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16bit IDWT implementation note

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Originally committed as revision 10396 to svn://svn.ffmpeg.org/ffmpeg/trunk
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Michael Niedermayer 2007-09-05 02:04:12 +00:00
parent c78fc717d9
commit 6a1aa752f0
1 changed files with 16 additions and 0 deletions
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doc/snow.txt
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@ -328,6 +328,22 @@ following are exactly identical
(3a)>>1 == a + (a>>1)
(a + 4b + 8)>>4 == ((a>>2) + b + 2)>>2
16bit implementation note:
The IDWT can be implemented with 16bits, but this requires some care to
prevent overflows, the following list, lists the minimum number of bits needed
for some terms
1. lifting step
A= s[i-1] + s[i+1] 16bit
3*A + 4 18bit
A + (A>>1) + 2 17bit
3. lifting step
s[i-1] + s[i+1] 17bit
4. lifiting step
3*(s[i-1] + s[i+1]) 17bit
TODO:
=====
Important: