From 152ce6b2b901279d1154ef45e8b387eb23cad3a0 Mon Sep 17 00:00:00 2001
From: Yaowu Xu <yaowu@google.com>
Date: Wed, 12 Oct 2011 10:49:49 -0700
Subject: [PATCH] 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
---
vp8/common/idctllm.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/vp8/common/idctllm.c b/vp8/common/idctllm.c
index 4f3a01b1b2..567aa1dccd 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;
--
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