From: Mike Keitz. There is a trick method that works for 4 bits. It replaces a 2-bit number in a variable with a 4-bit mask:
incf BitP, W ;W = 0001 0010 0011 0100
btfsc BitP, 1 ;If 0 or 1, result is almost correct now.
iorwf BitP, F ;BitP = [0000] [0001] 0011 0111
incf BitP, F ;BitP = 0001 0010 0100 1000
It could be the core of an 8-bit routine thus:
; Convert 3-bit number (0-7) in INDEX to a 8-bit mask (00000001 ...
; 10000000) in BitP.
movfw INDEX
andlw b'00000011' ;Start with half of the mask.
movwf BitP
incf BitP, W ;The 4-bit converter
btfsc BitP, 1
iorwf BitP, F
incf BitP, F
btfsc INDEX, 2 ;Is it high 4 bits?
swapf BitP, F
Interested: