Motorola DSP96002 - Manual (Page 714)

MOTOROLA DSP96002 USER’S MANUAL B-195
inc d0 ifcs ;if odd exponent, use 2 bits
add d2,d1 ;restore exponent bias
move d1.l,x:(r0) ;store it
move x:(r0+ms),d7.l ;get ms
move x:(r0+ls),d6.l ;get ls
clr d4 #0,d5.l ;clear RR
clr d3 #0,d2.l ;clear DR
do d0.l,_initshift ;initial shift
lsl d6 ;shift 2 bits from d7:d6 (SQR)
rol d7
rol d4 ;to d5:d4 (RR)
rol d5
_initshift
do #62,_sqrt ;take root of SQR into DR
lsl d2 d4.l,d0.l ;(dr<<2)|1, copy rr
rol d3 d5.l,d1.l
lsl d2
rol d3
inc d2 ;set lsb
sub d2,d0 ;temp=rr-(dr<<2)|1
subc d3,d1
jcs _ofl ;overflow
lsr d3 d0.l,d4.l ;shift dr back only 1 bit
ror d2 d1.l,d5.l ;rr=temp
inc d2 ;root bit=1
jmp _next
_ofl lsr d3 ;shift dr back only 1 bit
ror d2 ;root bit=0
_next lsl d6 ;shift 2 bits from d7:d6 (SQR)
rol d7
rol d4 ;to d5:d4 (RR)
rol d5
lsl d6 ;shift 2 bits from d7:d6 (SQR)
rol d7
rol d4 ;to d5:d4 (RR)
rol d5
_sqrt lsl d2 ;adjust to msb
rol d3
lsl d2 ;adjust to msb
rol d3
move d3.l,x:(r0+ms) ;save ms part
move d2.l,x:(r0+ls) ;save ls part
rts
;
; MOTOROLA DSP96002 DPLIB - VERSION 1.0
;
; DP_SUB - Double precision subtraction.
;
; Entry point: dp_sub: c(r0)
←
c(r0) - c(r1)
;
; Inputs: r0 contains the lowest address of a 4-word internal
; extended precision number
; r1 contains the lowest address of a 4-word internal