# Crate rust_decimal

Expand description

A Decimal number implementation written in pure Rust suitable for financial calculations that require significant integral and fractional digits with no round-off errors.

The binary representation consists of a 96 bit integer number, a scaling factor used to specify the decimal fraction and a 1 bit sign. Because of this representation, trailing zeros are preserved and may be exposed when in string form. These can be truncated using the `normalize` or `round_dp` functions.

### Installing

Using `cargo-edit`:

``````\$ cargo add rust_decimal
``````

In addition, if you would like to use the optimized macro for convenient creation of decimals:

``````\$ cargo add rust_decimal_macros
``````

Alternatively, you can edit your `Cargo.toml` directly and run `cargo update`:

``````[dependencies]
rust_decimal = "1.29"
rust_decimal_macros = "1.29"
``````

### Usage

Decimal numbers can be created in a few distinct ways. The easiest and most efficient method of creating a Decimal is to use the procedural macro within the `rust_decimal_macros` crate:

``````// Procedural macros need importing directly
use rust_decimal_macros::dec;

let number = dec!(-1.23) + dec!(3.45);
assert_eq!(number, dec!(2.22));
assert_eq!(number.to_string(), "2.22");``````

Alternatively you can also use one of the Decimal number convenience functions (see the docs for more details):

``````// Using the prelude can help importing trait based functions (e.g. core::str::FromStr).
use rust_decimal::prelude::*;

// Using an integer followed by the decimal points
let scaled = Decimal::new(202, 2);
assert_eq!("2.02", scaled.to_string());

// From a 128 bit integer
let balance = Decimal::from_i128_with_scale(5_897_932_384_626_433_832, 2);
assert_eq!("58979323846264338.32", balance.to_string());

// From a string representation
let from_string = Decimal::from_str("2.02").unwrap();
assert_eq!("2.02", from_string.to_string());

// From a string representation in a different base
assert_eq!("65535", from_string_base16.to_string());

// From scientific notation
let sci = Decimal::from_scientific("9.7e-7").unwrap();
assert_eq!("0.00000097", sci.to_string());

// Using the `Into` trait
let my_int: Decimal = 3_i32.into();
assert_eq!("3", my_int.to_string());

// Using the raw decimal representation
let pi = Decimal::from_parts(1_102_470_952, 185_874_565, 1_703_060_790, false, 28);
assert_eq!("3.1415926535897932384626433832", pi.to_string());``````

Once you have instantiated your `Decimal` number you can perform calculations with it just like any other number:

``````use rust_decimal::prelude::*;
use rust_decimal_macros::dec;

let amount = dec!(25.12);
let tax_percentage = dec!(0.085);
let total = amount + (amount * tax_percentage).round_dp(2);
assert_eq!(total, dec!(27.26));``````

### Features

Behavior / Functionality

Database

Serde

#### `borsh`

Enables Borsh serialization for `Decimal`.

#### `c-repr`

Forces `Decimal` to use `[repr(C)]`. The corresponding target layout is 128 bit aligned.

#### `db-postgres`

Enables a PostgreSQL communication module. It allows for reading and writing the `Decimal` type by transparently serializing/deserializing into the `NUMERIC` data type within PostgreSQL.

#### `db-tokio-postgres`

Enables the tokio postgres module allowing for async communication with PostgreSQL.

#### `db-diesel-postgres`

Enable `diesel` PostgreSQL support. By default, this enables version `1.4` of `diesel`. If you wish to use the `2.0` version of `diesel` then you can do so by using the feature `db-diesel2-postgres`. Please note, if both features are enabled then version 2 will supersede version 1.

#### `db-diesel-mysql`

Enable `diesel` MySQL support. By default, this enables version `1.4` of `diesel`. If you wish to use the `2.0` version of `diesel` then you can do so by using the feature `db-diesel2-mysql`. Please note, if both features are enabled then version 2 will supersede version 1.

#### `legacy-ops`

Warning: This is deprecated and will be removed from a future versions.

As of `1.10` the algorithms used to perform basic operations have changed which has benefits of significant speed improvements. To maintain backwards compatibility this can be opted out of by enabling the `legacy-ops` feature.

#### `maths`

The `maths` feature enables additional complex mathematical functions such as `pow`, `ln`, `enf`, `exp` etc. Documentation detailing the additional functions can be found on the `MathematicalOps` trait.

Please note that `ln` and `log10` will panic on invalid input with `checked_ln` and `checked_log10` the preferred functions to curb against this. When the `maths` feature was first developed the library would instead return `0` on invalid input. To re-enable this non-panicking behavior, please use the feature: `maths-nopanic`.

#### `ndarray`

Enables arithmetic operations using `ndarray` on arrays of `Decimal`.

#### `rand`

Implements `rand::distributions::Distribution<Decimal>` to allow the creation of random instances.

Note: When using `rand::Rng` trait to generate a decimal between a range of two other decimals, the scale of the randomly-generated decimal will be the same as the scale of the input decimals (or, if the inputs have different scales, the higher of the two).

#### `rkyv`

Enables rkyv serialization for `Decimal`. Supports rkyv’s safe API when the `rkyv-safe` feature is enabled as well.

#### `rocket-traits`

Enable support for Rocket forms by implementing the `FromFormField` trait.

#### `rust-fuzz`

Enable `rust-fuzz` support by implementing the `Arbitrary` trait.

#### `serde-float`

Note: it is recommended to use the `serde-with-*` features for greater control. This allows configurability at the data level.

Enable this so that JSON serialization of `Decimal` types are sent as a float instead of a string (default).

e.g. with this turned on, JSON serialization would output:

