## Expand description

## §Arbitrary-precision numbers

Rug provides integers and floating-point numbers with arbitrary precision and correct rounding:

`Integer`

is a bignum integer with arbitrary precision,`Rational`

is a bignum rational number with arbitrary precision,`Float`

is a multi-precision floating-point number with correct rounding, and`Complex`

is a multi-precision complex number with correct rounding.

Rug is a high-level interface to the following GNU libraries:

- GMP for integers and rational numbers,
- MPFR for floating-point numbers, and
- MPC for complex numbers.

Rug is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. See the full text of the GNU LGPL and GNU GPL for details.

You are also free to use the examples in this documentation without any restrictions; the examples are in the public domain.

### §Quick example

```
use rug::{Assign, Integer};
let mut int = Integer::new();
assert_eq!(int, 0);
int.assign(14);
assert_eq!(int, 14);
let decimal = "98_765_432_109_876_543_210";
int.assign(Integer::parse(decimal).unwrap());
assert!(int > 100_000_000);
let hex_160 = "ffff0000ffff0000ffff0000ffff0000ffff0000";
int.assign(Integer::parse_radix(hex_160, 16).unwrap());
assert_eq!(int.significant_bits(), 160);
int = (int >> 128) - 1;
assert_eq!(int, 0xfffe_ffff_u32);
```

`Integer::new`

creates a new`Integer`

intialized to zero.- To assign values to Rug types, we use the
`Assign`

trait and its method`Assign::assign`

. We do not use the assignment operator`=`

as that would drop the left-hand-side operand and replace it with a right-hand-side operand of the same type, which is not what we want here. - Arbitrary precision numbers can hold numbers that are too large to fit in a
primitive type. To assign such a number to the large types, we use strings
rather than primitives; in the example this is done using
`Integer::parse`

and`Integer::parse_radix`

. - We can compare Rug types to primitive types or to other Rug types using the
normal comparison operators, for example
`int > 100_000_000`

. - Most arithmetic operations are supported with Rug types and primitive types
on either side of the operator, for example
`int >> 128`

.

### §Using with primitive types

With Rust primitive types, arithmetic operators usually operate on two values of
the same type, for example `12i32 + 5i32`

. Unlike primitive types, conversion to
and from Rug types can be expensive, so the arithmetic operators are overloaded
to work on many combinations of Rug types and primitives. The following are
provided:

- Where they make sense, all arithmetic operators are overloaded to work with
Rug types and the primitives
`i8`

,`i16`

,`i32`

,`i64`

,`i128`

,`u8`

,`u16`

,`u32`

,`u64`

,`u128`

,`f32`

and`f64`

. - Where they make sense, conversions using the
`From`

trait and assignments using the`Assign`

trait are supported for all the primitives in 1 above as well as`bool`

,`isize`

and`usize`

. - Comparisons between Rug types and all the numeric primitives listed in 1 and 2 above are supported.
- For
`Rational`

numbers, conversions and comparisons are also supported for tuples containing two integer primitives: the first is the numerator and the second is the denominator which must not be zero. The two primitives do not need to be of the same type. - For
`Complex`

numbers, conversions and comparisons are also supported for tuples containing two primitives: the first is the real part and the second is the imaginary part. The two primitives do not need to be of the same type.

### §Operators

Operators are overloaded to work on Rug types alone or on a combination of Rug types and Rust primitives. When at least one operand is an owned value of a Rug type, the operation will consume that value and return a value of the Rug type. For example

```
use rug::Integer;
let a = Integer::from(10);
let b = 5 - a;
assert_eq!(b, 5 - 10);
```

Here `a`

is consumed by the subtraction, and `b`

is an owned `Integer`

.

If on the other hand there are no owned Rug types and there are references instead, the returned value is not the final value, but an incomplete-computation value. For example

```
use rug::Integer;
let (a, b) = (Integer::from(10), Integer::from(20));
let incomplete = &a - &b;
// This would fail to compile: assert_eq!(incomplete, -10);
let sub = Integer::from(incomplete);
assert_eq!(sub, -10);
```

Here `a`

and `b`

are not consumed, and `incomplete`

is not the final value. It
still needs to be converted or assigned into an `Integer`

. This is covered in
more detail in the *Incomplete-computation values* section.

#### §Shifting operations

The left shift `<<`

and right shift `>>`

operators support shifting by negative
values, for example `a << 5`

is equivalent to `a >> -5`

.

The shifting operators are also supported for the `Float`

and `Complex`

number types, where they are equivalent to multiplication or division by a power
of two. Only the exponent of the value is affected; the mantissa is unchanged.

#### §Exponentiation

Exponentiation (raising to a power) does not have a dedicated operator in Rust.
In order to perform exponentiation of Rug types, the `Pow`

trait has
to be brought into scope, for example

```
use rug::ops::Pow;
use rug::Integer;
let base = Integer::from(10);
let power = base.pow(5);
assert_eq!(power, 100_000);
```

#### §Compound assignments to right-hand-side operands

Traits are provided for compound assignment to right-hand-side operands. This
can be useful for non-commutative operations like subtraction. The names of the
traits and their methods are similar to Rust compound assignment traits, with
the suffix “`Assign`

” replaced with “`From`

”. For example the counterpart to
`SubAssign`

is `SubFrom`

:

```
use rug::ops::SubFrom;
use rug::Integer;
let mut rhs = Integer::from(10);
// set rhs = 100 - rhs
rhs.sub_from(100);
assert_eq!(rhs, 90);
```

### §Incomplete-computation values

There are two main reasons why operations like `&a - &b`

do not perform a
complete computation and return a Rug type:

- Sometimes we need to assign the result to an object that already exists. Since Rug types require memory allocations, this can help reduce the number of allocations. (While the allocations might not affect performance noticeably for computationally intensive functions, they can have a much more significant effect on faster functions like addition.)
- For the
`Float`

and`Complex`

number types, we need to know the precision when we create a value, and the operation itself does not convey information about what precision is desired for the result.

