rot13 state

Rot13

Rot13 applies the ROT13 substitution cipher, rotating ASCII letters by 13 and leaving every other byte untouched. Because 13 is half of 26, Rot13(Rot13(s)) == s — the cipher is its own inverse. This mirrors the canonical strings.Map example from the Go docs.

rot13Rune

rot13Rune is the mapping function handed to strings.Map — the heart of the classic example.

Caesar

Caesar generalizes ROT13 to an arbitrary shift. Negative and large shifts are normalized into \[0,26). Only ASCII letters move; anything else passes through unchanged. Caesar(s, 13) is exactly Rot13(s).

hexNibble

hexNibble decodes a single hex digit, returning -1 if invalid.

percentDecode

percentDecode turns "%20"/"+" style path escapes back into readable text so gnoweb links with spaces or punctuation round-trip nicely. Invalid escapes are left verbatim.

Render

Render is the gnoweb entry point (not a crossing call). Render("") -> explanation + a worked example Render("/Hello, Gno!") -> the input and its ROT13 Render("/caesar/3/attack") -> a Caesar shift of 3 applied to "attack"

renderRoot

renderRot13

renderCaesar