[PATCH] Faster unorm_to_unorm for wide processing.
Antti S. Lankila
alankila at bel.fi
Sun Jun 10 09:22:56 PDT 2012
Optimizing the unorm_to_unorm functions allows a speedup from:
src_8888_2x10 = L1: 62.08 L2: 60.73 M: 59.61 ( 4.30%) HT: 46.81
VT: 42.17 R: 43.18 RT: 26.01 (325Kops/s)
to:
src_8888_2x10 = L1: 76.94 L2: 78.43 M: 75.87 ( 5.59%) HT: 56.73
VT: 52.39 R: 53.00 RT: 29.29 (363Kops/s)
on a i7 Q720 -based laptop.
The key of the patch is the observation that unorm_to_unorm's work can
more easily be done with a simple multiplication and shift, when the
function is applied repeatedly and the parameters are not compile-time
constants. For instance, converting from 0xfe to 0xfefe (expanding
from 8 bits to 16 bits) can be done by calculating
c = c * 0x101
However, sometimes the result is not a neat replication of all the
bits. For instance, going from 10 bits to 16 bits can be done by
calculating
c = c * 0x401UL >> 4
where the intermediate result is 20 bit wide repetition of the 10-bit
pattern followed by shifting off the unnecessary lowest bits.
The patch has the algorithm to calculate the factor and the shift, and
converts the code to use it.
---
pixman/pixman-utils.c | 31 +++++++++++++++++++++++++++----
1 file changed, 27 insertions(+), 4 deletions(-)
diff --git a/pixman/pixman-utils.c b/pixman/pixman-utils.c
index 2ec2594..d0653e6 100644
--- a/pixman/pixman-utils.c
+++ b/pixman/pixman-utils.c
@@ -183,6 +183,22 @@ pixman_malloc_abc (unsigned int a,
return malloc (a * b * c);
}
+static void
+unorm_to_unorm_params (int inwidth, int outwidth, uint32_t *factor, int *shift)
+{
+ int w = 0;
+
+ *factor = 0;
+ while (inwidth != 0 && w < outwidth)
+ {
+ *factor |= 1 << w;
+ w += inwidth;
+ }
+
+ /* Did we generate too many bits? */
+ *shift = w - outwidth;
+}
+
/*
* This function expands images from ARGB8 format to ARGB16. To preserve
* precision, it needs to know the original source format. For example, if the
@@ -212,8 +228,15 @@ pixman_expand (uint64_t * dst,
r_mask = ~(~0 << r_size),
g_mask = ~(~0 << g_size),
b_mask = ~(~0 << b_size);
+ uint32_t au_factor, ru_factor, gu_factor, bu_factor;
+ int au_shift, ru_shift, gu_shift, bu_shift;
int i;
+ unorm_to_unorm_params (a_size, 16, &au_factor, &au_shift);
+ unorm_to_unorm_params (r_size, 16, &ru_factor, &ru_shift);
+ unorm_to_unorm_params (g_size, 16, &gu_factor, &gu_shift);
+ unorm_to_unorm_params (b_size, 16, &bu_factor, &bu_shift);
+
/* Start at the end so that we can do the expansion in place
* when src == dst
*/
@@ -226,7 +249,7 @@ pixman_expand (uint64_t * dst,
if (a_size)
{
a = (pixel >> a_shift) & a_mask;
- a16 = unorm_to_unorm (a, a_size, 16);
+ a16 = a * au_factor >> au_shift;
}
else
{
@@ -238,9 +261,9 @@ pixman_expand (uint64_t * dst,
r = (pixel >> r_shift) & r_mask;
g = (pixel >> g_shift) & g_mask;
b = (pixel >> b_shift) & b_mask;
- r16 = unorm_to_unorm (r, r_size, 16);
- g16 = unorm_to_unorm (g, g_size, 16);
- b16 = unorm_to_unorm (b, b_size, 16);
+ r16 = r * ru_factor >> ru_shift;
+ g16 = g * gu_factor >> gu_shift;
+ b16 = b * bu_factor >> bu_shift;
}
else
{
--
1.7.9.5
--------------020708070104080303070703--
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