The uint! macro for Uint and Bits literals

Within the uint! macro arguments, you can write Uint and Bits literals using the same syntax as Rust integer literals, but using a capital U or B suffix respectively. Note that there is ambiguity for hexadecimals with a B suffix, to lessen the impact an underscore is required in this case.

To use it simply import it in scope:

use ruint::uint;

Now constants can be created in decimal, hex, binary and even octal:

# use ruint::uint;
let avogadro = uint!(602_214_076_000_000_000_000_000_U256);
let cow_key = uint!(0xee79b5f6e221356af78cf4c36f4f7885a11b67dfcc81c34d80249947330c0f82_U256);
let bender = uint!(0b1010011010_U10);

The uint! macro recurses through the parse tree, so the above can equivalently be written

# use ruint::uint;
uint! {
let avogadro = 602_214_076_000_000_000_000_000_U256;
let cow_key = 0xee79b5f6e221356af78cf4c36f4f7885a11b67dfcc81c34d80249947330c0f82_U256;
let bender = 0b1010011010_U10;
}

This latter form is particularly useful for lookup tables:

# use ruint::{Uint, uint};
const PRIMES: [Uint<128, 2>; 3] = uint!([
    170141183460469231731687303715884105757_U128,
    170141183460469231731687303715884105773_U128,
    170141183460469231731687303715884105793_U128,
]);

The macro will throw a compile time error if you try to create a constant that does not fit the type:

# use ruint::uint;
# uint! {
let sparta = 300_U8;
# }

error: Value too large for Uint<8>: 300
 --> src/example.rs:1:14
  |
1 | let sparta = 300_U8;
  |              ^^^^^^

References

• Rust integer literals syntax.