17 Language support library [language.support]

17.3 Implementation properties [support.limits]

17.3.3 Floating-point type properties [fp.style]

17.3.3.1 Type float_­round_­style [round.style]

namespace std {
  enum float_round_style {
    round_indeterminate       = -1,
    round_toward_zero         =  0,
    round_to_nearest          =  1,
    round_toward_infinity     =  2,
    round_toward_neg_infinity =  3
  };
}
The rounding mode for floating-point arithmetic is characterized by the values: