[Mesa-dev] [PATCH v2 09/29] mesa: Add _mesa_swap2_copy and _mesa_swap4_copy

[Brian Paul]

On 12/01/2014 04:05 AM, Iago Toral Quiroga wrote:
> We have _mesa_swap{2,4} but these do in-place byte-swapping only. The new
> functions receive an extra parameter so we can swap bytes on a source
> input array and store the results in a (possibly different) destination
> array.
>
> This is useful to implement byte-swapping in pixel uploads, since in this
> case we need to swap bytes on the src data which is owned by the
> application so we can't do an in-place byte swap.
> ---
>   src/mesa/main/image.c | 25 +++++++++++++++++--------
>   src/mesa/main/image.h | 10 ++++++++--
>   2 files changed, 25 insertions(+), 10 deletions(-)
>
> diff --git a/src/mesa/main/image.c b/src/mesa/main/image.c
> index 4ea5f04..9ad97c5 100644
> --- a/src/mesa/main/image.c
> +++ b/src/mesa/main/image.c
> @@ -41,36 +41,45 @@
>
>
>   /**
> - * Flip the order of the 2 bytes in each word in the given array.
> + * Flip the order of the 2 bytes in each word in the given array (src) and
> + * store the result in another array (dst). For in-place byte-swapping this
> + * function can be called with the same array for src and dst.
>    *
> - * \param p array.
> + * \param dst the array where byte-swapped data will be stored.
> + * \param src the array with the source data we want to byte-swap.
>    * \param n number of words.
>    */
>   void
> -_mesa_swap2( GLushort *p, GLuint n )
> +_mesa_swap2_copy( GLushort *dst, GLushort *src, GLuint n )
>   {
>      GLuint i;
>      for (i = 0; i < n; i++) {
> -      p[i] = (p[i] >> 8) | ((p[i] << 8) & 0xff00);
> +      dst[i] = (src[i] >> 8) | ((src[i] << 8) & 0xff00);
>      }
>   }
>
>
>
>   /*
> - * Flip the order of the 4 bytes in each word in the given array.
> + * Flip the order of the 4 bytes in each word in the given array (src) and
> + * store the result in another array (dst). For in-place byte-swapping this
> + * function can be called with the same array for src and dst.
> + *
> + * \param dst the array where byte-swapped data will be stored.
> + * \param src the array with the source data we want to byte-swap.
> + * \param n number of words.
>    */
>   void
> -_mesa_swap4( GLuint *p, GLuint n )
> +_mesa_swap4_copy( GLuint *dst, GLuint *src, GLuint n )
>   {
>      GLuint i, a, b;
>      for (i = 0; i < n; i++) {
> -      b = p[i];
> +      b = src[i];
>         a =  (b >> 24)
>   	| ((b >> 8) & 0xff00)
>   	| ((b << 8) & 0xff0000)
>   	| ((b << 24) & 0xff000000);
> -      p[i] = a;
> +      dst[i] = a;
>      }
>   }
>
> diff --git a/src/mesa/main/image.h b/src/mesa/main/image.h
> index abd84bf..79c6e68 100644
> --- a/src/mesa/main/image.h
> +++ b/src/mesa/main/image.h
> @@ -33,10 +33,16 @@ struct gl_context;
>   struct gl_pixelstore_attrib;
>
>   extern void
> -_mesa_swap2( GLushort *p, GLuint n );
> +_mesa_swap2_copy( GLushort *dst, GLushort *src, GLuint n );
>
>   extern void
> -_mesa_swap4( GLuint *p, GLuint n );
> +_mesa_swap4_copy( GLuint *dst, GLuint *src, GLuint n );
> +
> +static inline void
> +_mesa_swap2( GLushort *p, GLuint n ) { _mesa_swap2_copy(p, p, n); }

I'd prefer to see these functions formatted normally:

static inline void
_mesa_swap2(GLushort *p, GLuint n)
{
    _mesa_swap2_copy(p, p, n);
}


> +
> +static inline void
> +_mesa_swap4( GLuint *p, GLuint n ) { _mesa_swap4_copy(p, p, n); }
>
>   extern GLintptr
>   _mesa_image_offset( GLuint dimensions,
>