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Math
The Math Routines manipulate floating BCD and decimal numbers, transfer data, and halt cartridge execution.
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 (*)
| 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 |
| QUIT* | Quit cartridge execution |
| 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 () DW () DB () |
| Arguments: | B = SIZE/2 + 1 DE = Argument 1 HL = Argument 2 |
| Output: | DE = Answer |
| Notes: | None |
| Description: |
BCDCHS
BCD CHANGE SIGN
BCDDIV
BCD DIVISION
BCDMUL
BCD MULTIPLY
BCDNEG
BCD NEGATE TO DECIMAL
BCDSUB
BCD SUBTRACTION
DABS
DECIMAL ABSOLUTE VALUE
DADD
DECIMAL ADDITION
DSMG
DECIMAL CONVERT TO SIGN MAGNITUDE
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 |
| Notes: | None |
| Description: | INDEXB returns the byte at address (Base address) + (Displacement) |
| Restrictions: | None |
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. |
| Restrictions: | None |
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 |
| Notes: | None |
| Description: | MOVE uses LDIR to copy bytes from source to destination. |
| Restrictions: | None |
NEGT
DECIMAL NEGATE
QUIT
QUIT CARTRIDGE EXECUTION
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. |
| Restrictions: | None |
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 |
| Notes: | None |
| Description: | Stores an 8-bit value at a specified address. |
| Restrictions: | None |
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 |
| Notes: | None |
| Description: | Stores a 16-bit value at a specified address. |
| Restrictions: | None |
SHIFTU
SHIFT UP DIGIT IN A
| Calling Sequence: | SYSTEM ????
|
| Arguments: | |
| Notes: | Currently undocumented |
| Description: | Shift up digit in A |
| Restrictions: | None |
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) |
| Notes: | None |
| Description: | STOREN is the inverse of INDEXN but functions identically. |
| Restrictions: | None |
