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 =   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
+Still, a simple table lookup or 8-bits is less instruction cycles and doesn't need a temp register. And it can do a little math too (set bit 7-WREG instead of bit WREG) GET_BIT ADDWF PCL,F RETLW B'00000001' RETLW B'00000010' RETLW B'00000100' RETLW B'00001000' RETLW B'00010000' RETLW B'00100000' RETLW B'01000000' RETLW B'10000000' GET_BIT2 ADDWF PCL,F RETLW B'10000000' RETLW B'01000000' RETLW B'00100000' RETLW B'00010000' RETLW B'00001000' RETLW B'00000100' RETLW B'00000010' RETLW B'00000001'
|file: /Techref/microchip/math/bit/mask.htm, 2KB, , updated: 2008/10/8 04:23, local time: 2020/11/26 16:42,
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<A HREF="http://www.sxlist.com/techref/microchip/math/bit/mask.htm"> PIC Microcontoller Bit Math Method Converting a 3-bit number to a 8-bit mask</A>
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