# Crate rust_decimal[−][src]

Expand description

A Decimal 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.

## Getting started

To get started, add `rust_decimal` and optionally `rust_decimal_macros` to your `Cargo.toml`:

``````[dependencies]
rust_decimal = "1.14"
rust_decimal_macros = "1.14"
``````

## Usage

Decimal numbers can be created in a few distinct ways. The easiest and most optimal 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);
assert_eq!("-1.23", number.to_string());```

Alternatively you can also use one of the Decimal number convenience functions:

```// 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 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
let from_string_base16 = Decimal::from_str_radix("ffff", 16).unwrap();
assert_eq!("65535", from_string_base16.to_string());

// Using the `Into` trait
let my_int: Decimal = 3i32.into();
assert_eq!("3", my_int.to_string());

// Using the raw decimal representation
let pi = Decimal::from_parts(1102470952, 185874565, 1703060790, 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::*;

let amount = Decimal::from_str("25.12").unwrap();
let tax = Decimal::from_str("0.085").unwrap();
let total = amount + (amount * tax).round_dp(2);
assert_eq!(total.to_string(), "27.26");```

## `c-repr`

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

## `db-postgres`

This feature 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.

## `legacy-ops`

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.

## `rust-fuzz`

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

## `serde-float`

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`

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`

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.

## `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`.

## Modules

 prelude A convenience module appropriate for glob imports (`use rust_decimal::prelude::*;`).

## Structs

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

## Traits

 MathematicalOps 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

 Result Shortcut for `core::result::Result`. Useful to distinguish between `rust_decimal` and `std` types.