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Nibble Shift Code Help

Suraj143

Active Member
Thread starter #1
I have a 32 byte array & I want to shift its nibbles separately.
Means when I call the subroutine, it will shift the upper nibbles of the array left and shift their lower nibbles right.

Did a code but seems likes its too long :( need to optimize

Thanks

Code:
        cblock        30h
        C1,C2,C3,C4,C5,C6,C7,C8,C9,C10,C11,C12,C13,C14,C15,C16
        C17,C18,C19,C20,C21,C22,C23,C24,C25,C26,C27,C28,C29,C30,C31,C32        ;4Fh last byte
        endc       
               
Shift_Left                movlw    .32
                        movwf    Byte_Count
                        movlw    30h
                        movwf    FSR                       
                        movf    INDF,W
                        movwf    Copy_Last        ; save 1st byte                       
                       
Shift_Upper_Left        movf    INDF,W
                        andlw    b'00001111'        ; clear the upper nibble
                        movwf    INDF
                        incf    FSR,F
                        movf    INDF,W
                        andlw    b'11110000'        ; only move upper nibble
                        decf    FSR,F
                        iorwf    INDF,F
                        incf    FSR,F
                        decfsz    Byte_Count,F
                        goto    Shift_Upper_Left
                        movf    C32,W            ; last byte
                        andlw    b'00001111'
                        movwf    C32
                        movf    Copy_Last,W
                        iorwf    C32,F
;------------------------------------------------                       
Shift_Right                movlw    4Fh
                        movwf    FSR
                        movlw    .32
                        movwf    Byte_Count
                        movf    INDF,W
                        movwf    Copy_Last        ; save 1st byte   
                       
Shift_Lower_Right        movf    INDF,W
                        andlw    b'11110000'        ; clear the lower nibble
                        movwf    INDF
                        decf    FSR,F
                        movf    INDF,W
                        andlw    b'00001111'        ; keep only lower nibble
                        incf    FSR,F
                        iorwf    INDF,F
                        decf    FSR,F
                        decfsz    Byte_Count,F
                        goto    Shift_Lower_Right
                        movf    C1,W            ; last byte
                        andlw    b'00001111'
                        movwf    C1
                        movf    Copy_Last,W
                        iorwf    C1,F
                        return
 

Mike - K8LH

Well-Known Member
#2
Optimize for size or speed? A small savings (perhaps 250+ cycles) could be had with minor changes...

More later (gotta run)...
Code:
        radix dec
;
;  shift hi nibble to the left
;
        movlw   32              ;
        movwf   count           ;
        addlw   C1              ;
        movwf   FSR             ; FSR = address C1+32
        movf    C1,W            ; copy C[0] to C[31]
sl
        decf    FSR,F           ;
        xorwf   INDF,W          ; exchange wreg and INDF
        andlw   0xF0            ; hi nibble only
        xorwf   INDF,F          ;  "
        xorwf   INDF,W          ;  "
        decfsz  count,F         ; done? yes, skip, else
        goto    sl              ;
;
;  shift lo nibble to the right
;
        bsf     count,5         ; reset count = 32
        movf    c32,W           ; copy C[31] to C[0]
sr
        xorwf   INDF,W          ; exchange wreg and INDF
        andlw   0x0F            ; lo nibble only
        xorwf   INDF,F          ;  "
        xorwf   INDF,W          ;  "
        incf    FSR,F           ;
        decfsz  count,F         ; done? yes, skip, else
        goto    sr              ;
        return                  ;
 
Last edited:

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