puzzled of the congestion control window of Scalable TCP

I am now doing something related to the STCP (Scalable TCP). By pringking the
dynamic snd_cwnd in linux (kernel 2.6.18) ,the result puzzled me . Theoryly,
if any congestion occurs, the snd_cwnd = snd_cwnd * 0.875,but I haven't got
the result I expected. The snd_cwnd changes like this :

snd_cwnd = 1 , snd_ssthresh = 2147483647
snd_cwnd = 2 , snd_ssthresh = 2147483647
snd_cwnd = 3, snd_ssthresh = 2147483647
......
snd_cwnd = 19022, snd_ssthresh = 2147483647      // keeping this value for
several ms 
snd_cwnd = 1769, snd_ssthresh = 16645        // congestion occurs 
snd_cwnd = 1770, snd_ssthresh = 16645                  
......

From the above data. when congestion occurs , snd_ssthresh = 16645 ~=~

19022*0.875=16626 corresponds  to the theory calculated result. no problems. 
but what is the mean of snd_cwnd = 1770? how this value is calculated .who
(where )calculated it ?


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