[FFmpeg-cvslog] SBR DSP: unroll sum_square

[Christophe GISQUET]

ffmpeg | branch: master | Christophe GISQUET <christophe.gisquet at gmail.com> | Wed Feb 22 17:48:59 2012 +0100| [dabf8dd34afdbb6dc9dc7603d7a5228fc67de4c8] | committer: Ronald S. Bultje

SBR DSP: unroll sum_square

The length is even, so some unrolling can be performed. Timings are for x86:
- 32bits: 102c -> 82c
- 64bits:  82c -> 69c

Signed-off-by: Ronald S. Bultje <rsbultje at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=dabf8dd34afdbb6dc9dc7603d7a5228fc67de4c8
---

 libavcodec/sbrdsp.c |   13 +++++++++----
 1 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/libavcodec/sbrdsp.c b/libavcodec/sbrdsp.c
index f942759..8c88fb3 100644
--- a/libavcodec/sbrdsp.c
+++ b/libavcodec/sbrdsp.c
@@ -35,13 +35,18 @@ static void sbr_sum64x5_c(float *z)
 
 static float sbr_sum_square_c(float (*x)[2], int n)
 {
-    float sum = 0.0f;
+    float sum0 = 0.0f, sum1 = 0.0f;
     int i;
 
-    for (i = 0; i < n; i++)
-        sum += x[i][0] * x[i][0] + x[i][1] * x[i][1];
+    for (i = 0; i < n; i += 2)
+    {
+        sum0 += x[i + 0][0] * x[i + 0][0];
+        sum1 += x[i + 0][1] * x[i + 0][1];
+        sum0 += x[i + 1][0] * x[i + 1][0];
+        sum1 += x[i + 1][1] * x[i + 1][1];
+    }
 
-    return sum;
+    return sum0 + sum1;
 }
 
 static void sbr_neg_odd_64_c(float *x)