( Low-level part of ROLL. Example:
"1 2 3 4 4 (roll)" --> "1 3 4 4". No sanity checks, never
call with 0. )
CODE (roll)
HL POP,
B H LDrr,
C L LDrr,
SP ADDHLd,
HL INCd,
D H LDrr,
E L LDrr,
HL DECd,
LDDR,
;CODE