pub fn alpha_suffix(n: usize) -> StringExpand description
Infinite alphabetic suffix sequence. n=0 yields the first suffix
past Decillion. The sequence is grouped into phases; phase L≥0
produces all (L+2)-letter strings, first all-lowercase, then
capital-first. Each phase has 2 × 26^(L+2) entries.
Concretely:
n = 0..676 → aa, ab, …, az, ba, …, zz (676 = 26² lowercase pairs)
n = 676..1352 → Aa, Ab, …, Az, Ba, …, Zz (676 uppercase-first pairs)
n = 1352..1352+17576 → aaa, aab, …, zzz (17576 = 26³ lowercase triples)
n = … + 17576 → Aaa, Aab, …, Zzz (uppercase-first triples)
…Each suffix step represents three more orders of magnitude on top of
10^33 ≈ Dc, so phase 0 alone covers 10^36 … 10^(33 + 676·3) =
10^36 … 10^2061 — already past f64::MAX ≈ 1.8e308. The higher
phases exist so the helper remains correct under any future
arbitrary-precision number type.