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