DeFiMath v3.1.0 released - cbrt function

A focused minor release adding cbrt — the missing primitive for cube roots in 18-decimal fixed-point — implemented with the same CLZ + Newton-Raphson recipe that powers sqrt.

New: cbrt

• 368 gas average on a 1e-4 → 1e4 sweep
• ~33% cheaper than Solady's cbrtWad (550 gas) at identical precision (both bit-exact at the ulp limit, max rel error 2.2e-14%)
• 6 Newton iterations from a CLZ-derived initial guess (y₀ = 2^⌈bits/3⌉), within factor ∛2 of the true root
• Domain: 0 ≤ x < 2⁷⁶ ≈ 7.6e22 in 18-decimal fixed-point; reverts with CbrtUpperBoundError above that
• Single-branch implementation: result = integer_cbrt(x · 1e36) works symmetrically across the full domain, no inversion trick needed

import "defimath-lib/contracts/math/Math.sol";

uint256 root = DeFiMath.cbrt(8e18); // 2e18

Like the rest of DeFiMath, cbrt is internal pure, no storage access, no external calls.

Why it matters

Cube roots show up in higher-order risk math (skew, kurtosis adjustments), Cardano's formula for cubic equations, and a handful of volatility models. Until now the only on-chain option was Solady's cbrtWad; DeFiMath gives the same primitive at a third less gas with no precision trade-off.

DeFiMath at v3.1.0 continues the pattern: every primitive measured against existing on-chain implementations, every branch covered by tests.