advance!
>
> --
> regards, Zodiaq...
>
>
>
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