Function det_exp 

pub fn det_exp(x: f64) -> f64

Deterministic exp(x) — classical exp polynomial with Cody-Waite ln(2) range reduction.

Strategy: argument-reduce to x = k·ln(2) + r with |r| ≤ 0.5·ln(2), evaluate exp(r) via a 5-term polynomial in r², then scale by 2^k using direct exponent-bit manipulation. All operations are pure IEEE 754 arithmetic + bit cast — bit-exact across iOS / Android / x86_64 / WASM.