On 16/12/11 02:03, Ronald S. Bultje wrote:
From: "Ronald S. Bultje"<[email protected]>
For certain types of filters where the intermediate sum of coefficients
can go above the fixed-point equivalent of 1.0 in the middle of a filter,
the sum of a 31-bit calculation can overflow in both directions and can
thus not be represented in a 32-bit signed or unsigned integer. To work
around this, we subtract 0x40000000 from a signed integer base, so that
we're halfway signed/unsigned, which makes it fit even if it overflows.
After the filter finishes, we add the scaled bias back after a shift.
We use the same trick for 16-bit bpc YUV output routines.
---
Since I hate magic numbers w/out a name what about using
BIAS and BIAS_SHIFTED or something similar?
lu
--
Luca Barbato
Gentoo/linux
http://dev.gentoo.org/~lu_zero
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