;       swapbits: PeANUt assembler program (procedure) for COMP2300 Lab Exercise 5


global SwapBits			; export SwapBits;
				; void SwapBits( char *x ); 	
				;   const short int
LBtMsk: data	%0000 1111	;     LBtMsk = 0x0f,       /*mask for bits 0-3*/
HBtMsk: data	%1111 0000	;     HBtMsk = 0xf0,       /*mask for bits 4-7*/
LBtShft:data	%0001 0000	;     LBtShft = 16; /* shift low <-> high bits*/
				;   char
xtmp:	block	1		;     xtmp, 	  /* implement via direct mode*/
				;     xL,		/* implement via stack*/
				;     xH;		/* implement via stack*/
SwapBits:			;   
				; 	
				;     xtmp = *x;
				;
				;
				;
 				;     xL = xtmp & LBtMsk; 
				;
				;
 				;     xH = (xtmp & HBtMsk) / LBtShft; 
				;
				;
				;
				;     xtmp = xL * LBtShft;
				;
				;
				;     *x = xH | xtmp;
				;
				;
				;
				;
				;   } /*SwapBits()*/	 
	ret			;