[Mesa-dev] [PATCH][RFC] mesa/main: Clamp rgba with streamed sse

[Matt Turner]

On Fri, Oct 31, 2014 at 3:13 AM, Juha-Pekka Heikkila
<juhapekka.heikkila at gmail.com> wrote:
> Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com>
> ---
>  src/mesa/main/colormac.h      | 20 +++++++++++++++
>  src/mesa/main/pixeltransfer.c | 59 ++++++++++++++++++++++++++++++++-----------
>  2 files changed, 64 insertions(+), 15 deletions(-)
>
> diff --git a/src/mesa/main/colormac.h b/src/mesa/main/colormac.h
> index c8adca6..da5e094 100644
> --- a/src/mesa/main/colormac.h
> +++ b/src/mesa/main/colormac.h
> @@ -51,6 +51,26 @@ _mesa_unclamped_float_rgba_to_ubyte(GLubyte dst[4], const GLfloat src[4])
>
>
>  /**
> + * Clamp four float values to [min,max]
> + */
> +#if defined(__SSE2__) && defined(__GNUC__)
> +static inline void
> +_mesa_clamp_float_rgba(GLfloat src[4], GLfloat result[4], const float min,
> +                       const float max)
> +{
> +    __m128  operand, minval, maxval;
> +
> +    operand = _mm_loadu_ps(src);

Surely 128-bit pixels will be 128-bit aligned? I think we can use an
aligned load here.

> +    minval = _mm_set1_ps(min);
> +    maxval = _mm_set1_ps(max);
> +    operand = _mm_max_ps(operand, minval);
> +    operand = _mm_min_ps(operand, maxval);
> +    _mm_storeu_ps(result, operand);

And an aligned store here.

> +}
> +#endif
> +
> +
> +/**
>   * \name Generic color packing macros.  All inputs should be GLubytes.
>   *
>   * \todo We may move these into texstore.h at some point.
> diff --git a/src/mesa/main/pixeltransfer.c b/src/mesa/main/pixeltransfer.c
> index 8bbeeb8..e16eb59 100644
> --- a/src/mesa/main/pixeltransfer.c
> +++ b/src/mesa/main/pixeltransfer.c
> @@ -35,7 +35,7 @@
>  #include "pixeltransfer.h"
>  #include "imports.h"
>  #include "mtypes.h"
> -
> +#include "x86/common_x86_asm.h"
>
>  /*
>   * Apply scale and bias factors to an array of RGBA pixels.
> @@ -89,16 +89,34 @@ _mesa_map_rgba( const struct gl_context *ctx, GLuint n, GLfloat rgba[][4] )
>     const GLfloat *bMap = ctx->PixelMaps.BtoB.Map;
>     const GLfloat *aMap = ctx->PixelMaps.AtoA.Map;
>     GLuint i;
> -   for (i=0;i<n;i++) {
> -      GLfloat r = CLAMP(rgba[i][RCOMP], 0.0F, 1.0F);
> -      GLfloat g = CLAMP(rgba[i][GCOMP], 0.0F, 1.0F);
> -      GLfloat b = CLAMP(rgba[i][BCOMP], 0.0F, 1.0F);
> -      GLfloat a = CLAMP(rgba[i][ACOMP], 0.0F, 1.0F);
> -      rgba[i][RCOMP] = rMap[F_TO_I(r * rscale)];
> -      rgba[i][GCOMP] = gMap[F_TO_I(g * gscale)];
> -      rgba[i][BCOMP] = bMap[F_TO_I(b * bscale)];
> -      rgba[i][ACOMP] = aMap[F_TO_I(a * ascale)];
> +
> +#if defined(__SSE2__) && defined(__GNUC__)
> +   if (cpu_has_xmm2) {

#ifdef __SSE2__ means the compiler is free to use SSE2 instructions
whenever it pleases. That's not what you want here, if you're also
doing runtime checking (cpu_has_xmm2).

The typical way to do this is to put the function containing SSE
instructions in a separate file that is compiled with -msse2. See
streaming-load-memcpy.c for example. gcc has a way to mark specific
functions, but since we have to compile with MSVC...

I think you just want copy-and-paste the SSE4.1 testing code in
configure.ac for SSE2 and then wrap these uses in #ifdef USE_SSE2.

> +      for (i=0;i<n;i++) {
> +         GLfloat rgba_temp[4];
> +         _mesa_clamp_float_rgba(rgba[i], rgba_temp, 0.0F, 1.0F);
> +         rgba[i][RCOMP] = rMap[F_TO_I(rgba_temp[RCOMP] * rscale)];
> +         rgba[i][GCOMP] = gMap[F_TO_I(rgba_temp[GCOMP] * gscale)];
> +         rgba[i][BCOMP] = bMap[F_TO_I(rgba_temp[BCOMP] * bscale)];
> +         rgba[i][ACOMP] = aMap[F_TO_I(rgba_temp[ACOMP] * ascale)];

Oh, but we shouldn't be bothering to store the floats back to memory
anyway. We should just do this part with SSE as well.