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

[Patrick Baggett]

On Tue, Nov 18, 2014 at 3:23 AM, Iago Toral Quiroga <itoral at igalia.com>
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.
>
>
If this is being split into an "in-place" and "different pointers" version,
I think using the "restrict" keyword would be useful here to improve the
performance. Then, the in-place one cannot be implemented as copy(p,p,n),
but the code isn't overly complicated.



> 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); }
> +
> +static inline void
> +_mesa_swap4( GLuint *p, GLuint n ) { _mesa_swap4_copy(p, p, n); }
>
>  extern GLintptr
>  _mesa_image_offset( GLuint dimensions,
> --
> 1.9.1
>
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> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
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