Hi, On Thu, Dec 15, 2011 at 8:10 PM, Luca Barbato <[email protected]> wrote:
> 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? > The values (not the 0x40000000, but the 0x10000) change per use depending on their use afterwards... So a macro doesn't help much. As long as it's commented, it should be OK. Ronald
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