use of control87 and floating point underflow

In my c program if I put in the line
_control87(0, EM_ZERODIVIDE |_EM_UNDERFLOW);
I get a floating point underflow exception while running.

However if I change it to
_control87(EM_ZERODIVIDE |_EM_UNDERFLOW, EM_ZERODIVIDE |_EM_UNDERFLOW);
it runs fine.

Please help me undertsand whats wrong here and the correct use of
control87 function.

.

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