Mawk is the default Awk interpreter in Ubuntu 14.04

And it sux. Sad
Take this eg. ...
% echo '4001966552\n4001966552' | mawk '{sum+=$1; print $1 ", " sum}END{print sum; printf "%lu\n", sum}'
4001966552, 4.00197e+09
4001966552, 8.00393e+09
8.00393e+09
2147483647

It seems that Mawk is not capable of printing integer numbers larger than 2147483647. Shock I could not find any hint on what might be the reason for this, Google only spit out this original-mawk bug report. It contains some Mawk version information:
% ~/x/awk-build/mawk/build/awk/mawk -Wversion
mawk 1.3.4 20141206
Copyright 2008-2013,2014, Thomas E. Dickey
Copyright 1991-1996,2014, Michael D. Brennan

random-funcs:       srandom/random
regex-funcs:        internal
compiled limits:
sprintf buffer      8192
maximum-integer     2147483647

% /usr/bin/mawk -Wversion
mawk 1.3.3 Nov 1996, Copyright (C) Michael D. Brennan

compiled limits:
max NF             32767
sprintf buffer      2040

If I run the same, I get the latter ... i.e. mawk in Ubuntu 14.0.4 is still v1.3.3 (package version is: 1.3.3-17ubuntu2).
Looking through the package sources of Mawk 1.3.3-17ubuntu2 (for the string "integer") I could not find any hint on the 2147483647 limit.

If you run the same example in Gawk, you get what you expect:
% echo '4001966552\n4001966552' | gawk '{sum+=$1; print $1 ", " sum}END{print sum; printf "%lu\n", sum}'
4001966552, 4001966552
4001966552, 8003933104
8003933104
8003933104

So stick with Gawk. Smile

P.S.: I don't think that Mawk was the default Awk interpreter in Ubuntu. And this change most probabaly broke tons of Awk scripts (that relied on Gawk features not even knowing that those features were Gawk specific).