Function add_float_precision 

pub fn add_float_precision(
    value: FloatType,
    grain: FloatType,
) -> Option<OffsetQL>

The third or sixth a value is within grain of, as op_frac gives it, or nothing for a value near neither: music21’s addFloatPrecision, which leaves such a value alone.

use music21::common::numbertools::{add_float_precision, OffsetQL};

assert_eq!(
    add_float_precision(0.33, 1e-2),
    Some(OffsetQL::Fraction { numerator: 1, denominator: 3 })
);
assert_eq!(add_float_precision(0.2, 1e-2), None);