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fixed the wrong rounding in inverse haar transform

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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
This commit is contained in:
Yaowu Xu 2011-10-12 10:49:49 -07:00
parent 3ca849691c
commit 152ce6b2b9
1 changed files with 5 additions and 9 deletions
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14
vp8/common/idctllm.c
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@ -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;