;////////////////////////////Test Driver//////////////
; This program includes the division function as well |
; as a driver to test the function. The driver should |
; also be used as a template for implimentation in    |
; other programs as R28 and R29 will be set to their  |
; values previous to the function call.  This program |
; needs to be run in conjunction with the aghar       |
; assemblier and linker.                              |
;                                                     |
; Author: William Martin                              |
;                                                     |
; Date: 3/2/2000                                      |
;                                                     |
; Input: Numerator (Register 28) and denominator      |
;        (Register 29). [keyboard in this driver]     |
; Output: Register 30 (answer of div. funct.)         |
;/////////////////////////////////////////////////////
.bss
             num: .reserve 4      ;to reset regs. later
             den: .reserve 4
.text
             INPUT R28            ;get numerator
             INPUT R29            ;get denominator
             STORE.w num, R28     ;save reg values
             STORE.w den, R29
             BL R31, divide       ;call to function
             NOP
             DUMP R30             ;put answer
             LOAD.w R28, num      ;reset registers
             LOAD.w R29, den
             NOP
             STOP
             NOP
;////////////////////////////Divide Function/////////
; This function will provide a division operation.    |
; Call this function with "BL R31, divide"            |
;                                                     |
; Author: William Martin                              |
;                                                     |
; Date: 3/5/2000                                      |
;                                                     |
; Preconditions: Numerator in Register 28 and         |
;                Denominator in Register 29           |
; Postconditions: Answer in register 30, if zero      |
;                 denominator than program will quit  |
;                 with a error value in register 30   |
;/////////////////////////////////////////////////////
.data
             .equate error, 2147483646 ;max value
.bss
     temp:   .reserve 4             ;to store R1
.text
   divide:   MOVE R30, R0           ;initialize answer
             STORE.w temp, R1       ;save R1 value
             MOVE R1, R0            ;initialize flag
             BREQ R29, R0, err      ;if 0 den. than error
 test_num:   BRGT R28, #0, test_den ;if neg. than flag
             NOP
             NEG R28, R28           ;make absolute value
             ADD R1, #1, R1         ;flag
 test_den:   BRGT R29, #0, loop_top ;if neg. than flag
             NOP
             NEG R29, R29           ;make absolute value
             SUB R1, #1, R1         ;flag, if flagged, unflag
 loop_top:   BRLT R28, R29, bottom  ;while num<den loop
             SUB R28, R28, R29      ;num - den
             ADD R30, R30, #1       ;answer + 1
             BRANCH loop_top
             NOP
   bottom:   BREQ R1, R0, done      ;if no flag, done
             NOP
             NEG R30, R30           ;if flag, ans is - val.
     done:   LOAD.w R1, temp        ;reset register 1
             BRANCH R31             ;return to function caller
             NOP
      err:   MOVE R30, #error       ;catch zero_denominator
             DUMP R30               ;return error value
             STOP                   ;halt program
             NOP
.end