Optimizing DIV

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  1. - 10th August 2008, 09:20 #1
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    Quote Originally Posted by Darrel Taylor View Post
    This doesn't quite follow the Italics section, but I think It's what you meant...................
    Does it look like what you were thinking?
    <br>
    I was going to handle it today but got sidetracked with a bunch of welding/fabricating.

    Yep, that's pretty much exactly what I was thinking and it would, by default, kick out of the shifting loop if either R0/R1 was 'negative'.
    Then just test it out by doing LONG divides in a loop ( 0 thru 2^31, looping the divisor inside another loop for the dividend, would take a LONG-LONG time even at 40Mhz ), save the result and remainder, remultiply (which obviously hasn't been modified) add the remainder back in and see if that result is the same as the original integer. That should verify everything works correctly. After that, rewrite the code to break it down by bits instead of bytes.
    Should end up to be a significant speed increase and a relatively simple cut-and-paste into the .lib file...
  2. - 7th September 2008, 10:18 #2
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    Code:
    ;****************************************************************
;* DIV        : 32 x 32 divide                                  *
;* Input      : R0 / R1                                         *
;* Output     : R0 = quotient                                   * 
;*            : R2 = remainder                                  *
;* Notes      : R2 = R0 MOD R1                                  *
;****************************************************************

    ifdef DIVS_USED
  LIST
DIVS	clrf	R3 + 3		; Clear sign difference indicator
	btfss	R0 + 3, 7	; Check for R0 negative
	bra	divchkr1	; Not negative
	btg	R3 + 3, 7	; Flip sign indicator
	clrf	WREG		; Clear W for subtracts
	negf	R0		; Flip value to plus
	subfwb	R0 + 1, F
	subfwb	R0 + 2, F
	subfwb	R0 + 3, F
divchkr1 btfss	R1 + 3, 7	; Check for R1 negative
	bra	divdo		; Not negative
	btg	R3 + 3, 7	; Flip sign indicator
	clrf	WREG		; Clear W for subtracts
	negf	R1		; Flip value to plus
	subfwb	R1 + 1, F
	subfwb	R1 + 2, F
	subfwb	R1 + 3, F
	bra	divdo		; Skip unsigned entry
  NOLIST
DIV_USED = 1
    endif

    ifdef DIV_USED
  LIST
DIV
      ifdef DIVS_USED
	clrf	R3 + 3		; Clear sign difference indicator	
      endif
divdo	clrf	R2		; Do the divide
	clrf	R2 + 1
	clrf	R2 + 2
	clrf	R2 + 3

	movlw	32             ; start with 32 loops
	movwf	R3

        ifdef SKI_DIV_SPEEDUP
SkiOpt
	movf    R0 + 3, W      ; IF R0.byte3 = 0 
	bnz     divloop
	movf    R1 + 3, W      ;   AND R1.byte3 = 0 then 
	bnz     divloop

	movlw   8              ;      loops - 8  ; movlw 24
	subwf   R3, F

	movff   R0 + 2, R0 + 3 ;      and preshift R0
	movff   R0 + 1, R0 + 2
	movff   R0 + 0, R0 + 1
	clrf    R0

	movff   R1 + 2, R1 + 3 ;      and R1 over 8 bits
	movff   R1 + 1, R1 + 2
	movff   R1 + 0, R1 + 1
	clrf    R1

	movf    R3, W
	btfss   STATUS, Z      ; stop if no loop's left (0/0)
	bra     SkiOpt

        endif

divloop	rlcf	R0 + 3, W
	rlcf	R2, F
	rlcf	R2 + 1, F
	rlcf	R2 + 2, F
	rlcf	R2 + 3, F
	movf	R1, W
	subwf	R2, F
	movf	R1 + 1, W
	subwfb	R2 + 1, F
	movf	R1 + 2, W
	subwfb	R2 + 2, F
	movf	R1 + 3, W
	subwfb	R2 + 3, F

	bc	divok
	movf	R1, W
	addwf	R2, F
	movf	R1 + 1, W
	addwfc	R2 + 1, F
	movf	R1 + 2, W
	addwfc	R2 + 2, F
	movf	R1 + 3, W
	addwfc	R2 + 3, F

