[Libreoffice-commits] core.git: editeng: Eliminate unecessary padding in classes

Stephan Bergmann sbergman at redhat.com
Wed Nov 4 02:53:14 PST 2015

On 11/04/2015 11:21 AM, Norbert Thiebaud wrote:
> On Wed, Nov 4, 2015 at 3:42 AM, Stephan Bergmann <sbergman at redhat.com> wrote:
>> On 11/04/2015 09:16 AM, Daniel Robertson wrote:
>>>    class EDITENG_DLLPUBLIC SvxLRSpaceItem : public SfxPoolItem
>>>    {
>>> -    short   nFirstLineOfst;     // First-line indent _always_ relative to
>>> nTxtLeft
>>>        long    nTxtLeft;           // We spend a sal_uInt16
>>>        long    nLeftMargin;        // nLeft or the negative first-line
>>> indent
>>>        long    nRightMargin;       // The unproblematic right edge
>>>        sal_uInt16  nPropFirstLineOfst, nPropLeftMargin, nPropRightMargin;
>>> +    short   nFirstLineOfst;     // First-line indent _always_ relative to
>>> nTxtLeft
>> With micro-optimization changes like these, I would leave it to some domain
>> expert to decide whether it is actually worth it (i.e., whether on the one
>> hand the existing member order had been chosen deliberately, to aid human
>> comprehension, and whether on the other hand enough instances of that class
>> are created to warrant any such optimization).
> Domain expert are the last one to reliably evaluate 'human
> comprehension", since they _are_ domain expert
> wrt to the number of instance... even if there is only one. is it a
> reason to be sloppy ?

What is sloppy about a set of members sorted due to some rationale?  (I 
do not argue whether or not the members in this specific case were 
sorted due to such a rationale.  I just want to avoid such random 
micro-space-optimizations in the future to break well-founded orders.)

>>>        bool        bAutoFirst  : 1;    // Automatic calculation of the
>>> first line indent
>>> -    bool        bExplicitZeroMarginValRight;
>>> -    bool        bExplicitZeroMarginValLeft;
>>> +    bool        bExplicitZeroMarginValRight : 1;
>>> +    bool        bExplicitZeroMarginValLeft : 1;
>> It is unclear whether that is an optimization or a pessimization.
> you can choose size or perf.. but having a
> bool foo:1
> followed by 2 plain bool
> is wrong either way.

Yes, that is arguably something to clean up.  The question is just which 
way to clean it up makes more sense.  (Especially as a series of three 
non-bitfield bool can be a performance optimization over a series of 
three size-1-bitfield bool without being a space pessimization.)

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