atan2(0, 0) = ???

[Frank J. Henigman]

The man page for atan2 explicitly states that atan2(0, 0) = 0.
However the following program outputs NaN.

#include <math.h>
main() { printf("%f\n", atan2(0.0, 0.0)); }

Which is wrong: the man page or atan2?
(I tried both libm and libm43 on a Personal Iris and a 4D.)
-- 
fjhenigman at watcgl.uwaterloo.ca                       Computer Graphics Lab
fjhenigman at watcgl.waterloo.edu   Frank J. Henigman   University of Waterloo
 ...!watmath!watcgl!fjhenigman                       Waterloo, Ontario, Canada