	bcf	STATUS, C

divok	rlcf	R0, F
	rlcf	R0 + 1, F
	rlcf	R0 + 2, F
	rlcf	R0 + 3, F

	decfsz	R3, F
	bra	divloop

      ifdef DIVS_USED
	btfss	R3 + 3, 7	; Should result be negative?
	bra	divdone		; Not negative
	clrf	WREG		; Clear W for subtracts
	negf	R0		; Flip quotient to minus
	subfwb	R0 + 1, F
	subfwb	R0 + 2, F
	subfwb	R0 + 3, F
	negf	R2		; Flip remainder to minus
	subfwb	R2 + 1, F
	subfwb	R2 + 2, F
	subfwb	R2 + 3, F
divdone
    endif

	movf	R0, W		; Get low byte to W
	goto	DUNN
  NOLIST
DUNN_USED = 1
    endif
    This optimization (byte level optimize) seems to work very well on my end using MPLAB sim and the stopwatch.
    I've got to finish up a 2nd demo board with an LCD, one running the non-optimized version, one running the optimized version, just to see which one counts faster and by how much.
    I still want to change the optimization down to the bit level and have the library recognize the DEFINE as none (not defined), byte or bit.
    How do you get MPASM to recognize different parameters using DEFINE in PBP? I can't seem to get it to work right...
  3. - 7th September 2008, 22:45 #3
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    Quote Originally Posted by skimask View Post
    How do you get MPASM to recognize different parameters using DEFINE in PBP? I can't seem to get it to work right...
    Several ways ... here's one.

    Code:
    DEFINE  OptLevel  BYTE

ASM
BIT = 1
BYTE = 8
WORD = 16
LONG = 32

    IFDEF OptLevel  
        IF (OptLevel == BYTE)
            ; -- Byte level specified
        ENDIF
        IF (OptLevel == WORD)
            ; -- Word level specified
        ENDIF
    ENDIF
ENDASM
    DT
  4. - 8th September 2008, 00:48 #4
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    Quote Originally Posted by Darrel Taylor View Post
    Several ways ... here's one.
    Noticed that this morning when I looked thru a couple of my .LST files.
    Not sure if my problem was the missing parentheses or the double-equal in the IF statement.

    My next step is to 'include' various levels of 32 bit divide optimization, none, byte, and bit level
    i.e.
    DEFINE SKI_DIV_OPT BYTE (speeds up divides 8 bits at a time)
    DEFINE SKI_DIV_OPT BIT (speeds up divides at the bit level)
  5. - 8th September 2008, 02:15 #5
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    Ok, did some fooling around with the divide optimizations...
    This looks like it should work...
    Code:
    ;****************************************************************
;* DIV        : 32 x 32 divide                                  *
;*                                                              *
;* Input      : R0 / R1                                         *
;* Output     : R0 = quotient                                   * 
;*            : R2 = remainder                                  *
;*                                                              *
;* Notes      : R2 = R0 MOD R1                                  *
;****************************************************************

    ifdef DIVS_USED
  LIST
DIVS	clrf	R3 + 3		; Clear sign difference indicator
	btfss	R0 + 3, 7	; Check for R0 negative
	bra	divchkr1	; Not negative
	btg	R3 + 3, 7	; Flip sign indicator
	clrf	WREG		; Clear W for subtracts
	negf	R0		; Flip value to plus
	subfwb	R0 + 1, F
	subfwb	R0 + 2, F
	subfwb	R0 + 3, F
divchkr1 btfss	R1 + 3, 7	; Check for R1 negative
	bra	divdo		; Not negative
	btg	R3 + 3, 7	; Flip sign indicator
	clrf	WREG		; Clear W for subtracts
	negf	R1		; Flip value to plus
	subfwb	R1 + 1, F
	subfwb	R1 + 2, F
	subfwb	R1 + 3, F
	bra	divdo		; Skip unsigned entry
  NOLIST
DIV_USED = 1
    endif

    ifdef DIV_USED
  LIST
DIV
      ifdef DIVS_USED
	clrf	R3 + 3		; Clear sign difference indicator	
      endif
divdo	clrf	R2		; Do the divide
	clrf	R2 + 1
	clrf	R2 + 2
	clrf	R2 + 3

