21 Language support library [language.support]

21.3 Implementation properties [support.limits]

21.3.3 Floating-point type properties [fp.style]

21.3.3.2 Type float_denorm_style [denorm.style]

namespace std {
  enum float_denorm_style {
    denorm_indeterminate = -1,
    denorm_absent = 0,
    denorm_present = 1
  };
}

The presence or absence of subnormal numbers (variable number of exponent bits) is characterized by the values:

(1.1)
denorm_indeterminate if it cannot be determined whether or not the type allows subnormal values
(1.2)
denorm_absent if the type does not allow subnormal values
(1.3)
denorm_present if the type does allow subnormal values