[altq 1190] RED estimator code has bug?

[Hiroyuki KATO <hiro@nemoto.ecei.tohoku.ac.jp>]

Hello,

I'm reading altq_red.c source code.

In code estimating average queue length (altq_red.c line:698)

    avg += (qlen(q) << FP_SHIFT) - (avg >> rp->red_wshift);


Is this statement mistake?
I think that correct statement is  

    avg += ((qlen(q) << FP_SHIFT) - avg ) >> rp->red_shift;

because 'exponential weighted moving average' is expressed such as below.
	avg <-- (1-w)*avg + w*qlen
	avg <-- avg + w*(qlen - avg)
	avg += w*(qlen - avg)

What do you think about this ?
Thanks.

---
Hiroyuki KATO
hiro@nemoto.ecei.tohoku.ac.jp