SX Microcontroller Bit Math Method

Rotate the nibbles within a byte.

From Dmitry Kiryashov [zews at AHA.RU]

a) abcd.efgh -> bcda.fghe

	mov	W, <<X
	rl	X		;bcdefgha

	mov	W, <>X		;...a...e
	xor	W, X
	and	W, #$11		;...<a^e>...<e^a>
	xor	X, W		;bcdafghe

b) abcd.efgh -> dabc.hefg

	mov	W, >>X
	rr	X		;habcdefg

	mov	W, <>X		;d...h...
	xor	W, X
	and	W, #$88		;<d^h>...<h^d>...
	xor	X, W		;dabchefg

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