Quadratic Solver in HC12 Assembly

main.asm

;*******************************************************************
;* author: Billy Lindeman & Christine Martin                       *
;* date:   8-23-2011                                               *
;* purpose: The purpose of this lab is to create a subroutine that *
;* calculates the real roots of a second order equation using the  *
;* quadratic formula                                               *
;* inputs: a,b,c as 8-bit signed integers                          *
;* outputs: both real roots of the quadratic equation              *
;*******************************************************************
; Include derivative-specific definitions
            INCLUDE 'derivative.inc'

; export symbols
            XDEF Entry, _Startup, main
            ; we use export 'Entry' as symbol. This allows us to
            ; reference 'Entry' either in the linker .prm file
            ; or from C/C++ later on

            XREF __SEG_END_SSTACK      ; symbol defined by the linker for the end of the stack


; variable/data section
MY_EXTENDED_RAM: SECTION
; Insert internal variables here
            ORG  $3900
            error_flag:  dc.b  1
            root1:       dc.w  1
            root2:       dc.w  1
            in_a:           dc.b  1
            in_b:           dc.b  1
            in_c:           dc.b  1


; code section - don't mess with anything from here...
MyCode:     SECTION
main:
_Startup:
Entry:
            LDS   #$3600
            LDAA  in_a                 
            PSHA  
            LDAA  in_b                 
            PSHA  
            LDAA  in_c                 
            PSHA  
            JSR   quadratic

			LEAS  3,SP
			LDAA  #$01    			             
            PSHA  
            LDAA  #$FC                 
            PSHA  
            LDAA  #$EB                 
            PSHA  
            JSR   quadratic
			
            JMP   endmain


quaderror:                          ;stack (a),(b),(c),[return]
            MOVB  #$FF,error_flag
            RTS  
det_lt_zero:                        ;stack (a),(b),(c),[return],[determinant],[-b],[2a]
            LEAS  8,SP              ;stack (a),(b),(c),[return]
            BRA   quaderror            
quadratic:
            LDAA  4,SP              ;load a -> a
            CMPA  #$00                
            BEQ   quaderror           
            
            LDD   #0                ;clear d
            LDY   #0                ;clear y
            LDAB  2,SP              ;load c->b
            SEX   B,Y               ;signextension in y
            LDAB  4,SP              ;load a->b
            SEX   B,D               ;signextension in d
            EMULS
            LDY   #$0004            ;y=4
            EMULS
            PSHD                    ;stack a,b,c,(4*a*c)(2b)
            LDAB  5,SP              ;load b->b
            SEX   B,Y               ;sign extend b into y
            SEX   B,D               ;sign extend b into d
            EMULS                   ;multiply d*y ->d
            PSHD                    ;stack a,b,c,[return](2b),(4*a*c)(2b),(b*b)(2b)
            LDD   0,SP              ;load  b*b into D
            SUBD  2,SP              ;subtract 4*a*c from b*b
            LEAS  4,SP
            PSHD                    ;stack (a),(b),(c),[return],[determinant]
            
            LDD   #0
            LDAB  5,SP              ;load b->d
            SEX   B,D               ;sign extend
            LDY   #$FFFF            ;load -1 -> y
            EMULS                   ;b*-1->d
            PSHD                    ;stack (a),(b),(c),[return],[determinant],[-b]
            
            LDD   #0               
            LDAB  8,SP              ;load a->b
            SEX   B,D
            LDY   #$0002            ;load 2->y
            EMULS                   ;2*a->d
            PSHD                    ;stack (a),(b),(c),[return],[determinant],[-b],[2a]
            
            LDD   4,SP
            CPD   #$0000
            BLT   det_lt_zero       ;if d<0, error out
            CPD   #$0000            ;
            BEQ   det_is_zero       ;if d = 0, one root
            BRA   det_gt_zero       ;if d > 0, two roots
        
det_is_zero:                        ;stack (a),(b),(c),[return],[determinant],[-b],[2a]
            LDD   2,SP
            LDX   0,SP
            IDIVS
            MOVB  #$00,error_flag
            STD   root1
            LEAS  8,SP
            RTS

det_gt_zero:                        ;stack (a),(b),(c),[return],[determinant],[-b],[2a]
            LDD   4,SP
            JSR   sqrt
            PSHD                    ;stack (a),(b),(c),[return],[determinant],[-b],[2a],[sqrt(det)]
            LDD   4,SP
            SUBD  0,SP
            LDX   2,SP
            IDIVS
            STX   root1
            LDD   4,SP
            ADDD  0,SP
            LDX   2,SP
            IDIVS
            STX   root2
            LEAS  8,SP
            RTS

                    
sqrt		    PSHD
  		      LDD   #0
			      PSHD
sqrtloop	  CPD		2,SP
	  		    BHI		donesqrt
		  	    ADDD	0,SP
		  	    INC		1,SP
		  	    ADDD	0,SP
		  	    BRA		sqrtloop
donesqrt	  PULD
    		  	DECB
		    	  LEAS	2,SP
			      RTS
	
endmain:     BRA endmain                ; end of program