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IEEE 754 rounding standard

Source: R/ieee-754.R
ieee-754.Rd

These functions implement the industry standard IEEE 754:

  • round_ties_to_even() rounds to the nearest value. If both are at equal distance, it tends to round to the even number (see base::round() for details).

  • round_ties_to_away() rounds to the nearest value. If both are at equal distance, it rounds to the number with the greater absolute value, i.e., the number that is further away from zero.

  • round_toward_positive() always rounds to the greater of the two nearest values. This is like ceiling at a given number of decimal places.

  • round_toward_negative() always rounds to the lesser of the two nearest values. This is like flooring at a given number of decimal places.

  • round_toward_zero() always rounds to the number with the lower absolute value, i.e., the number that is closer to zero. This is like truncation at a given number of decimal places.

Usage

round_ties_to_even(x, digits = 0, ...)

round_ties_to_away(x, digits = 0)

round_toward_positive(x, digits = 0)

round_toward_negative(x, digits = 0)

round_toward_zero(x, digits = 0)

Arguments

x

Numeric. The decimal number to round.

digits

Integer. Number of digits to round x to. Default is 0.

...

Only in round_ties_to_even(). Passed down to base::round().

Value

Numeric. x rounded to digits.

Details

The function names follow the official standard except for case conventions (IEEE 2019, pp. 27f.; the Wikipedia page is more accessible but uses slightly different names).

Internally, these functions are just wrappers around other roundwork functions as well as base::round(). They are presented here for easy compliance with the IEEE 754 standard in R.

References

IEEE (2019). IEEE Standard for Floating-Point Arithmetic. https://doi.org/10.1109/IEEESTD.2019.8766229

Examples

# Round to the nearest value. In case of a tie,
# the result is hard to predict but tends to be even:
round_ties_to_even(1.25, digits = 1)
#> [1] 1.2
round_ties_to_even(-1.25, digits = 1)
#> [1] -1.2

# Round to the nearest value. In case of a tie,
# round away from zero:
round_ties_to_away(1.25, digits = 1)
#> [1] 1.3
round_ties_to_away(-1.25, digits = 1)
#> [1] -1.3

# Always round to the greater value:
round_toward_positive(0.721, digits = 2)
#> [1] 0.73
round_toward_positive(-0.721, digits = 2)
#> [1] -0.72

# Always round to the lesser value:
round_toward_negative(3.249, digits = 2)
#> [1] 3.24
round_toward_negative(-3.249, digits = 2)
#> [1] -3.25

# Always round toward zero:
round_toward_zero(6.38, digits = 1)
#> [1] 6.3
round_toward_zero(-6.38, digits = 1)
#> [1] -6.3