PVS-Studio warning V547 for Newton Game Dynamics

typedef unsigned long long dgUnsigned64;

dgUnsigned64 m_mantissa[DG_GOOGOL_SIZE];

dgGoogol::dgGoogol(dgFloat64 value)
  :m_sign(0)
  ,m_exponent(0)
{
  ....
  m_mantissa[0] = (dgInt64 (dgFloat64 (
                    dgUnsigned64(1)<<62) * mantissa));

  // it looks like GCC have problems with this
  dgAssert (m_mantissa[0] >= 0);
  ....
}

This suspicious code was found in Newton Game Dynamics project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression 'm_mantissa[0] >= 0' is always true. Unsigned type value is always >= 0. dggoogol.cpp 55

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