There are two things that can be done with incomplete-computation values:

- Assign them to an existing object without unnecessary allocations. This is
usually achieved using the
`Assign`

trait or a similar method, for example`int.assign(incomplete)`

and`float.assign_round(incomplete, Round::Up)`

. - Convert them to the final value using the
`Complete`

trait, the`From`

trait or a similar method. For example incomplete integers can be completed using`incomplete.complete()`

or`Integer::from(incomplete)`

. Incomplete floating-point numbers can be completed using`incomplete.complete(53)`

or`Float::with_val(53, incomplete)`

since the precision has to be specified.

Let us consider a couple of examples.

```
use rug::{Assign, Integer};
let mut buffer = Integer::new();
// ... buffer can be used and reused ...
let (a, b) = (Integer::from(10), Integer::from(20));
let incomplete = &a - &b;
buffer.assign(incomplete);
assert_eq!(buffer, -10);
```

Here the assignment from `incomplete`

into `buffer`

does not require an
allocation unless the result does not fit in the current capacity of `buffer`

.
If `&a - &b`

returned an `Integer`

instead, then an allocation would take
place even if it is not necessary.

```
use rug::float::Constant;
use rug::Float;
// x has a precision of 10 bits
let x = Float::with_val(10, 180);
// y has a precision of 50 bits
let y = Float::with_val(50, Constant::Pi);
let incomplete = &x / &y;
// z has a precision of 45 bits
let z = Float::with_val(45, incomplete);
assert!(57.295 < z && z < 57.296);
```

The precision to use for the result depends on the requirements of the algorithm
being implemented. Here `z`

is created with a precision of 45.

Many operations can return incomplete-computation values, for example

- unary operators applied to references, for example
`-&int`

- binary operators applied to two references, for example
`&int1 + &int2`

- binary operators applied to a primitive and a reference, for example
`&int * 10`

- methods that take a reference, for example
`int.abs_ref()`

- methods that take two references, for example
`int1.gcd_ref(&int2)`

- string parsing, for example
`Integer::parse("12")`

These operations return objects that can be stored in temporary variables like
`incomplete`

in the last few code examples. However, the names of the types are
not public, and consequently, the incomplete-computation values cannot be for
example stored in a struct. If you need to store the value in a struct, complete
it to its final type and value.

### §Using Rug

Rug is available on crates.io. To use Rug in your crate, add it as
a dependency inside *Cargo.toml*:

```
[dependencies]
rug = "1.25"
```

Rug requires rustc version 1.65.0 or later.

Rug also depends on the GMP, MPFR and MPC libraries through the low-level FFI bindings in the gmp-mpfr-sys crate, which needs some setup to build; the gmp-mpfr-sys documentation has some details on usage under GNU/Linux, macOS and Windows.

### §Optional features

The Rug crate has six optional features:

`integer`

, enabled by default. Required for the`Integer`

type and its supporting features.`rational`

, enabled by default. Required for the`Rational`

number type and its supporting features. This feature requires the`integer`

feature.`float`

, enabled by default. Required for the`Float`

type and its supporting features.`complex`

, enabled by default. Required for the`Complex`

number type and its supporting features. This feature requires the`float`

feature.`rand`

, enabled by default. Required for the`RandState`

type and its supporting features. This feature requires the`integer`

feature.`std`

, enabled by default. This is for features that are not possible under`no_std`

, such as methods that return`String`

or the implementation of the`Error`

trait.`serde`

, disabled by default. This provides serialization support for the`Integer`

,`Rational`

,`Float`

and`Complex`

number types, providing that they are enabled. This feature requires the`std`

feature and the serde crate.

The first six optional features are enabled by default; to use features
selectively, you can add the dependency like this to *Cargo.toml*:

```
[dependencies.rug]
version = "1.25"
default-features = false
features = ["integer", "float", "std"]
```

Here only the `integer`

, `float`

and `rand`

features are enabled. If none of the
features are selected, the gmp-mpfr-sys crate is not required and
thus not enabled. In that case, only the `Assign`

trait and the traits that
are in the `ops`

module are provided by the crate.

### §Experimental optional features

It is not considered a breaking change if the following experimental features are removed. The removal of experimental features would however require a minor version bump. Similarly, on a minor version bump, optional dependencies can be updated to an incompatible newer version.

`num-traits`

, disabled by default. This implements some traits from the*num-traits*crate and the*num-integer*crate. (The plan is to promote this to an optional feature once the*num-traits*crate and the*num-integer*crate reach version 1.0.0.)

## Modules§

- Multi-precision complex numbers with correct rounding.
- Multi-precision floating-point numbers with correct rounding.
- Arbitrary-precision integers.
- Operations on numbers.
- Random number generation.
- Arbitrary-precision rational numbers.

## Structs§

- A multi-precision complex number with arbitrarily large precision and correct rounding.
- A multi-precision floating-point number with arbitrarily large precision and correct rounding
- An arbitrary-precision integer.
- An arbitrary-precision rational number.

## Traits§

- Assigns to a number from another value.
- Completes an incomplete-computation value.