ssse3: Add iterator for separable bilinear scaling

This new iterator uses the SSSE3 instructions pmaddubsw and pabsw to
implement a fast iterator for bilinear scaling.

There is a graph here recording the per-pixel time for various
bilinear scaling algorithms as reported by scaling-bench:

    http://people.freedesktop.org/~sandmann/ssse3.v2/ssse3.v2.png

As the graph shows, this new iterator is clearly faster than the
existing C iterator, and when used with an SSE2 combiner, it is also
faster than the existing SSE2 fast paths for upscaling, though not for
downscaling.

Another graph:

    http://people.freedesktop.org/~sandmann/ssse3.v2/movdqu.png

shows the difference between writing to iter->buffer with movdqa,
movdqu on an aligned buffer, and movdqu on a deliberately unaligned
buffer. Since the differences are very small, the patch here avoids
using movdqa because imposing alignment restrictions on iter->buffer
may interfere with other optimizations, such as writing directly to
the destination image.

The data was measured with scaling-bench on a Sandy Bridge Core
i3-2350M @ 2.3GHz and is available in this directory:

    http://people.freedesktop.org/~sandmann/ssse3.v2/

where there is also a Gnumeric spreadsheet ssse3.v2.gnumeric
containing the per-pixel values and the graph.

V2:
- Use uintptr_t instead of unsigned long in the ALIGN macro
- Use _mm_storel_epi64 instead of _mm_cvtsi128_si64 as the latter form
  is not available on x86-32.
- Use _mm_storeu_si128() instead of _mm_store_si128() to avoid
  imposing alignment requirements on iter->buffer

1 files changed, 312 insertions, 0 deletions

diff --git a/pixman/pixman-ssse3.c b/pixman/pixman-ssse3.c
index 19d71e7f..34763e20 100644
--- a/pixman/pixman-ssse3.c
+++ b/pixman/pixman-ssse3.c
@@ -35,6 +35,316 @@
 #include "pixman-private.h"
 #include "pixman-inlines.h"
 
