Function ordinal_abbreviation 

pub fn ordinal_abbreviation(value: i64, plural: bool) -> &'static str

The letters written after a number to make it an ordinal, st, nd, rd or th, with an s after all but st for plural: music21’s ordinalAbbreviation.

use music21::common::numbertools::ordinal_abbreviation;

assert_eq!(ordinal_abbreviation(3, false), "rd");
assert_eq!(ordinal_abbreviation(12, false), "th");
assert_eq!(ordinal_abbreviation(255, true), "ths");