	movlw	32
	movwf	R3

;added to speed up s-31 bit divide operations by ignoring
;zero'd bytes
        ifdef SKI_DIV_OPT
		if ( SKI_DIV_OPT == 1 )
SkiOpt
	movf    R0 + 3, W      ; IF R0.byte3 = 0 
	bnz     divloop
	movf    R1 + 3, W      ;   AND R1.byte3 = 0 then 
	bnz     divloop

	movlw   8              ;      loops - 8  ; movlw 24
	subwf   R3, F

	movff   R0 + 2, R0 + 3 ;      and preshift R0
	movff   R0 + 1, R0 + 2
	movff   R0 + 0, R0 + 1
	clrf    R0

	movff   R1 + 2, R1 + 3 ;      and R1 over 8 bits
	movff   R1 + 1, R1 + 2
	movff   R1 + 0, R1 + 1
	clrf    R1

	movf    R3, W
	btfss   STATUS, Z      ; stop if no loop's left (0/0)
	bra     SkiOpt
		endif
        endif

;above added to speed divide operations

;added to speed up s-31 bit divides by skipping cleared bits in divisor/dividend
	ifdef SKI_DIV_OPT
		if ( SKI_DIV_OPT == 2 )
SkiOpt2
	btfsc	R0 + 3, 7	; if highest bit set, goto divloop
	bra	divloop
	btfsc	R1 + 3, 7	; if highest bit set, goto divloop
	bra	divloop

;streamlined code here...old stuff is gone...
	bsc	status, 0	;clear carry - shift over complete R0
	rlcf	R0, F		;shift R0, .7 into carry
	rlcf	R0 + 1, F	;shift R0+1
	rlcf	R0 + 2, F	;shift R0+2
	rlcf	R0 + 3, F	;shift R0+3

	bsc	status, 0	;clear carry - shift over complete R1
	rlcf	R1, F		;shift R1, .7 into carry
	rlcf	R1 + 1, F	;shift R1+1
	rlcf	R1 + 2, F	;shift R1+2
	rlcf	R1 + 3, F	;shift R1+3

	movlw	1		;subtract one from the loop count
	subwf	R3, F

	movf	R3, W
	btfss STATUS, Z	;stop if no more loops
	bra	SkiOpt2

		endif
	endif
;above added to speed up divides at the bit level

divloop	rlcf	R0 + 3, W
	rlcf	R2, F
	rlcf	R2 + 1, F
	rlcf	R2 + 2, F
	rlcf	R2 + 3, F
	movf	R1, W
	subwf	R2, F
	movf	R1 + 1, W
	subwfb	R2 + 1, F
	movf	R1 + 2, W
	subwfb	R2 + 2, F
	movf	R1 + 3, W
	subwfb	R2 + 3, F

	bc	divok
	movf	R1, W
	addwf	R2, F
	movf	R1 + 1, W
	addwfc	R2 + 1, F
	movf	R1 + 2, W
	addwfc	R2 + 2, F
	movf	R1 + 3, W
	addwfc	R2 + 3, F

	bcf	STATUS, C

divok	rlcf	R0, F
	rlcf	R0 + 1, F
	rlcf	R0 + 2, F
	rlcf	R0 + 3, F

	decfsz	R3, F
	bra	divloop

      ifdef DIVS_USED
	btfss	R3 + 3, 7	; Should result be negative?
	bra	divdone		; Not negative
	clrf	WREG		; Clear W for subtracts
	negf	R0		; Flip quotient to minus
	subfwb	R0 + 1, F
	subfwb	R0 + 2, F
	subfwb	R0 + 3, F
	negf	R2		; Flip remainder to minus
	subfwb	R2 + 1, F
	subfwb	R2 + 2, F
	subfwb	R2 + 3, F
divdone
    endif

	movf	R0, W		; Get low byte to W
	goto	DUNN
  NOLIST
DUNN_USED = 1
    endif
    See any glaring problems?
    I'm still a bit fuzzy on using the DEFINEs in PBP and relating them to the assembler though, so not sure if that will work.
    And, with the bit level optimization, I'm not sure that'll save any time anyways.
    More testing to come...
    Last edited by skimask; - 8th September 2008 at 03:06. Reason: Streamlined code a bit, changed shift from hi->low, to low->high by using carry bit...
  6. - 11th September 2008, 03:55 #6
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    Well, looks like it may need something else.

