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prettyfloat.rs
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//! This module attempts to provide a %g formatter.
use std::fmt::{Alignment, Display, Formatter, Result};
/// Wrap this type around an `f64` in order to print it nicely.
pub struct PrettyFloat(pub f64);
fn n_decimals(value: f64, digits: usize) -> usize {
if value == 0. {
return 0;
}
let log10 = value.abs().log10();
if log10 > digits as f64 {
0
} else {
(digits as f64 - log10) as usize + 1
}
}
#[test]
fn test_n_decimals() {
assert_eq!(n_decimals(10.1, 1), 0);
assert_eq!(n_decimals(10.1, 2), 1);
assert_eq!(n_decimals(0.02, 1), 3);
assert_eq!(n_decimals(0.002, 1), 4);
}
fn cut_trailing(mut x: String) -> String {
if x.contains(".") {
if x.contains("e") {
let parts: Vec<_> = x.splitn(2, 'e').collect();
let mut x = parts[0].to_string();
while x.ends_with('0') {
x.pop();
}
if x.ends_with('.') {
x.pop();
}
x.push('e');
x.push_str(parts[1]);
x
} else {
while x.ends_with('0') {
x.pop();
}
if x.ends_with('.') {
x.pop();
}
x
}
} else {
x
}
}
impl Display for PrettyFloat {
fn fmt(&self, f: &mut Formatter) -> Result {
if let Some(precision) = f.precision() {
let ndec = n_decimals(self.0, precision);
let options = &[
cut_trailing(format!("{}", self.0)),
cut_trailing(format!("{:e}", self.0)),
cut_trailing(format!("{:.*}", ndec, self.0)),
cut_trailing(format!("{:.*e}", precision, self.0)),
];
let s = options.into_iter().min_by_key(|s| s.len()).unwrap();
if let Some(width) = f.width() {
// If we received a width, we use it
match f.align() {
Some(Alignment::Left) => write!(f, "{:<width$}", s, width = width),
Some(Alignment::Right) => write!(f, "{:>width$}", s, width = width),
Some(Alignment::Center) => write!(f, "{:^width$}", s, width = width),
None => write!(f, "{:width$}", s, width = width),
}
} else {
f.write_str(s)
}
} else {
let options = &[format!("{}", self.0), format!("{:e}", self.0)];
let s = options.into_iter().min_by_key(|s| s.len()).unwrap();
if let Some(width) = f.width() {
// If we received a width, we use it
match f.align() {
Some(Alignment::Left) => write!(f, "{:<width$}", s, width = width),
Some(Alignment::Right) => write!(f, "{:>width$}", s, width = width),
Some(Alignment::Center) => write!(f, "{:^width$}", s, width = width),
None => write!(f, "{:width$}", s, width = width),
}
} else {
f.write_str(s)
}
}
}
}
#[test]
fn known_numbers() {
println!("0.1 default");
assert_eq!(&format!("{}", PrettyFloat(0.1)), "0.1");
println!("0.1 prec=1");
assert_eq!(&format!("{:.1}", PrettyFloat(0.1)), "0.1");
println!("0.1 prec=2");
assert_eq!(&format!("{:.2}", PrettyFloat(0.1)), "0.1");
println!("0.1 prec=3");
assert_eq!(&format!("{:.3}", PrettyFloat(0.1)), "0.1");
println!("0.1 prec=4");
assert_eq!(&format!("{:.4}", PrettyFloat(0.1)), "0.1");
println!("0.1 prec=1 width width");
assert_eq!(&format!("{:5}", PrettyFloat(0.1)), "0.1 ");
assert_eq!(&format!("{:<5}", PrettyFloat(0.1)), "0.1 ");
assert_eq!(&format!("{:^5}", PrettyFloat(0.1)), " 0.1 ");
assert_eq!(&format!("{:>5}", PrettyFloat(0.1)), " 0.1");
println!("10.1");
assert_eq!(&format!("{}", PrettyFloat(10.1)), "10.1");
println!("10.1 prec 1");
assert_eq!(&format!("{:.1}", PrettyFloat(10.1)), "10");
println!("10.1 prec 2");
assert_eq!(&format!("{:.2}", PrettyFloat(10.1)), "10.1");
println!("10.1 prec 3");
assert_eq!(&format!("{:.3}", PrettyFloat(10.1)), "10.1");
println!("10.1 prec 4");
assert_eq!(&format!("{:.4}", PrettyFloat(10.1)), "10.1");
println!("1.11111111");
