Function _round_to_exponent

Lib/fractions.py:73–99

Round a rational number to the nearest multiple of a given power of 10. Rounds the rational number n/d to the nearest integer multiple of 10**exponent, rounding to the nearest even integer multiple in the case of a tie. Returns a pair (sign: bool, significand: int) representing the

(n, d, exponent, no_neg_zero=False)

# Helpers for formatting

def _round_to_exponent(n, d, exponent, no_neg_zero=False):
    """Round a rational number to the nearest multiple of a given power of 10.

    Rounds the rational number n/d to the nearest integer multiple of
    10**exponent, rounding to the nearest even integer multiple in the case of
    a tie. Returns a pair (sign: bool, significand: int) representing the
    rounded value (-1)**sign * significand * 10**exponent.

    If no_neg_zero is true, then the returned sign will always be False when
    the significand is zero. Otherwise, the sign reflects the sign of the
    input.

    d must be positive, but n and d need not be relatively prime.
    """
    if exponent >= 0:
        d *= 10**exponent
    else:
        n *= 10**-exponent

    # The divmod quotient is correct for round-ties-towards-positive-infinity;
    # In the case of a tie, we zero out the least significant bit of q.
    q, r = divmod(n + (d >> 1), d)
    if r == 0 and d & 1 == 0:
        q &= -2

    sign = q < 0 if no_neg_zero else n < 0
    return sign, abs(q)


def _round_to_figures(n, d, figures):