uint128

uint128 is an extended-precision unsigned integer — a fixed-width type whose size is identical on every target platform. It stores non-negative values in plain binary and wraps modulo 2¹²⁸ on overflow. No mainstream CPU has native 128-bit arithmetic, so operations are lowered to pairs of 64-bit instructions and run several times slower than native types — reserve uint128 for code that genuinely needs the extra range.

Literals

let a: uint128 = 340282366920938463463374607431768211455;
let b = 42u128;  // type suffix

If a literal value does not fit in uint128, the compiler emits an error at compile time. See Literals for decimal, hexadecimal, octal, and binary forms.

Typical Use Cases

• IPv6 addresses
• GUIDs / UUIDs
• 128-bit hash values

Arithmetic

let a: uint128 = 10;
let b: uint128 = 3;

let sum  = a + b;   // 13
let quot = a / b;   // 3   truncates toward zero
let rem  = a % b;   // 1   always non-negative

Division truncates toward zero. Because unsigned values are never negative, both the quotient and the remainder are always non-negative.

Overflow. Unsigned arithmetic wraps modulo 2¹²⁸ in both debug and release builds — it never triggers a fatal error. Subtracting past zero wraps to a large value rather than going negative (0 - 1 yields 2¹²⁸−1), so prefer a signed type for any value that can legitimately fall below zero.

Comparison

Both operands must have the same type. Comparing uint128 with another integer type — or with a signed type such as int128 — is a compile-time error; cast one operand explicitly first.

Shift and Bitwise

Right shift on an unsigned value is logical: the vacated high bits are filled with zeros, never a sign bit. Left shift likewise fills the vacated low bits with zeros.

let u: uint128 = 20;  // 0b00010100
let l = u << 2;       // 80   logical left shift
let r = u >> 2;       //  5   logical right shift, zero-filled

Unsigned types are the natural home for bit manipulation; the operators & (AND), | (OR), ^ (XOR), and ~ (NOT) are all defined.

let a: uint128 = 0b1100;  // 12
let b: uint128 = 0b1010;  // 10
let and = a & b;          // 0b1000 = 8
let or  = a | b;          // 0b1110 = 14
let xor = a ^ b;          // 0b0110 = 6

Conversion

Rux performs no implicit numeric conversions — every conversion uses the as operator. Widening zero-extends, preserving the value; narrowing keeps only the low-order bits; a same-width unsigned↔signed cast reinterprets the bit pattern.

let x: uint128 = 1;
let wide  = x as uint256;  // 1   zero-extended, value preserved
let small = x as uint64;   // 1   narrowed, low 64 bits kept
let s     = x as int128;   // 1   same width, bits reinterpreted

See Also

• int128 — signed counterpart of the same width
• Signed Integer Types — the signed integer family