Math

The Math Routines manipulate BCD and decimal numbers and store/transfer data.

Note: Most of the Math routines are undocumented in the Nutting Manual. Their definitions and usage are largely found in the system ROM source listing and Bally On-Board ROM Subroutines.

Math System Routines

Undocumented routines are marked with an asterisk (*)

Need documentation for most math routines

Name Description
BCDADD* BCD add
BCDCHS* BCD change sign
BCDDIV* BCD divide
BCDMUL* BCD multiply
BCDNEG* BCD negate
BCDSUB* BCD subtract
DABS* Decimal absolute value
DADD* Decimal add
DSMG* Decimal convert to sign magnitude
INDEXB Returns byte at address + displacement
INDEXN Look up a given nibble in a linear list
INDEXW Look up a given word in a linear list
MOVE Block transfer, copies bytes from source to destination
NEGT* Decimal negate
RANGED Generate ranged random number
SETB Store byte at a specified address
SETW Store 16-bit word at specified address
SHIFTU* Shift up digit in A
STOREN Store 4-bit nibble in a linear list

Math System Routine Descriptions

BCDADD

BCD ADDITION

Calling Sequence: 
SYSTEM    BCDADD

or 

SYSSUK    BCDADD
DW       (arg 1)
DB       (size/2 + 1)
DW       (arg 2)
Arguments: B = SIZE/2 + 1
DE = Argument 1
HL = Argument 2
Output: DE = Answer
Notes: None
Description:

BCDCHS

BCD CHANGE SIGN

Calling Sequence: 
SYSTEM    BCDCHS

or 

SYSSUK    BCDCHS
DB       ()
DW       ()
Arguments: B =
HL =
Output:
Notes: None
Description:

BCDDIV

BCD DIVISION

Calling Sequence: 
SYSTEM    BCDDIV

or 

SYSSUK    BCDDIV
DW       (arg 1)
DB       ()
DW       (arg 2)
Arguments: B =
DE =
HL = Argument 2
Output: ???
Notes: None
Description:

BCDMUL

BCD MULTIPLY

Calling Sequence: 
SYSTEM    BCDMUL

or 

SYSSUK    BCDMUL
DW       (arg 1)
DB       ()
DW       (arg 2)
Arguments: B =
DE =
HL =
Output: DE = Answer
Notes: None
Description:

BCDNEG

BCD NEGATE TO DECIMAL

Calling Sequence: 
SYSTEM    BCDNEG

or 

SYSSUK    BCDNEG
DW       ()
DB       ()
Arguments: B =
DE =
Output: ???
Notes: None
Description:

BCDSUB

BCD SUBTRACTION

Calling Sequence: 
SYSTEM    BCDSUB

or 

SYSSUK    BCDSUB
DW       (arg 1)
DB       ()
DW       (arg 2)
Arguments: B =
DE =
HL =
Output: DE = Answer
Notes: None
Description:

DABS

DECIMAL ABSOLUTE VALUE

Calling Sequence: 
SYSTEM    DABS

or 

SYSSUK    DABS
DW       ()
DB       ()
Arguments: B =
DE =
Output:
Notes: None
Description:

DADD

DECIMAL ADDITION

Calling Sequence: 
SYSTEM    DADD

or 

SYSSUK    DADD
DW       (arg 1)
DB       ()
DW       (arg 2)
Arguments: B =
DE =
HL =
Output: ???
Notes: None
Description:

DSMG

DECIMAL CONVERT TO SIGN MAGNITUDE

Calling Sequence: 
SYSTEM    DSMG

or 

SYSSUK    DSMG
DW       (arg 1)
DB       (size/2 + 1)
Arguments: B =
DE =
Output: ???
Notes: None
Description:

INDEXB

INDEX BYTE

Calling Sequence: 
SYSTEM    INDEXB

or 

SYSSUK    INDEX
DW       (base address)
Arguments: A = Displacement (0–255)
HL = Base address of table
Output: A = Entry looked up
HL = Address of entry looked up
Description: INDEXB returns the byte at address (Base address) + (Displacement)

INDEXN

INDEX NIBBLE

Calling Sequence: 
SYSTEM    INDEXN

or 

SYSSUK    INDEXN
DW       (base address)
Arguments: C = Nibble displacement (0–255)
HL = Base address of table
Output: A = Nibble value
Notes: Indexing illustration below
Description: INDEXN looks up a specified nibble in a linear list.

INDEXW

INDEX WORD

Calling Sequence: 
SYSTEM    INDEXW

or 

SYSSUK    INDEXW
DW       (base address)
Arguments: A = Displacement (0–255)
HL = Base address of table
Output: DE = Entry looked up
HL = Address of entry looked up
Notes: Indexing illustration below
Description: None

MOVE

MOVE BYTES

Calling Sequence: 
SYSTEM    MOVE

or 

SYSSUK    MOVE
DW       (destination)
DW       (number of bytes)
DW       (source)
Arguments: DE = Destination address
HL = Source address
BC = Number of bytes to transfer
Description: MOVE uses LDIR to copy bytes from source to destination.

NEGT

DECIMAL NEGATE

Calling Sequence: 
SYSTEM    NEGT

or 

SYSSUK    NEGT
DB       (B)
DW       (HL)
Arguments: B =
HL =
Output: ???
Notes: None
Description:

RANGED

RANGED RANDOM NUMBER

Calling Sequence: 
SYSTEM    RANGED

or 

SYSSUK    RANGED
DB       (N)
Arguments: A = Range
Output: A = Random Number (0 to Range - 1)
Notes: If N is a power of 2, it is considerably faster to use N=0, which causes an 8-bit value to be returned without ranging. Use an AND instruction to range it yourself.

RANGED uses a polynomial shift register RANSHT in system RAM. RANGED is called in GETNUM while waiting for game selection/parameter entry. Thus each execution of a program will receive different random numbers. For “predictable” random numbers, alter RANSHT yourself after parameter acceptance.
Description: Returns a ranged random number.

SETB

STORE BYTE

Calling Sequence: 
SYSTEM    SETB

or 

SYSSUK    SETB
DB       (value to store)
DW       (address)
Arguments: A = Byte value to store
HL = Storage address
Description: Stores an 8-bit value at a specified address.

SETW

STORE WORD

Calling Sequence: 
SYSTEM    SETW

or 

SYSSUK    SETW
DW       (value to store)
DW       (address)
Arguments: DE = Word value to store
HL = Storage address
Description: Stores a 16-bit value at a specified address.

SHIFTU

SHIFT UP DIGIT IN A

Calling Sequence: 
SYSTEM    ????
Arguments:
Notes:
Description: Shift up digit in A

STOREN

STORE NIBBLE

Calling Sequence: 
SYSTEM    STOREN

or 

SYSSUK    STOREN
DW       (base address)
Arguments: C = Nibble displacement (not loaded)
HL = Base address
A = Nibble value to store (not loaded)
Description: STOREN is the inverse of INDEXN but functions identically.