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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 operating system source listing and [[http://www.ballyalley.com/basic/bally_on-board_rom_subroutines.pdf|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 |
-| [[math routines#indexb|INDEXB]] | Returns byte at address + displacement |
-| [[math routines#indexn|INDEXN]] | Look up a given nibble in a linear list |
-| [[math routines#indexw|INDEXW]] | Look up a given word in a linear list |
-| [[math routines#move|MOVE]] | Block transfer, copies bytes from source to destination |
-| NEGT* | Decimal negate |
-| QUIT* | Quit cartridge execution (holds present game score until key hit or game over) |
-| [[math routines#ranged|RANGED]] | Generate ranged random number |
-| [[math routines#setb|SETB]] | Store byte at a specified address |
-| [[math routines#setw|SETW]] | Store 16-bit word at specified address |
-| SHIFTU* | Shift up digit in A |
-| [[math routines#storen|STOREN]] | Store 4-bit nibble  in a linear list |
-===== Math System Routine Descriptions =====
-==== BCDADD ====
-BCD ADDITION
-| Calling Sequence: | <code z80>SYSTEM    BCDADD</code> or <code z80>SYSSUK    BCDADD
-DW       ()
-DW       ()
-DB       ()</code>|
-| 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 ====
-==== DABS ====
-==== DADD ====
-DECIMAL ADDITION
-==== DSMG ====
-DECIMAL CONVERT TO SIGN MAGNITUDE
-==== INDEXB ====
-INDEX BYTE
-| Calling Sequence: | <code z80>SYSTEM    INDEXB</code> or <code z80>SYSSUK    INDEX
-DW       (base address)</code>|
-| 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: | <code z80>SYSTEM    INDEXN</code> or <code z80>SYSSUK    INDEXN
-DW       (base address)</code>|
-| 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 |
-{{indexn.png}}
-==== INDEXW ====
-INDEX WORD
-| Calling Sequence: | <code z80>SYSTEM    INDEXW</code> or <code z80>SYSSUK    INDEXW
-DW       (base address)</code>|
-| 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 |
-{{indexw.png}}
-==== MOVE ====
-MOVE BYTES
-| Calling Sequence: | <code z80>SYSTEM    MOVE</code> or <code z80>SYSSUK    MOVE
-DW       (destination)
-DW       (number of bytes)
-DW       (source)</code>|
-| 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 ====
-==== QUIT ====
-==== RANGED ====
-RANGED RANDOM NUMBER
-| Calling Sequence: | <code z80>SYSTEM    RANGED</code> or <code z80>SYSSUK    RANGED
-DB       (N)</code>|
-| 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 rom#system ram memory cells|system RAM]]. RANGED is called in [[human interface#getnum|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: | <code z80>SYSTEM    SETB</code> or <code z80>SYSSUK    SETB
-DB       (value to store)
-DW       (address)</code>|
-| 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: | <code z80>SYSTEM    SETW</code> or <code z80>SYSSUK    SETW
-DW       (value to store)
-DW       (address)</code>|
-| 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: | <code z80>SYSTEM    ????</code>|
-| Arguments: |  |
-| Notes: | Currently undocumented |
-| Description: | Shift up digit in A |
-| Restrictions: | None |
-==== STOREN ====
-STORE NIBBLE
-| Calling Sequence: | <code z80>SYSTEM    STOREN</code> or <code z80>SYSSUK    STOREN
-DW       (base address)</code>|
-| Arguments: | C = Nibble displacement (not loaded)\\ HL = Base address\\ A = Nibble value to store (not loaded) |
-| Notes: | None |
-| Description: | STOREN is the inverse of [[math routines#indexn|INDEXN]] but functions identically. |
-| Restrictions: | None |