assert_eq!(&format!("{}", PrettyFloat(1.11111111)), "1.11111111");
println!("1.11111111 prec 1");
assert_eq!(&format!("{:.1}", PrettyFloat(1.11111111)), "1.1");
println!("1.11111111 prec 2");
assert_eq!(&format!("{:.2}", PrettyFloat(1.11111111)), "1.11");
println!("1.11111111 prec 3");
assert_eq!(&format!("{:.3}", PrettyFloat(1.11111111)), "1.111");
println!("1.11111111 prec 4");
assert_eq!(&format!("{:.4}", PrettyFloat(1.11111111)), "1.1111");
println!("1.00000000001");
assert_eq!(&format!("{}", PrettyFloat(1.00000000001)), "1.00000000001");
println!("1.11111111 prec 1");
assert_eq!(&format!("{:.1}", PrettyFloat(1.00000000001)), "1");
println!("1.11111111 prec 2");
assert_eq!(&format!("{:.2}", PrettyFloat(1.00000000001)), "1");
println!("1.11111111 prec 3");
assert_eq!(&format!("{:.3}", PrettyFloat(1.00000000001)), "1");
println!("1.11111111 prec 4");
assert_eq!(&format!("{:.4}", PrettyFloat(1.00000000001)), "1");
println!("1.00000000001e30");
assert_eq!(
&format!("{}", PrettyFloat(1.00000000001e30)),
"1.00000000001e30"
);
println!("1.11111111 prec 1");
assert_eq!(&format!("{:.1}", PrettyFloat(1.00000000001e30)), "1e30");
println!("1.11111111 prec 2");
assert_eq!(&format!("{:.2}", PrettyFloat(1.00000000001e30)), "1e30");
println!("1.11111111 prec 3");
assert_eq!(&format!("{:.3}", PrettyFloat(1.00000000001e30)), "1e30");
println!("1.11111111 prec 4");
assert_eq!(&format!("{:.4}", PrettyFloat(1.00000000001e30)), "1e30");
println!("1.11111111e200");
assert_eq!(
&format!("{}", PrettyFloat(1.11111111e200)),
"1.11111111e200"
);
println!("1.11111111 prec 1");
assert_eq!(&format!("{:.1}", PrettyFloat(1.11111111e200)), "1.1e200");
println!("1.11111111 prec 2");
assert_eq!(&format!("{:.2}", PrettyFloat(1.11111111e200)), "1.11e200");
println!("1.11111111 prec 3");
assert_eq!(&format!("{:.3}", PrettyFloat(1.11111111e200)), "1.111e200");
println!("1.11111111 prec 4");
assert_eq!(&format!("{:.4}", PrettyFloat(1.11111111e200)), "1.1111e200");
println!("1e200");
assert_eq!(&format!("{}", PrettyFloat(1e200)), "1e200");
println!("1e200 prec 1");
assert_eq!(&format!("{:.1}", PrettyFloat(1e200)), "1e200");
println!("1e200 prec 2");
assert_eq!(&format!("{:.2}", PrettyFloat(1e200)), "1e200");
println!("1e200 prec 3");
assert_eq!(&format!("{:.3}", PrettyFloat(1e200)), "1e200");
println!("1e200 prec 4");
assert_eq!(&format!("{:.4}", PrettyFloat(1e200)), "1e200");
}
#[test]
fn short_representation_with_prec() {
for &prec in &[1, 3, 6, 16, 30] {
println!("testing with {} digits", prec);
for &f in &[0.1_f64, 1e-100, 0.1111111111111111] {
println!(" testing {}", f);
shortest_with_prec(f, prec);
}
}
}
#[cfg(test)]
fn shortest_with_prec(f: f64, prec: usize) {
use std::str::FromStr;
println!(
"{:.prec$} {:.prec$} {:.prec$}",
f,
f,
PrettyFloat(f),
prec = prec
);
assert!(format!("{:.*}", prec, PrettyFloat(f)).len() <= format!("{:.*e}", prec, f).len());
if let Ok(fprec) = f64::from_str(&format!("{:.*}", prec, PrettyFloat(f))) {
assert!(((fprec - f) / f).abs() < 10_f64.powf(-(prec as f64)));
} else {
panic!("this is crazy talk!");
}
}
#[test]
fn short_representation() {
for &f in &[0.1_f64, 1e-100, 0.1111111111111111] {
shortest(f);
}
}
#[cfg(test)]
fn shortest(f: f64) {
use std::str::FromStr;
println!("{} {:e} {}", f, f, PrettyFloat(f));
assert!(format!("{}", PrettyFloat(f)).len() <= format!("{}", f).len());
assert!(format!("{}", PrettyFloat(f)).len() <= format!("{:e}", f).len());
assert_eq!(f64::from_str(&format!("{}", PrettyFloat(f))), Ok(f));
}