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//! [![github]](https://github.com/dtolnay/precise) [![crates-io]](https://crates.io/crates/precise) [![docs-rs]](https://docs.rs/precise)
//!
//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
//!
//! <br>
//!
//! Decimal representation of the single rational number whose value is
//! mathematically equal to the input float.
//!
//! Note that this is almost never an appropriate way to print user-facing
//! values. For that, use the [ryu] crate instead.
//!
//! [ryu]: https://github.com/dtolnay/ryu
//!
//! # Example
//!
//! ```
//! fn main() {
//! // 0.1000000000000000055511151231257827021181583404541015625
//! println!("{}", precise::to_string(0.1));
//! }
//! ```
#![doc(html_root_url = "https://docs.rs/precise/0.1.9")]
#![allow(
clippy::must_use_candidate,
clippy::needless_doctest_main,
clippy::redundant_else,
clippy::unseparated_literal_suffix
)]
use num_bigint::BigUint;
use num_traits::Pow;
pub fn to_string(n: impl traits::Float) -> String {
traits::Float::to_precise_string(n)
}
mod traits {
pub trait Float: Sized {
fn to_precise_string(n: Self) -> String;
}
impl Float for f32 {
fn to_precise_string(n: Self) -> String {
crate::f32_to_precise_string(n)
}
}
impl Float for f64 {
fn to_precise_string(n: Self) -> String {
crate::f64_to_precise_string(n)
}
}
}
fn f32_to_precise_string(n: f32) -> String {
if n.is_nan() {
return "NaN".to_owned();
}
if n.is_infinite() {
if n.is_sign_positive() {
return "inf".to_owned();
} else {
return "-inf".to_owned();
}
}
let bits = n.to_bits();
let is_negative = (bits & 0x8000_0000) != 0;
let biased_exponent = (bits & 0x7F80_0000) >> 23;
let significand = (bits & 0x007F_FFFF) + (1 << 23);
// value
// = significand * 2^(biased_exponent - 150)
// = significand * 2^biased_exponent * 5^150 / 10^150
let significand = BigUint::from(significand);
let two = BigUint::from(2u8);
let five = BigUint::from(5u8);
let numerator = significand * two.pow(biased_exponent) * five.pow(150u16);
let mut repr = numerator.to_string();
let more_zeros = 151usize.saturating_sub(repr.len());
let leading_zeros = "0".repeat(more_zeros);
repr = leading_zeros + &repr;
repr.insert(repr.len() - 150, '.');
repr.truncate(repr.trim_end_matches('0').len());
if repr.ends_with('.') {
repr.push('0');
}
if is_negative {
repr.insert(0, '-');
}
repr
}
fn f64_to_precise_string(n: f64) -> String {
if n.is_nan() {
return "NaN".to_owned();
}
if n.is_infinite() {
if n.is_sign_positive() {
return "inf".to_owned();
} else {
return "-inf".to_owned();
}
}
let bits = n.to_bits();
let is_negative = (bits & 0x8000_0000_0000_0000) != 0;
let biased_exponent = (bits & 0x7FF0_0000_0000_0000) >> 52;
let significand = (bits & 0x000F_FFFF_FFFF_FFFF) + (1 << 52);
// value
// = significand * 2^(biased_exponent - 1075)
// = significand * 2^biased_exponent * 5^1075 / 10^1075
let significand = BigUint::from(significand);
let two = BigUint::from(2u8);
let five = BigUint::from(5u8);
let numerator = significand * two.pow(biased_exponent) * five.pow(1075u16);
let mut repr = numerator.to_string();
let more_zeros = 1076usize.saturating_sub(repr.len());
let leading_zeros = "0".repeat(more_zeros);
repr = leading_zeros + &repr;
repr.insert(repr.len() - 1075, '.');
repr.truncate(repr.trim_end_matches('0').len());
if repr.ends_with('.') {
repr.push('0');
}
if is_negative {
repr.insert(0, '-');
}
repr
}