Motorola DSP56800 Manual page 203

; Four-Quadrant Division of Fractional, Signed Data (B1:B0 / X0)
; Generates signed quotient and remainder
; Setup
MOVE
MOVE
ABS
EOR
BFCLR
; Division
REP
DIV
; Correct quotient
TFR
BGE
NEG
QDONE
MOVE
MOVE
ABS
ADD
BRCLR
MOVE
NEG
DONE
; Four-Quadrant Division of Integer, Signed Data (B1:B0 / X0)
; Generates signed quotient and remainder
; Setup
ASL
MOVE
MOVE
ABS
EOR
BFCLR
;Division
REP
DIV
; Correct quotient
TFR
BGE
NEG
QDONE
MOVE
MOVE
ABS
ADD
BRCLR
MOVE
NEG
ASR
DONE
B1,A ;Save sign bit of dividend (B1) in MSB of A1
B1,N ;Save sign bit of dividend (B1) in MSB of N
B ;Force dividend positive
X0,Y1 ;Save sign bit of quotient in N bit of SR
#$0001,SR ;Clear carry bit: required for first DIV instruction
16
X0,B
B,A
QDONE ;If correct result is positive, then done
B ; Else negate to get correct negative result
A0,Y1 ;Y1 <- True quotient
X0,A ;A <- Signed divisor
A ;A <- Absolute value of divisor
B,A ;A1 <- Restored remainder
#$8000,N,DONE
#0,A0
A
;(At this point, the correctly signed
; quotient is in Y1 and the correct
; remainder in A1)
B ;Shift of dividend required for integer
; division
B1,A ;Save sign bit of dividend (B1) in MSB of A1
B1,N ;Save sign bit of dividend (B1) in MSB of N
B ;Force dividend positive
X0,Y1 ;Save sign bit of quotient in N bit of SR
#$0001,SR ;Clear carry bit: required for first DIV instruction
16
X0,B
B,A
QDONE ;If correct result is positive, then done
B ; Else negate to get correct negative result
A0,Y1 ;Y1 <- True quotient
X0,A ;A <- Signed divisor
A ;A <- Absolute Value of divisor
B,A ;A1 <- Restored remainder
#$8000,N,DONE
#0,A0
A
B ;Shift required for correct integer remainder
;(At this point, signed quotient in Y1, correct
; remainder in A1)
Software Techniques
Division
8-17