``````{
"value": 1.234
}
``````

#### `serde-str`

Note: it is recommended to use the `serde-with-*` features for greater control. This allows configurability at the data level.

This is typically useful for `bincode` or `csv` like implementations.

Since `bincode` does not specify type information, we need to ensure that a type hint is provided in order to correctly be able to deserialize. Enabling this feature on its own will force deserialization to use `deserialize_str` instead of `deserialize_any`.

If, for some reason, you also have `serde-float` enabled then this will use `deserialize_f64` as a type hint. Because converting to `f64` loses precision, it’s highly recommended that you do NOT enable this feature when working with `bincode`. That being said, this will only use 8 bytes so is slightly more efficient in terms of storage size.

#### `serde-arbitrary-precision`

Note: it is recommended to use the `serde-with-*` features for greater control. This allows configurability at the data level.

This is used primarily with `serde_json` and consequently adds it as a “weak dependency”. This supports the `arbitrary_precision` feature inside `serde_json` when parsing decimals.

This is recommended when parsing “float” looking data as it will prevent data loss.

#### `serde-with-float`

Enable this to access the module for serializing `Decimal` types to a float. This can be use in `struct` definitions like so:

``````#[derive(Serialize, Deserialize)]
pub struct FloatExample {
#[serde(with = "rust_decimal::serde::float")]
value: Decimal,
}``````
``````#[derive(Serialize, Deserialize)]
pub struct OptionFloatExample {
#[serde(with = "rust_decimal::serde::float_option")]
value: Option<Decimal>,
}``````

#### `serde-with-str`

Enable this to access the module for serializing `Decimal` types to a `String`. This can be use in `struct` definitions like so:

``````#[derive(Serialize, Deserialize)]
pub struct StrExample {
#[serde(with = "rust_decimal::serde::str")]
value: Decimal,
}``````
``````#[derive(Serialize, Deserialize)]
pub struct OptionStrExample {
#[serde(with = "rust_decimal::serde::str_option")]
value: Option<Decimal>,
}``````

#### `serde-with-arbitrary-precision`

Enable this to access the module for serializing `Decimal` types to a `String`. This can be use in `struct` definitions like so:

``````#[derive(Serialize, Deserialize)]
pub struct ArbitraryExample {
#[serde(with = "rust_decimal::serde::arbitrary_precision")]
value: Decimal,
}``````
``````#[derive(Serialize, Deserialize)]
pub struct OptionArbitraryExample {
#[serde(with = "rust_decimal::serde::arbitrary_precision_option")]
value: Option<Decimal>,
}``````

#### `std`

Enable `std` library support. This is enabled by default, however in the future will be opt in. For now, to support `no_std` libraries, this crate can be compiled with `--no-default-features`.

### Minimum Rust Compiler Version

The current minimum compiler version is `1.60.0` which was released on `2022-04-07`.

This library maintains support for rust compiler versions that are 4 minor versions away from the current stable rust compiler version. For example, if the current stable compiler version is `1.50.0` then we will guarantee support up to and including `1.46.0`. Of note, we will only update the minimum supported version if and when required.

## Modules

• A convenience module appropriate for glob imports (`use rust_decimal::prelude::*;`).
• Serde specific functionality to customize how a decimal is serialized/deserialized (`serde_with`)

## Structs

• `Decimal` represents a 128 bit representation of a fixed-precision decimal number. The finite set of values of type `Decimal` are of the form m / 10e, where m is an integer such that -296 < m < 296, and e is an integer between 0 and 28 inclusive.

## Enums

• Error type for the library.
• `RoundingStrategy` represents the different rounding strategies that can be used by `round_dp_with_strategy`.

## Traits

• Trait exposing various mathematical operations that can be applied using a Decimal. This is only present when the `maths` feature has been enabled.

## Type Definitions

• Shortcut for `core::result::Result<T, rust_decimal::Error>`. Useful to distinguish between `rust_decimal` and `std` types.