Shift by 4 bits at a time

Code:

• mark_jeronimus-gmail- shares this code:

  This will shift an array of values to the right by 4 bits, filling the leftmost nibble with zeros.
  
  Example:
  Before:
    Temp3 = 12h
    Temp2 = 34h
    Temp1 = 56h
    Temp0 = 78h
  After:
    Temp3 = 01h
    Temp2 = 23h
    Temp1 = 45h
    Temp0 = 67h
  
  It can be extended to any length and shifting to the left works on the same principle.
  
  	SWAPF	TEMP0,W
  	ANDLW	0x0F
  	MOVWF	TEMP0
  
  	SWAPF	TEMP1,W
  	MOVWF	TEMP1
  	ANDLW	0xF0
  	IORWF	TEMP0,F
  	MOVLW	0x0F
  	ANDWF	TEMP1,F	
  
  	SWAPF	TEMP2,W
  	MOVWF	TEMP2
  	ANDLW	0xF0
  	IORWF	TEMP1,F
  	MOVLW	0x0F
  	ANDWF	TEMP2,F	
  
  	SWAPF	TEMP3,W
  	MOVWF	TEMP3
  	ANDLW	0xF0
  	IORWF	TEMP2,F
  	MOVLW	0x0F
  	ANDWF	TEMP2,F	
  
  	...

Alex Davies of Ace Electronics Engineering Says:

You can save 1 word per byte on the above by using XOR swaps with W as a carry register. ie, to shift to the left by a nibble:

SWAPF TEMP0, W
MOVWF TEMP0
ANDLW 0x0F
XORWF TEMP0, F

SWAPF TEMP1, F
XORWF TEMP1, F
XORWF TEMP1, W
ANDLW 0x0F
XORWF TEMP1, F

SWAPF TEMP2, F
XORWF TEMP2, F
XORWF TEMP2, W
ANDLW 0x0F
XORWF TEMP2, F

...

(untested)