18 Language support library [language.support]

18.3 Implementation properties [support.limits]

18.3.2 Numeric limits [limits]

18.3.2.5 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:

(1.1)
round_indeterminate if the rounding style is indeterminable
(1.2)
round_toward_zero if the rounding style is toward zero
(1.3)
round_to_nearest if the rounding style is to the nearest representable value
(1.4)
round_toward_infinity if the rounding style is toward infinity
(1.5)
round_toward_neg_infinity if the rounding style is toward negative infinity