From: Yaowu Xu <yaowu@google.com>
Date: Wed, 12 Oct 2011 17:49:49 +0000 (-0700)
Subject: fixed the wrong rounding in inverse haar transform
X-Git-Tag: v1.3.0~1217^2~380^2~184
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=152ce6b2b901279d1154ef45e8b387eb23cad3a0;p=libvpx

fixed the wrong rounding in inverse haar transform

Given the current forward haar transform:
 f0 = I0 + I1 + I2 + I3
 f1 = I0 + I1 - I2 - I3
 f2 = I0 - I1 + I2 - I3
 f3 = I0 - I1 - I2 + I3
the output of the inverse haar prior rounding:
 i0 = f0 + f1 + f2 + f3 = I0 * 4;
 i1 = f0 + f1 - f2 - f3 = I1 * 4;
 i2 = f0 - f1 + f2 - f3 = I2 * 4;
 i3 = f0 - f1 - f2 + f3 = I3 * 4;
As all the numbers are 4 multiples, simply >>2 always produces prefect
results in term of forward-inverse transform round trip error.

Change-Id: Id6658b00ea819ee61cfeef8c5985d4cd3e77f44e
---

diff --git a/vp8/common/idctllm.c b/vp8/common/idctllm.c
index 4f3a01b1b..567aa1dcc 100644
--- a/vp8/common/idctllm.c
+++ b/vp8/common/idctllm.c
@@ -512,14 +512,10 @@ void vp8_short_ihaar2x2_c(short *input, short *output, int pitch)
        op[i] = 0;
    }
 
-   x = (ip[0] + ip[1] + ip[4] + ip[8]);
-   op[0] = (x>=0?x+1:x-1)>>2;
-   x = (ip[0] - ip[1] + ip[4] - ip[8]);
-   op[1] = (x>=0?x+1:x-1)>>2;
-   x = (ip[0] + ip[1] - ip[4] - ip[8]);
-   op[4] = (x>=0?x+1:x-1)>>2;
-   x = (ip[0] - ip[1] - ip[4] + ip[8]);
-   op[8] = (x>=0?x+1:x-1)>>2;
+   op[0] = (ip[0] + ip[1] + ip[4] + ip[8])>>2;
+   op[1] = (ip[0] - ip[1] + ip[4] - ip[8])>>2;
+   op[4] = (ip[0] + ip[1] - ip[4] - ip[8])>>2;
+   op[8] = (ip[0] - ip[1] - ip[4] + ip[8])>>2;
 }
 
 void vp8_short_ihaar2x2_1_c(short *input, short *output, int pitch)
@@ -527,7 +523,7 @@ void vp8_short_ihaar2x2_1_c(short *input, short *output, int pitch)
    int a1;
    short *ip = input;
    short *op = output;
-   a1 = ((ip[0]>=0?ip[0]+1:ip[0]-1) >> 2);
+   a1 = ip[0]>> 2;
    op[0] = a1;
    op[2] = a1;
    op[8] = a1;