src/types/numeric.md

# Numeric types

## Integer types

The unsigned integer types consist of:

Type   | Minimum | Maximum
-------|---------|-------------------
`u8`   | 0       | 2<sup>8</sup>-1
`u16`  | 0       | 2<sup>16</sup>-1
`u32`  | 0       | 2<sup>32</sup>-1
`u64`  | 0       | 2<sup>64</sup>-1
`u128` | 0       | 2<sup>128</sup>-1

The signed two's complement integer types consist of:

Type   | Minimum            | Maximum
-------|--------------------|-------------------
`i8`   | -(2<sup>7</sup>)   | 2<sup>7</sup>-1
`i16`  | -(2<sup>15</sup>)  | 2<sup>15</sup>-1
`i32`  | -(2<sup>31</sup>)  | 2<sup>31</sup>-1
`i64`  | -(2<sup>63</sup>)  | 2<sup>63</sup>-1
`i128` | -(2<sup>127</sup>) | 2<sup>127</sup>-1


## Floating-point types

The IEEE 754-2008 "binary32" and "binary64" floating-point types are `f32` and
`f64`, respectively.

## Machine-dependent integer types

The `usize` type is an unsigned integer type with the same number of bits as the
platform's pointer type. It can represent every memory address in the process.

The `isize` type is a signed integer type with the same number of bits as the
platform's pointer type. The theoretical upper bound on object and array size
is the maximum `isize` value. This ensures that `isize` can be used to calculate
differences between pointers into an object or array and can address every byte
within an object along with one byte past the end.

`usize` and `isize` are at least 16-bits wide.

> **Note**: Many pieces of Rust code may assume that pointers, `usize`, and
> `isize` are either 32-bit or 64-bit. As a consequence, 16-bit
> pointer support is limited and may require explicit care and acknowledgment
> from a library to support.

## Bit validity

For every numeric type, `T`, the bit validity of `T` is equivalent to the bit
validity of `[u8; size_of::<T>()]`. An uninitialized byte is not a valid `u8`.