rust/library/core/tests/fmt/float.rs

#[test]
fn test_format_f64() {
    assert_eq!("1", format!("{:.0}", 1.0f64));
    assert_eq!("9", format!("{:.0}", 9.4f64));
    assert_eq!("10", format!("{:.0}", 9.9f64));
    assert_eq!("9.8", format!("{:.1}", 9.849f64));
    assert_eq!("9.9", format!("{:.1}", 9.851f64));
    assert_eq!("1", format!("{:.0}", 0.5f64));
    assert_eq!("1.23456789e6", format!("{:e}", 1234567.89f64));
    assert_eq!("1.23456789e3", format!("{:e}", 1234.56789f64));
    assert_eq!("1.23456789E6", format!("{:E}", 1234567.89f64));
    assert_eq!("1.23456789E3", format!("{:E}", 1234.56789f64));
    assert_eq!("0.0", format!("{:?}", 0.0f64));
    assert_eq!("1.01", format!("{:?}", 1.01f64));

    let high_cutoff = 1e16_f64;
    assert_eq!("1e16", format!("{:?}", high_cutoff));
    assert_eq!("-1e16", format!("{:?}", -high_cutoff));
    assert!(!is_exponential(&format!("{:?}", high_cutoff * (1.0 - 2.0 * f64::EPSILON))));
    assert_eq!("-3.0", format!("{:?}", -3f64));
    assert_eq!("0.0001", format!("{:?}", 0.0001f64));
    assert_eq!("9e-5", format!("{:?}", 0.00009f64));
    assert_eq!("1234567.9", format!("{:.1?}", 1234567.89f64));
    assert_eq!("1234.6", format!("{:.1?}", 1234.56789f64));
}

#[test]
fn test_format_f32() {
    assert_eq!("1", format!("{:.0}", 1.0f32));
    assert_eq!("9", format!("{:.0}", 9.4f32));
    assert_eq!("10", format!("{:.0}", 9.9f32));
    assert_eq!("9.8", format!("{:.1}", 9.849f32));
    assert_eq!("9.9", format!("{:.1}", 9.851f32));
    assert_eq!("1", format!("{:.0}", 0.5f32));
    assert_eq!("1.2345679e6", format!("{:e}", 1234567.89f32));
    assert_eq!("1.2345679e3", format!("{:e}", 1234.56789f32));
    assert_eq!("1.2345679E6", format!("{:E}", 1234567.89f32));
    assert_eq!("1.2345679E3", format!("{:E}", 1234.56789f32));
    assert_eq!("0.0", format!("{:?}", 0.0f32));
    assert_eq!("1.01", format!("{:?}", 1.01f32));

    let high_cutoff = 1e16_f32;
    assert_eq!("1e16", format!("{:?}", high_cutoff));
    assert_eq!("-1e16", format!("{:?}", -high_cutoff));
    assert!(!is_exponential(&format!("{:?}", high_cutoff * (1.0 - 2.0 * f32::EPSILON))));
    assert_eq!("-3.0", format!("{:?}", -3f32));
    assert_eq!("0.0001", format!("{:?}", 0.0001f32));
    assert_eq!("9e-5", format!("{:?}", 0.00009f32));
    assert_eq!("1234567.9", format!("{:.1?}", 1234567.89f32));
    assert_eq!("1234.6", format!("{:.1?}", 1234.56789f32));
}

fn is_exponential(s: &str) -> bool {
    s.contains("e") || s.contains("E")
}