+typedef struct
+{
+    int		y;
+    uint64_t *	buffer;
+} line_t;
+
+typedef struct
+{
+    line_t		line0;
+    line_t		line1;
+    pixman_fixed_t	y;
+    pixman_fixed_t	x;
+    uint64_t		data[1];
+} bilinear_info_t;
+
+static void
+ssse3_fetch_horizontal (bits_image_t *image, line_t *line,
+			int y, pixman_fixed_t x, pixman_fixed_t ux, int n)
+{
+    uint32_t *bits = image->bits + y * image->rowstride;
+    __m128i vx = _mm_set_epi16 (
+	- (x + 1), x, - (x + 1), x,
+	- (x + ux + 1), x + ux,  - (x + ux + 1), x + ux);
+    __m128i vux = _mm_set_epi16 (
+	- 2 * ux, 2 * ux, - 2 * ux, 2 * ux,
+	- 2 * ux, 2 * ux, - 2 * ux, 2 * ux);
+    __m128i vaddc = _mm_set_epi16 (1, 0, 1, 0, 1, 0, 1, 0);
+    __m128i *b = (__m128i *)line->buffer;
+    __m128i vrl0, vrl1;
+
+    while ((n -= 2) >= 0)
+    {
+	__m128i vw, vr, s;
+
+	vrl1 = _mm_loadl_epi64 (
+	    (__m128i *)(bits + pixman_fixed_to_int (x + ux)));
+	/* vrl1: R1, L1 */
+
+    final_pixel:
+	vrl0 = _mm_loadl_epi64 (
+	    (__m128i *)(bits + pixman_fixed_to_int (x)));
+	/* vrl0: R0, L0 */
+
+	/* The weights are based on vx which is a vector of 
+	 *
+	 *    - (x + 1), x, - (x + 1), x,
+	 *          - (x + ux + 1), x + ux, - (x + ux + 1), x + ux
+	 *
+	 * so the 16 bit weights end up like this:
+	 *
+	 *    iw0, w0, iw0, w0, iw1, w1, iw1, w1
+	 *
+	 * and after shifting and packing, we get these bytes:
+	 *
+	 *    iw0, w0, iw0, w0, iw1, w1, iw1, w1,
+	 *        iw0, w0, iw0, w0, iw1, w1, iw1, w1,
+	 *
+	 * which means the first and the second input pixel 
+	 * have to be interleaved like this:
+	 *
+	 *    la0, ra0, lr0, rr0, la1, ra1, lr1, rr1,
+	 *        lg0, rg0, lb0, rb0, lg1, rg1, lb1, rb1
+	 *
+	 * before maddubsw can be used.
+	 */
+
+	vw = _mm_add_epi16 (
+	    vaddc, _mm_srli_epi16 (vx, 16 - BILINEAR_INTERPOLATION_BITS));
+	/* vw: iw0, w0, iw0, w0, iw1, w1, iw1, w1
+	 */
+
+	vw = _mm_packus_epi16 (vw, vw);
+	/* vw: iw0, w0, iw0, w0, iw1, w1, iw1, w1,
+	 *         iw0, w0, iw0, w0, iw1, w1, iw1, w1
+	 */
+	vx = _mm_add_epi16 (vx, vux);
+
+	x += 2 * ux;
+
+	vr = _mm_unpacklo_epi16 (vrl1, vrl0);
+	/* vr: rar0, rar1, rgb0, rgb1, lar0, lar1, lgb0, lgb1 */
+
+	s = _mm_shuffle_epi32 (vr, _MM_SHUFFLE (1, 0, 3, 2));
+	/* s:  lar0, lar1, lgb0, lgb1, rar0, rar1, rgb0, rgb1 */
+
+	vr = _mm_unpackhi_epi8 (vr, s);
+	/* vr: la0, ra0, lr0, rr0, la1, ra1, lr1, rr1,
+	 *         lg0, rg0, lb0, rb0, lg1, rg1, lb1, rb1
+	 */
+
+	vr = _mm_maddubs_epi16 (vr, vw);
+
+	/* When the weight is 0, the inverse weight is
+	 * 128 which can't be represented in a signed byte.
+	 * As a result maddubsw computes the following:
+	 *
+	 *     r = l * -128 + r * 0
+	 *
+	 * rather than the desired
+	 *
+	 *     r = l * 128 + r * 0
+	 *
+	 * We fix this by taking the absolute value of the
+	 * result.
+	 */
+	vr = _mm_abs_epi16 (vr);
+
+	/* vr: A0, R0, A1, R1, G0, B0, G1, B1 */
+	_mm_store_si128 (b++, vr);
+    }
+
+    if (n == -1)
+    {
+	vrl1 = _mm_setzero_si128();
+	goto final_pixel;
+    }
+
+    line->y = y;
+}
+
+static uint32_t *
+ssse3_fetch_bilinear_cover (pixman_iter_t *iter, const uint32_t *mask)
+{
+    pixman_fixed_t fx, ux;
+    bilinear_info_t *info = iter->data;
+    line_t *line0, *line1;
+    int y0, y1;
+    int32_t dist_y;
+    __m128i vw;
+    int i;
+
+    fx = info->x;
+    ux = iter->image->common.transform->matrix[0][0];
+
+    y0 = pixman_fixed_to_int (info->y);
+    y1 = y0 + 1;
+
+    line0 = &info->line0;
+    line1 = &info->line1;
+
+    if (line0->y != y0 || line1->y != y1)
+    {
+	if (line0->y == y1 || line1->y == y0)
+	{
+	    line_t tmp = *line0;
+	    *line0 = *line1;
+	    *line1 = tmp;
+	}
+
+	if (line0->y != y0)
+	{
+	    ssse3_fetch_horizontal (
+		&iter->image->bits, line0, y0, fx, ux, iter->width);
+	}
+
+	if (line1->y != y1)
+	{
+	    ssse3_fetch_horizontal (
+		&iter->image->bits, line1, y1, fx, ux, iter->width);
+	}
+    }
+
+    dist_y = pixman_fixed_to_bilinear_weight (info->y);
+    dist_y <<= (16 - BILINEAR_INTERPOLATION_BITS);
+
+    vw = _mm_set_epi16 (
+	dist_y, dist_y, dist_y, dist_y, dist_y, dist_y, dist_y, dist_y);
+
+    for (i = 0; i + 3 < iter->width; i += 4)
+    {
+	__m128i top0 = _mm_load_si128 ((__m128i *)(line0->buffer + i));
+	__m128i bot0 = _mm_load_si128 ((__m128i *)(line1->buffer + i));
+	__m128i top1 = _mm_load_si128 ((__m128i *)(line0->buffer + i + 2));
