Floating-point cheat sheet for Rust
Floating-Point Types
Rust has IEEE 754 single precision (32-bit) and double precision (64-bit) types:
let x: f32 = 0.1; // 32-bit float let y: f64 = 0.1; // 64-bit float The default floating point type is f64:
let z = 0.1; // 64-bit float Decimal Types
Rust does not have a built-in decimal type. However, there are various crates which implement a decimal type such as rust_decimal. The rust_decimal crate implements a 128-bit limited-precision decimal type denoted by the keyword Decimal:
use rust_decimal::prelude::*; let a = Decimal::new(1, 1); // second param is the number of fractional digits let b = Decimal::new(2, 1); // a Decimal representing exactly 0.2 let c = a + b; // a Decimal representing exactly 0.3 How to Round
To get a string:
format!("{:.2}", 1.2399); // returns "1.24" format!("{:.3}", 1.2399); // returns "1.240" format!("{:.2}", 1.2); // returns "1.20" To print to standard output:
println!("{:.2}", 1.2399); // prints "1.24" The round method returns the nearest integer to a number. It uses the rounding mode “Round half away from zero,” and works with both f32 and f64 types.
let f: f64 = 3.3; let g: f64 = -3.3; f.round(); // returns 3.0 g.round(); // returns -3.0 The rust_decimal crate contains the round_dp method which uses the Banker’s rounding mode.
let pi = Decimal::from_str("3.1415926535897932384626433832").unwrap(); println!("{}", pi.round_dp(2).to_string()); // prints "3.14" The rust_decimal crate also contains the round_dp_with_strategy method which allows you to specify a rounding strategy:
let i = Decimal::from_str("1.25").unwrap(); println!( "{}", i.round_dp_with_strategy(1, RoundingStrategy::RoundDown) .to_string() ) // prints "1.2" Resources
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