[][src]Crate fraction

Fraction is designed to be a precise lossless drop-in replacement for floating types (f32, f64).

It comes with a number of predefined type aliases covering the most common use cases such as Fraction, Decimal, BigFraction, DynaDecimal and so on (see prelude module for more examples).

The public API provides you with the generic types that you may use straightforwardly to build your own types, suiting your needs best (see prelude module for the examples).

Library features

  • Drop in replacement for floats with the exception for NaN == NaN so that it's hashable
  • It's hashable, so may be used as values in Sets and keys in dictionaries and hash maps
  • Display implementation for fractions and decimals
  • Fraction type, representing fractions
  • Decimal type, based on Fraction type represents floats as lossless decimals
  • DynaInt implements dinamically growing integer type that perfarms checked math and avoids stack overflows
  • PostgreSQL binary protocol integration for both fractions and decimals
  • Juniper support for both fractions and decimals
  • Generic integer conversions, such as i8 -> u8, usize -> u8 and so on
  • Lossless division with no allocations and infinite precision


Even though we do our best to keep it well covered with tests, there may be bugs out there. The library API is still in flux. When it gets stable we will release the version 1.0.0. You may find more info about Semantic Versioning on https://semver.org/. Bug reports and contributions are appreciated.

Crate features

  • with-bigint (default) integration with num::BigInt and num::BigUint data types
  • with-decimal (default) Decimal type implemented upon GenericFraction
  • with-dynaint (default) dynamically growing integer avoiding stack overflows
  • with-juniper-support Juniper integration
  • with-postgres-support PostgreSQL integration; Numeric/Decimal type
  • with-serde-support Serde traits implementation


Basic math implemented upon the num crate (in particular the num::rational module). The utilised traits from the num crate are re-exported, so you don't have to explicitly depend on that crate however, you may import them from either of crates if necessary.


To start using the library look no further than Prelude module.


Simple Fraction use:

type F = fraction::Fraction;

let result = F::from(0.7) / F::from(0.4);
assert_eq!(format!("{}", result), "7/4");
assert_eq!(format!("{:.2}", result), "1.75");
assert_eq!(format!("{:#.3}", result), "1.750");

Simple Decimal use:

type D = fraction::Decimal;

let result = D::from(0.5) / D::from(0.3);
assert_eq!(format!("{:.4}", result), "1.6666");

Generic integer conversion

use fraction::{Sign, GenericFraction};

type F = GenericFraction<u32>;

let fra = F::new_generic(Sign::Plus, 1i8, 42usize).unwrap();
assert_eq!(fra, F::new(1u32, 42u32));

Postgres usage

Postgres uses i16 for its binary protocol, so you'll have to use at least u16 as the base type for fractions/decimals. Otherwise you may workaround with DynaInt<u8, something_more_than_u8>. The safest way to go with would be DynaInt based types such as DynaFraction or DynaDecimal as they would prevent stack overflows for high values.

Beware bad numbers such as 1/3, 1/7. Fraction keeps the highest achievable precision (up to 16383 digits after floating point). Decimal uses its own precision. So, if you may end up with bad numbers, it may be preferable to go with Decimals over Fractions.

Both types (fractions and decimals) should work transparently in accordance with Postgres crate documentation


pub use self::prelude::*;



Optimistic type conversion


Implementation of fmt::Display for GenericFraction and Sign structures


Lossless integer division


Dynamic unsigned integer type selection


Crate error types


Integer generic traits and operations


Juniper values conversion for GenericFraction The format is case sensitive text representation of the sign and numbers. Those are:


Predefines some types for the most common use cases



A big signed integer type.


A big unsigned integer type.


Represents the ratio between two numbers.



Generic implementation of the fraction type


Sign representation



Numbers which have upper and lower bounds


Performs addition that returns None instead of wrapping around on overflow.


Performs division that returns None instead of panicking on division by zero and instead of wrapping around on underflow and overflow.


Performs multiplication that returns None instead of wrapping around on underflow or overflow.


Performs subtraction that returns None instead of wrapping around on underflow.


The base trait for numeric types, covering 0 and 1 values, comparisons, basic numeric operations, and string conversion.


Defines a multiplicative identity element for Self.


Useful functions for signed numbers (i.e. numbers that can be negative).


A generic trait for converting a value to a number.


Defines an additive identity element for Self.