Dynamite Dan: Routine at FFDE

FFDE: Decrypt a data block using bit twiddling

Used by the routine at FF70.

Input
HL	Start address
BC	Length
D	Initial salt

FFDE

LD A,D

Get salt

FFDF

XOR (HL)

Flip bits on the next byte against it

FFE0

LD (HL),A

Store new value

FFE1

INC HL

Point to next byte

FFE2

DEC BC

Decrease length

FFE3

LD A,B

Is length 0?

FFE4

OR C

FFE5

JR NZ,$FFDE

No, loop back for more

FFE7

RET

All done