    I wrapped it in a program, and changed the labels so it would coexist with PBP, then used a couple FOR loops to cycle through some numbers. It does the optimized divide, then does a normal PBP divide and compares the results. If they aren't the same, is sends a message out the USART.

    With the DEFINE SKI_DIV_OPT line commented out, both versions are always the same. Which shows that the test program is working, and the output looks like this ...
    Code:
    A=93  No ERRORs
A=94  No ERRORs
A=95  No ERRORs
A=96  No ERRORs
A=97  No ERRORs
A=98  No ERRORs
A=99  No ERRORs
A=100  No ERRORs
A=101  No ERRORs
A=102  No ERRORs
A=103  No ERRORs
A=104  No ERRORs
    With SKI_DIV_OPT defined as either 1 or 2, the results are the same. Here's some output from SKI_DIV_OPT 1 ...
    Code:
     Quotient Error: A=59  B=51  Ski=0  PBP=1
Remainder Error: A=59  B=51  Ski=59  PBP=8
 Quotient Error: A=59  B=52  Ski=0  PBP=1
Remainder Error: A=59  B=52  Ski=59  PBP=7
 Quotient Error: A=59  B=53  Ski=0  PBP=1
Remainder Error: A=59  B=53  Ski=59  PBP=6
 Quotient Error: A=59  B=54  Ski=0  PBP=1
Remainder Error: A=59  B=54  Ski=59  PBP=5
 Quotient Error: A=59  B=55  Ski=0  PBP=1
Remainder Error: A=59  B=55  Ski=59  PBP=4
 Quotient Error: A=59  B=56  Ski=0  PBP=1
Remainder Error: A=59  B=56  Ski=59  PBP=3
 Quotient Error: A=59  B=57  Ski=0  PBP=1
Remainder Error: A=59  B=57  Ski=59  PBP=2
 Quotient Error: A=59  B=58  Ski=0  PBP=1
Remainder Error: A=59  B=58  Ski=59  PBP=1
 Quotient Error: A=59  B=59  Ski=0  PBP=1
Remainder Error: A=59  B=59  Ski=59  PBP=0
 Quotient Error: A=60  B=0  Ski=255  PBP=4294967295
 Quotient Error: A=60  B=1  Ski=0  PBP=60
Remainder Error: A=60  B=1  Ski=60  PBP=0
 Quotient Error: A=60  B=2  Ski=0  PBP=30
Remainder Error: A=60  B=2  Ski=60  PBP=0
 Quotient Error: A=60  B=3  Ski=0  PBP=20
Remainder Error: A=60  B=3  Ski=60  PBP=0
 Quotient Error: A=60  B=4  Ski=0  PBP=15
Remainder Error: A=60  B=4  Ski=60  PBP=0
 Quotient Error: A=60  B=5  Ski=0  PBP=12
Remainder Error: A=60  B=5  Ski=60  PBP=0
 Quotient Error: A=60  B=6  Ski=0  PBP=10
Remainder Error: A=60  B=6  Ski=60  PBP=0
 Quotient Error: A=60  B=7  Ski=0  PBP=8
Remainder Error: A=60  B=7  Ski=60  PBP=4
 Quotient Error: A=60  B=8  Ski=0  PBP=7
Remainder Error: A=60  B=8  Ski=60  PBP=4
 Quotient Error: A=60  B=9  Ski=0  PBP=6
Remainder Error: A=60  B=9  Ski=60  PBP=6
 Quotient Error: A=60  B=10  Ski=0  PBP=6
Remainder Error: A=60  B=10  Ski=60  PBP=0
 Quotient Error: A=60  B=11  Ski=0  PBP=5
Remainder Error: A=60  B=11  Ski=60  PBP=5
 Quotient Error: A=60  B=12  Ski=0  PBP=5
Remainder Error: A=60  B=12  Ski=60  PBP=0
 Quotient Error: A=60  B=13  Ski=0  PBP=4
    Here's the program, any 18F will do ...
    Code:
    '****************************************************************
'*  Name    : Test_SkiDIV.pbp                                   *
'*  Author  : Darrel Taylor                                     *
'*  Date    : 9/9/2008                                          *
'*  Version : 1.0                                               *
'*  Thread  : instruction execution time                        *
'*      http://www.picbasic.co.uk/forum/showthread.php?p=61992  *
'****************************************************************
;****************************************************************
;* DIV        : 32 x 32 divide                                  *
;*                                                              *
;* Input      : R0 / R1                                         *
;* Output     : R0 = quotient                                   * 
;*            : R2 = remainder                                  *
;*                                                              *
;* Notes      : R2 = R0 MOD R1                                  *
;****************************************************************

