;password generation procedure for Casino Games (Sega Master System)
;contact : tigrou dot ind at gmail dot com

;account name start at C90E, and is encoded in ascii (A = 0x41, Z = 0x5A, ...) (10 bytes)
;money start at C927, and is encoded in BCD (eg: 10 20 95 00 for $00952010) (4 bytes)
;generated account number start at C91B, first encoded as unpacked BCD (eg : 04 02 03 04 08 09 00 01 05 09) (10 bytes)
;the account is then converted to ascii for display (eg : 34 32 33 34 38 39 30 31 35 39)

;account[7] = rand(0, 9)					
;account[8] = money[0]
;account[2] = money[1]
;account[4] = money[2]
;account[1] = money[3]
;account[6] = money[4]
;account[9] = money[5]
;account[0] = money[6]
;account[5] = name_checksum
;account[3] = final_checkum

;name_checksum = (sum(name) + rand) % 256 % 10		
;final_checkum = (circular_left_shift(account) + sum(account)) % 256 % 10

;main routine

00004ED3:	LD A,0Ah
00004ED5:	CALL 11CBh    ;generate a random number between 0-9 
00004ED8:	LD (C922h),A  ;random number => account 08

00004EDB:	LD HL,C92Ah
00004EDE:	CALL 4F27h    
00004EE1:	LD (C923h),A  ;money 1st digit => account 09
00004EE4:	CALL 4F2Eh    
00004EE7:	LD (C91Dh),A  ;money 2nd digit => account 03

00004EEA:	DEC HL      
00004EEB:	CALL 4F27h
00004EEE:	LD (C91Fh),A  ;money 3rd digit => account 05
00004EF1:	CALL 4F2Eh
00004EF4:	LD (C91Ch),A  ;money 4th digit => account 02

00004EF7:	DEC HL      
00004EF8:	CALL 4F27h
00004EFB:	LD (C921h),A  ;money 5th digit => account 07
00004EFE:	CALL 4F2Eh
00004F01:	LD (C924h),A  ;money 6th digit => account 10

00004F04:	DEC HL      
00004F05:	CALL 4F27h
00004F08:	LD (C91Bh),A  ;money 7th digit => account 01

00004F0B:	CALL 4F3Dh    ;compute crc on name
00004F0E:	CALL 4F31h    ;add random value generated previously
00004F11:	LD (C920h),A  ;crc name => account 06

00004F14:	CALL 4F4Dh    ;compute crc on all previously generated account digits (except 4th digit)
00004F17:	LD (C91Eh),A  ;crc account => account 04

00004F1A:	LD HL,C91Bh   ;convert all generated digits to ascii
00004F1D:	LD B,0Ah
00004F1F:	LD A,(HL)
00004F20:	ADD 30h       ;+ 0x30
00004F22:	LD (HL),A
00004F23:	INC HL
00004F24:	DJNZ -07h
00004F26:	RET


;extract nibble, add random digit (0-9), then modulo 10

00004F27:	LD A,(HL)     
00004F28:	RRCA          ;swap nibbles (eg : 0x25 => 0x52)
00004F29:	RRCA          ;
00004F2A:	RRCA          ;
00004F2B:	RRCA          ;
00004F2C:	JR +01h

00004F2E:	LD A,(HL)
00004F2F:	AND 0Fh       ;extract nibble  (eg : 0x52 => 0x02)

00004F31:	LD C,A
00004F32:	LD A,(C922h)  ;add randomizer (0-9)
00004F35:	ADD C         ;
00004F36:	SUB 0Ah       ;modulo 10
00004F38:	JR NC,-04h    ;
00004F3A:	ADD 0Ah       ; 
00004F3C:	RET

;crc for name and account number
 
00004F3D:	XOR A         ;compute name crc
00004F3E:	LD HL,C90Eh  
00004F41:	LD B,0Ah
00004F43:	CALL 4F48h    ;sum each character
00004F46:	JR -12h       

00004F48:	ADD (HL)      ;crc summing subroutine
00004F49:	INC HL
00004F4A:	DJNZ -04h
00004F4C:	RET


00004F4D:	XOR A         ;compute account crc
00004F4E:	LD HL,C91Bh
00004F51:	LD B,03h
00004F53:	CALL 4F6Ch    ;xor crc for digits 1-3

00004F56:	INC HL        ;4th digit is skipped
00004F57:	LD B,06h
00004F59:	CALL 4F6Ch    ;xor crc for digits 5-10

00004F5C:	LD HL,C91Bh  
00004F5F:	LD B,03h      
00004F61:	CALL 4F48h    ;sum crc for digits 1-3

00004F64:	INC HL        ;4th digit is skipped
00004F65:	LD B,06h      
00004F67:	CALL 4F48h    ;sum crc for digits 5-10
00004F6A:	JR -36h

00004F6C:	RLCA          ;crc left circular shift + xor subroutine
00004F6D:	XOR (HL)
00004F6E:	INC HL
00004F6F:	DJNZ -05h
00004F71:	RET