/**
 * Feistel index permutation — a "lottery with no tumbler".
 *
 * A keyed pseudo-random **bijection** on `[0, n)`: `permute(i, n, key)` maps
 * each row index to a unique, scrambled "slot" without ever building an
 * array. This is what lets the streaming engine place a sorted quota plan
 * (`[A×70%, B×30%]`) into random-looking positions and get EXACT percentages
 * — because a bijection sends exactly `0.7n` indices into the first `0.7n`
 * slots — with O(1) memory and O(1) per row.
 *
 * Construction: a balanced Feistel network on the smallest `2^(2·half) ≥ n`,
 * with **cycle-walking** to fold the domain back down to exactly `[0, n)` for
 * non-power-of-two `n` (re-apply until the result is in range; expected < 4
 * iterations since the padded domain is < 4n). `unpermute` is the inverse
 * (needed by uniq's mixed-radix decode later).
 *
 * Determinism is cross-language: the round function uses only `Math.imul` and
 * 32-bit ops, and the key comes from cyrb128. Combining halves uses plain
 * arithmetic (not bit-shifts) so it stays exact for `n` up to ~2^52.
 */
/** Derive a 32-bit round key for a permutation stream. */
export declare function permuteKey(seed: string, streamId: string): number;
/** Bijection `[0, n) → [0, n)`: the scrambled slot for row `index`. */
export declare function permute(index: number, n: number, key: number): number;
/** Inverse of `permute`: the row index that maps to `slot`. */
export declare function unpermute(slot: number, n: number, key: number): number;
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