Multibyte Arithmetic Assembly Library for PIC Microcontrollers

[Get source code] [Detailed information] [Other PIC projects] [Ben Jackson's PIC18F Macros]

I've been working on a couple of PIC microcontroller projects that require basic multi-byte arithmetical operations - addition, subtraction, multiplication, and division. Various projects require different number of bytes for each operand. Doing binary math in assembly language is lot of fun, so I wrote a small library with the following subroutines:

Multibyte addition and subtraction

Multibyte multiplication

Multibyte division and modulus (remainder)

Logical operations (multibyte increment, decrement, rotation to the left and right, clear)

PIC16F84A working on a long division

All operations are performed using three N-byte registers, as shown below. [Note that in memory the registers are ordered with the least significant byte coming first.]

`REG_X`	`byte N-1`	`...`	`byte 2`	`byte 1`	`byte 0`
`REG_Y`	`byte N-1`	`...`	`byte 2`	`byte 1`	`byte 0`
`REG_Z`	`byte N-1`	`...`	`byte 2`	`byte 1`	`byte 0`

The library has been tested with PIC16F688 microcontroller, but I see no reason why it shouldn't work on any 8-bit Microchip microcontroller. If you are looking for PIC18F multiplication/division, check out the macros on Ben Jackson's page.

Downloading the Library

To generate customized math library code that fits your project requirements, use the form below:

1. Select register size: N = bytes

2. Choose subroutines you need:

(NOTE: There are interdependencies between subroutines. For example, the multiplication subroutine requires the addition and rotation subroutines. Such dependencies are automatically resolved, so if a subroutine that is not selected by you is required, it will be included in the generated code nevertheless.)

Subroutine Description Details

M_ADD Addition [click]

M_SUB Subtraction [click]

M_MUL Multiplication [click]

M_DIV Division and modulus [click]

M_CMP Compare two registers [click]

M_INC Increment register [click]

M_DEC Decrement register [click]

M_ROL Rotate register to the left [click]

M_ROR Rotate register to the right [click]

M_TEST All of above + test subroutine [click]

3. Press button:

Detailed descriptions of the subroutines

The list below contains usage information and details for each subroutine.

M_ADD X + Z -> Z Calculate the sum of registers Z and X. Result is stored back in register Z.

M_SUB Z - X -> Z Subtract register X from register Z. Result is stored back in register Z.

M_MUL X * Y -> Z Multiplies register X with register Y. Result is stored in register Z.

M_DIV Z / X -> Y
Z mod X -> Z Divide register Z to register X. Result is stored in register Y. Remainder (modulus) of the division is stored in register Z.

M_CMP Z <=> X -> STATUS Compare registers Z and X. Comparison results are returned in the STATUS register. If register Z==X, the Z-bit of the STATUS register is set. If register Z=>X, the C-bit of the STATUS register is set.

M_INC REG + 1 -> REG Increment a register. The address of the register is passed to the subroutine in WREG. For example, to increment the X register, store REG_X's address in WREG and call M_INC:

movlw REG_X call M_INC

M_DEC REG - 1 -> REG Decrement a register. The address of the register is passed to the subroutine in WREG. For example, to decrement the Y register, store REG_Y's address in WREG and call M_DEC:

movlw REG_Y call M_DEC

M_ROL REG << 1 -> REG Rotate a register to the left. The address of the register is passed to the subroutine in WREG. For example, to rotate the Z register, store REG_Z's address in WREG and call M_ROL:

movlw REG_Z call M_ROL

M_ROR REG >> 1 -> REG Rotate a register to the right. The address of the register is passed to the subroutine in WREG. For example, to rotate the X register, store REG_X's address in WREG and call M_ROR:

movlw REG_Z call M_ROR

M_TEST If you select this option, a complete program with a test subroutine will be generated. All other subroutines will be included in the code. You can run the program in a debugger to experiment with the different subroutines, or use it as a starting template for your project code.

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