David Adam : d3dx8: Implement D3DXQuaternionInverse.

[David.Adam at math.cnrs.fr]

Robert Shearman <rob at codeweavers.com> a écrit :

> Alexandre Julliard wrote:
>>  /*_________________D3DXQUATERNION________________*/
>> -D3DXQUATERNION* WINAPI D3DXQuaternionMultiply(D3DXQUATERNION *  
>> pout, CONST D3DXQUATERNION *pq1, CONST D3DXQUATERNION * pq2)
>> +D3DXQUATERNION* WINAPI D3DXQuaternionInverse(D3DXQUATERNION *pout,  
>> CONST D3DXQUATERNION *pq)
>> +{
>> +    D3DXQUATERNION temp;
>> +    FLOAT norm;
>> +
>> +    norm = D3DXQuaternionLengthSq(pq);
>> +    if ( !norm )
>> +    {
>> +     pout->x = 0.0f;
>> +     pout->y = 0.0f;
>> +     pout->z = 0.0f;
>> +     pout->w = 0.0f;
>> +    }
>> +    else
>> +    {
>> +    D3DXQuaternionConjugate(&temp, pq);
>> +    pout->x = temp.x / norm;
>> +    pout->y = temp.y / norm;
>> +    pout->z = temp.z / norm;
>> +    pout->w = temp.w / norm;
>> +    }
>> +    return pout;
>> +}
>> +
>> +D3DXQUATERNION* WINAPI D3DXQuaternionMultiply(D3DXQUATERNION  
>> *pout, CONST D3DXQUATERNION *pq1, CONST D3DXQUATERNION *pq2)
>> {
>>     pout->x = pq2->w * pq1->x + pq2->x * pq1->w + pq2->y * pq1->z -  
>> pq2->z * pq1->y;
>>     pout->y = pq2->w * pq1->y - pq2->x * pq1->z + pq2->y * pq1->w +  
>> pq2->z * pq1->x;
>
> This change causes the following warnings for me:
> math.c: In function ‘D3DXQuaternionInverse’:
> math.c:695: warning: ‘temp.x’ may be used uninitialised in this function
> math.c:695: warning: ‘temp.y’ may be used uninitialised in this function
> math.c:695: warning: ‘temp.z’ may be used uninitialised in this function
> math.c:695: warning: ‘temp.w’ may be used uninitialised in this function
>
> $ gcc --version
> gcc (GCC) 4.0.3 (Ubuntu 4.0.3-1ubuntu5)
> Copyright (C) 2006 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions. There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>
> I believe that this is causes by D3DXQuaternionConjugate not writing  
> to temp in one case (pq being NULL) and the compiler not recognising  
> that this case is already covered by the !norm branch above, since  
> D3DXQuaternionLengthSq will return 0.0f if pq is NULL.
>
> The attached patch works around the warning. However, there are  
> currently no tests for the case of pq being NULL so I don't know  
> whether it is correct.
>
> -- 
> Rob Shearman

I have just tried with a native d3dx8 dll. Giving a null pointer to pq  
leads to a crash. So, the application must take care to not send such  
a pointer.
So, I think that to avoid the warning that you see, we could just  
initialize the variable temp before the if condition.

David