DEFINE OSC 40

DEFINE HSER_TXSTA 24h 'Hser transmit status init 
DEFINE HSER_RCSTA 90h 'Hser receive status init 
DEFINE HSER_BAUD 38400 'Hser baud rate 
DEFINE HSER_CLROERR 1 'Hser clear overflow automatically 
 
DEFINE SKI_DIV_OPT 1

AL    VAR LONG
BL    VAR LONG
SkiQ  VAR LONG   ; ASM quotient
SkiR  VAR LONG   ; ASM remainder

PBPQ  VAR LONG   ; PBP quotient
PBPR  VAR LONG   ; PBP remainder

AW  VAR WORD
BW  VAR WORD
RW  VAR WORD

ERROR VAR BIT

For AL = 0 to 1000
    ERROR = 0
    For BL = 0 to 1000
        @ MOVE?NN  _AL, R0
        @ MOVE?NN  _BL, R1  ; AL / BL
        @ L?CALL   #DIVS
        @ MOVE?ANN R0, _SkiQ
        @ MOVE?NN  R2, _SkiR
        PBPQ = AL / BL                   ; do same in PBP
        PBPR = AL // BL
        
        if SkiQ != PBPQ then 
            HSEROUT [" Quotient Error: A=",DEC AL,"  B=",DEC BL, _
                     "  Ski=",dec SkiQ,"  PBP=",DEC PBPQ,13,10]
            ERROR = 1
        endif
        if SkiR != PBPR then 
            HSEROUT ["Remainder Error: A=",DEC AL,"  B=",DEC BL, _
                     "  Ski=",dec SkiR,"  PBP=",DEC PBPR,13,10]
            ERROR = 1
        endif
    next BL
    if ERROR = 0 then HSEROUT ["A=",dec AL,"  No ERRORs",13,10]
next AL

stop

; -------------------
ASM
    ifdef DIVS_USED
  LIST
#DIVS  clrf	R3 + 3		; Clear sign difference indicator
	btfss	R0 + 3, 7	; Check for R0 negative
	bra	#divchkr1	; Not negative
	btg	R3 + 3, 7	; Flip sign indicator
	clrf	WREG		; Clear W for subtracts
	negf	R0		; Flip value to plus
	subfwb	R0 + 1, F
	subfwb	R0 + 2, F
	subfwb	R0 + 3, F
#divchkr1  btfss	R1 + 3, 7	; Check for R1 negative
	bra	#divdo		; Not negative
	btg	R3 + 3, 7	; Flip sign indicator
	clrf	WREG		; Clear W for subtracts
	negf	R1		; Flip value to plus
	subfwb	R1 + 1, F
	subfwb	R1 + 2, F
	subfwb	R1 + 3, F
	bra	#divdo		; Skip unsigned entry
  NOLIST
DIV_USED = 1
    endif

    ifdef DIV_USED
  LIST
#DIV
      ifdef DIVS_USED
	clrf	R3 + 3		; Clear sign difference indicator	
      endif
#divdo	clrf	R2		; Do the divide
	clrf	R2 + 1
	clrf	R2 + 2
	clrf	R2 + 3

	movlw	32
	movwf	R3

;added to speed up s-31 bit divide operations by ignoring
;zero'd bytes
        ifdef SKI_DIV_OPT
		if ( SKI_DIV_OPT == 1 )
SkiOpt
	movf    R0 + 3, W      ; IF R0.byte3 = 0 
	bnz     #divloop
	movf    R1 + 3, W      ;   AND R1.byte3 = 0 then 
	bnz     #divloop