+	__m128i bot1 = _mm_load_si128 ((__m128i *)(line1->buffer + i + 2));
+	__m128i r0, r1, tmp, p;
+
+	r0 = _mm_mulhi_epu16 (
+	    _mm_sub_epi16 (bot0, top0), vw);
+	tmp = _mm_cmplt_epi16 (bot0, top0);
+	tmp = _mm_and_si128 (tmp, vw);
+	r0 = _mm_sub_epi16 (r0, tmp);
+	r0 = _mm_add_epi16 (r0, top0);
+	r0 = _mm_srli_epi16 (r0, BILINEAR_INTERPOLATION_BITS);
+	/* r0:  A0 R0 A1 R1 G0 B0 G1 B1 */
+	r0 = _mm_shuffle_epi32 (r0, _MM_SHUFFLE (2, 0, 3, 1));
+	/* r0:  A1 R1 G1 B1 A0 R0 G0 B0 */
+
+	r1 = _mm_mulhi_epu16 (
+	    _mm_sub_epi16 (bot1, top1), vw);
+	tmp = _mm_cmplt_epi16 (bot1, top1);
+	tmp = _mm_and_si128 (tmp, vw);
+	r1 = _mm_sub_epi16 (r1, tmp);
+	r1 = _mm_add_epi16 (r1, top1);
+	r1 = _mm_srli_epi16 (r1, BILINEAR_INTERPOLATION_BITS);
+	r1 = _mm_shuffle_epi32 (r1, _MM_SHUFFLE (2, 0, 3, 1));
+	/* r1: A3 R3 G3 B3 A2 R2 G2 B2 */
+
+	p = _mm_packus_epi16 (r0, r1);
+
+	_mm_storeu_si128 ((__m128i *)(iter->buffer + i), p);
+    }
+
+    while (i < iter->width)
+    {
+	__m128i top0 = _mm_load_si128 ((__m128i *)(line0->buffer + i));
+	__m128i bot0 = _mm_load_si128 ((__m128i *)(line1->buffer + i));
+	__m128i r0, tmp, p;
+
+	r0 = _mm_mulhi_epu16 (
+	    _mm_sub_epi16 (bot0, top0), vw);
+	tmp = _mm_cmplt_epi16 (bot0, top0);
+	tmp = _mm_and_si128 (tmp, vw);
+	r0 = _mm_sub_epi16 (r0, tmp);
+	r0 = _mm_add_epi16 (r0, top0);
+	r0 = _mm_srli_epi16 (r0, BILINEAR_INTERPOLATION_BITS);
+	/* r0:  A0 R0 A1 R1 G0 B0 G1 B1 */
+	r0 = _mm_shuffle_epi32 (r0, _MM_SHUFFLE (2, 0, 3, 1));
+	/* r0:  A1 R1 G1 B1 A0 R0 G0 B0 */
+
+	p = _mm_packus_epi16 (r0, r0);
+
+	if (iter->width - i == 1)
+	{
+	    *(uint32_t *)(iter->buffer + i) = _mm_cvtsi128_si32 (p);
+	    i++;
+	}
+	else
+	{
+	    _mm_storel_epi64 ((__m128i *)(iter->buffer + i), p);
+	    i += 2;
+	}
+    }
+    
+    info->y += iter->image->common.transform->matrix[1][1];
+
+    return iter->buffer;
+}
+
+static void
+ssse3_bilinear_cover_iter_fini (pixman_iter_t *iter)
+{
+    free (iter->data);
+}
+
+static void
+ssse3_bilinear_cover_iter_init (pixman_iter_t *iter, const pixman_iter_info_t *iter_info)
+{
+    int width = iter->width;
+    bilinear_info_t *info;
+    pixman_vector_t v;
+
+    /* Reference point is the center of the pixel */
+    v.vector[0] = pixman_int_to_fixed (iter->x) + pixman_fixed_1 / 2;
+    v.vector[1] = pixman_int_to_fixed (iter->y) + pixman_fixed_1 / 2;
+    v.vector[2] = pixman_fixed_1;
+
+    if (!pixman_transform_point_3d (iter->image->common.transform, &v))
+	goto fail;
+
+    info = malloc (sizeof (*info) + (2 * width - 1) * sizeof (uint64_t) + 64);
+    if (!info)
+	goto fail;
+
+    info->x = v.vector[0] - pixman_fixed_1 / 2;
+    info->y = v.vector[1] - pixman_fixed_1 / 2;
+
+#define ALIGN(addr)							\
+    ((void *)((((uintptr_t)(addr)) + 15) & (~15)))
+
+    /* It is safe to set the y coordinates to -1 initially
+     * because COVER_CLIP_BILINEAR ensures that we will only
+     * be asked to fetch lines in the [0, height) interval
+     */
+    info->line0.y = -1;
+    info->line0.buffer = ALIGN (&(info->data[0]));
+    info->line1.y = -1;
+    info->line1.buffer = ALIGN (info->line0.buffer + width);
+
+    iter->get_scanline = ssse3_fetch_bilinear_cover;
+    iter->fini = ssse3_bilinear_cover_iter_fini;
+
+    iter->data = info;
+    return;
+
+fail:
+    /* Something went wrong, either a bad matrix or OOM; in such cases,
+     * we don't guarantee any particular rendering.
+     */
+    _pixman_log_error (
+	FUNC, "Allocation failure or bad matrix, skipping rendering\n");
+    
+    iter->get_scanline = _pixman_iter_get_scanline_noop;
+    iter->fini = NULL;
+}
+
+static const pixman_iter_info_t ssse3_iters[] = 
+{
+    { PIXMAN_a8r8g8b8,
+      (FAST_PATH_STANDARD_FLAGS			|
+       FAST_PATH_SCALE_TRANSFORM		|
+       FAST_PATH_BILINEAR_FILTER		|
+       FAST_PATH_SAMPLES_COVER_CLIP_BILINEAR),
+      ITER_NARROW | ITER_SRC,
+      ssse3_bilinear_cover_iter_init,
+      NULL, NULL
+    },
+
+    { PIXMAN_null },
+};
+
 static const pixman_fast_path_t ssse3_fast_paths[] =
 {
     { PIXMAN_OP_NONE },
@@ -46,5 +356,7 @@ _pixman_implementation_create_ssse3 (pixman_implementation_t *fallback)
     pixman_implementation_t *imp =
 	_pixman_implementation_create (fallback, ssse3_fast_paths);
 
+    imp->iter_info = ssse3_iters;
+
     return imp;
 }