bug#37241: large performance gap when start+inc specified with 'seq'

[L A Walsh]

Was looking at some large sequences and the time they took
and found that while end-point only was fast:

declare -x TIMEFORMAT="%2Rsec %2Uusr %2Ssys (%P%% cpu)"

> time seq 1e8 >/dev/null
0.75sec 0.74usr 0.01sys (99.77% cpu)

Trying just to generate only odd numbers:
> time seq 1 2 1e8 >/dev/null
24.70sec 24.64usr 0.01sys (99.82% cpu)

took way longer.

Shouldn't the 2nd case take about half as long as
the first?  They are both adding integers though in
2nd case, its skipping the "even"s on output.

If it was some floating point calculation needed, I might not
have blinked, but both an integer sequence with the 2nd
being half as long?  Should half the numbers take almost 33x
longer?