Today I learned that NaNs and infinites may slow down programs significantly. So instead of

// some computation that produce NaN when arg == 0
if(arg == 0) // special case
    result = 0;

one should write

if(arg == 0)
    result = 0; // special case
else
    // some computation that produce NaN when arg == 0

Compare submission 19257027 and 19257693 and you'll see.