float80

float80 is an extended-precision float matching the Intel x87 80-bit format — not a standard IEEE 754 binary format, though it shares the same structure and rounding rules. It provides extra guard bits during intermediate calculations. Special values (Inf, -Inf, NaN) are supported, and division by zero produces Inf or NaN rather than a fatal error. On targets without an x87 FPU it falls back to float128.

Literals

let precise: float80 = 1.234567890123456789;  // explicit annotation
let v = 1.0f80;                               // type suffix

Unsuffixed floating-point literals default to float64; request float80 with the f80 suffix or an annotation. Decimal and scientific forms (1.5e10) are both accepted — see Literals.

Typical Use Cases

• Guard bits during intermediate calculations
• Interop with legacy x87 code

Arithmetic

let a: float80 = 10.0;
let b: float80 = 3.0;

let sum  = a + b;   // 13.0
let quot = a / b;   // 3.333…
let rem  = a % b;   // 1.0

Both operands must share the same type; mixed-width expressions require an explicit cast. Arithmetic rounds to nearest (ties to even), unary negation (-x) flips the sign, and results that exceed the range overflow to Inf. Subtracting nearly equal values loses significant digits (catastrophic cancellation) — reorder the computation or use a wider type when accuracy matters.

Division by zero never fails: it yields signed infinity, and 0.0 / 0.0 yields NaN. Inf and NaN then propagate — Inf - Inf and Inf * 0.0 are both NaN.

let p =  1.0 / 0.0;  //  Inf
let n = -1.0 / 0.0;  // -Inf
let u =  0.0 / 0.0;  //  NaN

Comparison

Both operands must have the same type; comparing a different float width, or a float with an integer, is a compile-time error — cast explicitly first.

NaN is unordered: every comparison involving it returns false, including NaN == NaN. Detect it with IsNan, never ==. For the same reason, avoid == between computed results and compare within a tolerance instead:

let x = 0.1 + 0.2;
let close = Abs(x - 0.3) < 1.0e-15;  // not  x == 0.3

Conversion

Rux implicitly widens to any larger float type, so no precision is lost. Narrowing must be explicit and rounds to nearest (ties to even).

let x: float80 = 1.5;
let wide: float128 = x;      // widening — implicit
let narrow = x as float64;   // narrowing — explicit cast

Float-to-integer conversions are always explicit and truncate toward zero; casting NaN or Inf to an integer raises a fatal error in debug builds.

let whole = x as int32;      // 1   truncates toward zero

See Also

• float64 — the default double-precision float
• float128 — the fallback type on non-x87 targets