	movlw   8              ;      loops - 8  ; movlw 24
	subwf   R3, F

	movff   R0 + 2, R0 + 3 ;      and preshift R0
	movff   R0 + 1, R0 + 2
	movff   R0 + 0, R0 + 1
	clrf    R0

	movff   R1 + 2, R1 + 3 ;      and R1 over 8 bits
	movff   R1 + 1, R1 + 2
	movff   R1 + 0, R1 + 1
	clrf    R1

	movf    R3, W
	btfss   STATUS, Z      ; stop if no loop's left (0/0)
	bra     SkiOpt
		endif
        endif

;above added to speed divide operations

;added to speed up s-31 bit divides by skipping cleared bits in divisor/dividend
	ifdef SKI_DIV_OPT
		if ( SKI_DIV_OPT == 2 )
SkiOpt2
	btfsc	R0 + 3, 7	; if highest bit set, goto divloop
	bra	#divloop
	btfsc	R1 + 3, 7	; if highest bit set, goto divloop
	bra	#divloop

;streamlined code here...old stuff is gone...
	bcf    	STATUS, 0	;clear carry - shift over complete R0
	rlcf	R0, F		;shift R0, .7 into carry
	rlcf	R0 + 1, F	;shift R0+1
	rlcf	R0 + 2, F	;shift R0+2
	rlcf	R0 + 3, F	;shift R0+3

;	bsc	status, 0	;clear carry - shift over complete R1
	bcf	    STATUS, 0	;clear carry - shift over complete R1
	rlcf	R1, F		;shift R1, .7 into carry
	rlcf	R1 + 1, F	;shift R1+1
	rlcf	R1 + 2, F	;shift R1+2
	rlcf	R1 + 3, F	;shift R1+3

	movlw	1		;subtract one from the loop count
	subwf	R3, F

	movf	R3, W
	btfss STATUS, Z	;stop if no more loops
	bra	SkiOpt2

		endif
	endif
;above added to speed up divides at the bit level

#divloop	rlcf	R0 + 3, W
	rlcf	R2, F
	rlcf	R2 + 1, F
	rlcf	R2 + 2, F
	rlcf	R2 + 3, F
	movf	R1, W
	subwf	R2, F
	movf	R1 + 1, W
	subwfb	R2 + 1, F
	movf	R1 + 2, W
	subwfb	R2 + 2, F
	movf	R1 + 3, W
	subwfb	R2 + 3, F

	bc	#divok
	movf	R1, W
	addwf	R2, F
	movf	R1 + 1, W
	addwfc	R2 + 1, F
	movf	R1 + 2, W
	addwfc	R2 + 2, F
	movf	R1 + 3, W
	addwfc	R2 + 3, F

	bcf	STATUS, C

#divok	rlcf	R0, F
	rlcf	R0 + 1, F
	rlcf	R0 + 2, F
	rlcf	R0 + 3, F

	decfsz	R3, F
	bra	#divloop

      ifdef DIVS_USED
	btfss	R3 + 3, 7	; Should result be negative?
	bra	#divdone		; Not negative
	clrf	WREG		; Clear W for subtracts
	negf	R0		; Flip quotient to minus
	subfwb	R0 + 1, F
	subfwb	R0 + 2, F
	subfwb	R0 + 3, F
	negf	R2		; Flip remainder to minus
	subfwb	R2 + 1, F
	subfwb	R2 + 2, F
	subfwb	R2 + 3, F
#divdone
    endif

	movf	R0, W		; Get low byte to W
	goto	DUNN
  NOLIST
DUNN_USED = 1
    endif
ENDASM
    DT
  7. - 11th September 2008, 04:06 #7
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    You got to it before I could finish it up. I see what you've done.
    Yep, sure doesn't work! I did have it working though...at least in MPLAB's sim, watching registers come up the same. Never did finish up the 2nd LCD board...
    Question : I would've thought that using the pound sign in front of a label and for a label would jack up the assembler. This works as you've written?
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