Downhill

; llama_case_flip: strictly descending gate. The old version was a second
; XOR-0x20 case flip, a duplicate of the intro XOR puzzle. This is a structural
; check instead: it walks the input and demands each byte be strictly LESS than
; the one before it, so the whole word marches downhill. No key to recover; the
; player reads the RULE off the loop (cmp cur, prev / jge fail). Technique:
; descending order gate. r0 = 1 on accept. Accept rule: nonzero.
;
; sample "SPED": S > P > E > D as unsigned bytes.

        len   r2
        cmp   r2, 4
        jnz   bad           ; exactly 4 bytes

        mov   r7, 0
        ldb   r3, [r7]      ; prev = s[0]
        mov   r7, 1
next:   cmp   r7, r2
        jge   ok            ; scanned every byte -> accept
        ldb   r0, [r7]      ; cur = s[r7]
        cmp   r0, r3
        jge   bad           ; cur >= prev -> not strictly descending
        mov   r3, r0        ; prev = cur
        inc   r7
        jmp   next
ok:     mov   r0, 1
        ret
bad:    mov   r0, 0
        ret