decimal

Exact, arbitrary-precision fixed-point decimal for Go. A value is coefficient × 10⁻ˢᶜᵃˡᵉ with a big.Int coefficient — no precision ceiling, no float, immutable.

Unlike int64/uint64 decimal & money libraries (which cap around 19 digits — about $9.20 at 18 decimals), this holds a fiat cent and an 18-decimal on-chain wei balance with equal exactness. 0.1 + 0.2 is exactly 0.3.

d := decimal.MustParse("6.60")
cost := decimal.New(200, 0).Mul(d).Quo(decimal.New(1_000_000, 0), 18) // 200 tokens @ $6.60/1M
cost.String() // "0.00132"  (never floored to 0)

The numeric core beneath hanzoai/money. Stdlib only. MIT.