Re: [PATCH 3/3] usp10: Add support for format 2 pair adjustments.

[Dmitry Timoshkov]

Huw Davies  wrote:
> typedef struct {
> - WORD PosFormat;
> - WORD Coverage;
> - WORD ValueFormat1;
> - WORD ValueFormat2;
> - WORD ClassDef1;
> - WORD ClassDef2;
> - WORD Class1Count;
> - WORD Class2Count;
> - WORD Class1Record[1];
>
> +} GPOS_PairPosFormat2;

Shouldn't this structure be 2 bytes aligned?

[PATCH 3/3] usp10: Add support for format 2 pair adjustments.

[Huw Davies]

On Thu, Dec 20, 2012 at 10:12:38PM +0800, Dmitry Timoshkov wrote:
> Huw Davies  wrote:
> > typedef struct {
> > - WORD PosFormat;
> > - WORD Coverage;
> > - WORD ValueFormat1;
> > - WORD ValueFormat2;
> > - WORD ClassDef1;
> > - WORD ClassDef2;
> > - WORD Class1Count;
> > - WORD Class2Count;
> > - WORD Class1Record[1];
> >
> > +} GPOS_PairPosFormat2;
>
> Shouldn't this structure be 2 bytes aligned?

I don't see why.  They're all WORDs.

Huw.

[PATCH 3/3] usp10: Add support for format 2 pair adjustments.

[Dmitry Timoshkov]

Huw Davies  wrote:
> > > typedef struct {
> > > - WORD PosFormat;
> > > - WORD Coverage;
> > > - WORD ValueFormat1;
> > > - WORD ValueFormat2;
> > > - WORD ClassDef1;
> > > - WORD ClassDef2;
> > > - WORD Class1Count;
> > > - WORD Class2Count;
> > > - WORD Class1Record[1];
> > >
> > > +} GPOS_PairPosFormat2;
> >
> > Shouldn't this structure be 2 bytes aligned?
>
> I don't see why.  They're all WORDs.

There are 9 elements of 2 bytes in size each, 18 bytes in total,
the compiler will align this structure to 4 bytes, making its
size 20 bytes.

[PATCH 3/3] usp10: Add support for format 2 pair adjustments.

[Huw Davies]

On Thu, Dec 20, 2012 at 11:05:48PM +0800, Dmitry Timoshkov wrote:
> Huw Davies  wrote:
> > > > typedef struct {
> > > > - WORD PosFormat;
> > > > - WORD Coverage;
> > > > - WORD ValueFormat1;
> > > > - WORD ValueFormat2;
> > > > - WORD ClassDef1;
> > > > - WORD ClassDef2;
> > > > - WORD Class1Count;
> > > > - WORD Class2Count;
> > > > - WORD Class1Record[1];
> > > >
> > > > +} GPOS_PairPosFormat2;
> > >
> > > Shouldn't this structure be 2 bytes aligned?
> >
> > I don't see why.  They're all WORDs.
>
> There are 9 elements of 2 bytes in size each, 18 bytes in total,
> the compiler will align this structure to 4 bytes, making its
> size 20 bytes.

The size is irrelevant - it's variable sized anyway.  We just care
about the offsets of the elements.

[PATCH 3/3] usp10: Add support for format 2 pair adjustments.

[Dmitry Timoshkov]

Huw Davies  wrote:
> > There are 9 elements of 2 bytes in size each, 18 bytes in total,
> > the compiler will align this structure to 4 bytes, making its
> > size 20 bytes.
>
> The size is irrelevant - it's variable sized anyway.  We just care
> about the offsets of the elements.

Anyway, in order to avoid any confusion or bugs in future with allocating
an array of such structures or using sizeof() on them I'd suggest to
explicitely specify alignment.

[PATCH 3/3] usp10: Add support for format 2 pair adjustments.

[Huw Davies]

On Thu, Dec 20, 2012 at 11:26:36PM +0800, Dmitry Timoshkov wrote:
> Huw Davies  wrote:
> > The size is irrelevant - it's variable sized anyway.  We just care
> > about the offsets of the elements.
>
> Anyway, in order to avoid any confusion or bugs in future with allocating
> an array of such structures or using sizeof() on them I'd suggest to
> explicitely specify alignment.

Using an array of these structures or using sizeof() is wrong anyway
as they are variable-sized...

[PATCH 3/3] usp10: Add support for format 2 pair adjustments.

[Alexandre Julliard]

Dmitry Timoshkov  writes:
> There are 9 elements of 2 bytes in size each, 18 bytes in total,
> the compiler will align this structure to 4 bytes, making its
> size 20 bytes.

No it won't.