;------------------------------------------------------------------
; Mult 24 x 24 out 48 (max)
; Fred Maher 3rd Nov 2002
;------------------------------------------------------------------
; This routine is "slow" with 1.the big numbers and acceptable with
; a 2. small x big multiplication.
; Typical times
; 1. FFFFFF*EEDDCC = EEDDCB112234 1750 cycles 330usec
; 2. FFFFFF* F7 = F6FFFF09 650 cycles 130usec
LIST P=16F628 ; 16F628 Runs at 20 MHz
INCLUDE "p16F628.inc"
__CONFIG _CP_OFF & _WDT_OFF & _HS_OSC & _PWRTE_ON & _LVP_OFF & _BODEN_OFF
ERRORLEVEL -224 ; suppress annoying message because of tris
ERRORLEVEL -302 ; suppress message because of page change
CBLOCK 20H
top1
top2
top3
top4
top5
top6
bot1
bot2
bot3
res1
res2
res3
res4
res5
res6
count
temp
c1
c2
ENDC
movlw 0xF7
movwf top1
movlw 0x00
movwf top2
movlw 0x00
movwf top3
movlw 0x00
movwf top4
movlw 0x00
movwf top5
movlw 0x00
movwf top6
movlw 0xFF
movwf bot1
movlw 0xFF
movwf bot2
movlw 0xFF
movwf bot3
clrf res1
clrf res2
clrf res3
clrf res4
clrf res5
clrf res6
;-----------------------------------------------------------------------
; Mult24 is the main mult routine start point
;------------------------------------------------------------------------
Mult24: ;
bcf STATUS,DC
call Regcomp ; Puts smaller number into multiplier and finds count minimum.
nop
incf count,f
clrf res1
clrf res2
clrf res3
call X24 ; main 24 x 24 mult
Mult24end: ; here back to principal program with return, 2 lines below
goto Mult24end ; dummy instruction for testing that it multiplies
; return ; restore when using with main program
;--------------------------------------------------------------------------
; End of multiply 24 x 24 ; out 48, routine
;--------------------------------------------------------------------------
Regcomp: ; compare top and bot regs 3 2 1 to decide if we need to swap.
bcf STATUS,2
bcf STATUS,1
bcf STATUS,0
Test33:
movf bot3,w
subwf top3,w
btfsc STATUS,C ;
goto $+ 3 ; top is equal or bigger
call Swap
goto Leftbit ; find leftmost 1 for count.
; end case top>bot
clrw ; test top=0 (if top=0 then bot=0 (can't be minus))
xorwf top3,w
btfsc STATUS,Z
goto Test22 ; both zero, continue test with top2,bot2
goto Leftbit
Test22:
movf bot2,w
subwf top2,w
btfsc STATUS,C ;
goto $+ 3 ; top is equal or bigger
call Swap
goto Leftbit ; find leftmost 1 for count.
; end case top>bot
clrw ; test top=0 (if top=0 then bot=0 (can't be minus))
xorwf top2,w
btfsc STATUS,Z
goto Test11 ; both zero, continue test with top2,bot2
goto Leftbit
Test11:
movf bot1,w
subwf top1,w
btfsc STATUS,C ;
goto $+ 3 ; top is equal or bigger
call Swap
goto Leftbit ; find leftmost 1 for count.
; end case top>bot
clrw ; test top=0 (if top=0 then bot=0 (can't be minus))
xorwf top1,w
btfsc STATUS,Z
goto Test11 ; both zero, continue test with top2,bot2
movf bot1,w ;put bot in temp
movwf temp
movlw d'08' ; bot is smaller so set count to 24
movwf count ; do Leftbit
goto Leftbit
Swap:
movf top3,w
movwf res3
movf bot3,w
movwf top3
movf res3,w
movwf bot3
movf top2,w
movwf res2
movf bot2,w
movwf top2
movf res2,w
movwf bot2
movf top1,w
movwf res1
movf bot1,w
movwf top1
movf res1,w
movwf bot1
return
Leftbit:
;Now find in bot3,2,1 that which is not zero, find leftmost ONE
clrw
xorwf bot3,w
btfsc STATUS, Z
goto $+6
movf bot3,w
movwf temp
movlw d'24'
movwf count
goto Oneloop
clrw
xorwf bot2,w
btfsc STATUS, Z
goto $+6
movf bot2,w
movwf temp
movlw d'16'
movwf count
goto Oneloop
clrw
xorwf bot1,w
btfsc STATUS, Z
goto $+4
movf bot1,w
movwf temp
movlw d'08'
movwf count
goto Oneloop
Oneloop: ; We move through the 8 bits of temp from 8 to 1
btfsc temp,7
return
decf count,f
rlf temp,f
goto Oneloop
return ; to main mult
;----------------------------------------------------------------
; End of the compare / count routine
;----------------------------------------------------------------
X24: ; mult loop proper starts here with entered values
Step1: ; To add or not to add? that is the question.
btfss bot1,0
goto Step3 ; 0... don't add top to res
goto Step2 ; 1... add top to res
Step2: ; Adding top to res
;Note all credit to ****Dwayne Reid**** for this add routine
;much shorter and more elegant than my one.
movfw top1
addwf res1,f
movfw top2
skpnc
incfsz top2,w
addwf res2,f
movfw top3
skpnc
incfsz top3,w
addwf res3,f
movfw top4
skpnc
incfsz top4,w
addwf res4,f
movfw top5
skpnc
incfsz top5,w
addwf res5,f
movfw top6
skpnc
incfsz top6,w
addwf res6,f
Step3: ; Left shifting top
; This looks the same as an add but it is different
bcf STATUS,C
rlf top6,f
btfsc STATUS,C
nop
bcf STATUS,C
rlf top5,f
btfsc STATUS,C
incf top6,f
bcf STATUS,C
rlf top4,f
btfsc STATUS,C
incf top5,f
bcf STATUS,C
rlf top3,f
btfsc STATUS,C
incf top4,f
bcf STATUS,C
rlf top2,f
btfsc STATUS,C
incf top3,f
bcf STATUS,C
rlf top1,f
btfsc STATUS,C
incf top2,f
bcf STATUS,C
Stepend:
nop
Step4: ;Right shifting bottom and terminate loop for count = MAX, here 24.
decf count,f ; we start with count =24 OR speeded up count
clrw
xorwf count,w
btfsc STATUS,Z
RETURN ; count finished
; count not finished, continue Step4
rrf bot1,f
bcf STATUS,C
rrf bot2,f
btfss STATUS,C
goto $ + 4 ; there was no carry, jump forward 4
movlw 0x80
addwf bot1,f
bcf STATUS,C
rrf bot3,f
btfss STATUS,C
goto $ + 4 ; there was no carry, jump forward 4
movlw 0x80
addwf bot2,f
bcf STATUS,C
goto Step1
;---------------------------------------------------------------------
; End of reg multiplication
;---------------------------------------------------------------------
end
;------------------------------------------------------------------
; End Mult 24 x 24
;------------------------------------------------------------------
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