/*
 * Instruction word format:
 * 	|31         <- Bit position ->         0|
 * 	|INS7|INS6|INS5|INS4|INS3|INS2|INS1|INS0|
 *      -----------------------------------------
 * 	|INS7|INS6|INS5|INS4|INS3|INS2|INS1|0000| INS0 = NOP
 * 	|INS7|INS6|INS5|INS4|INS3|INS2|INS1|0100| INS0 = PLUS
 * 	|INS7|INS6|INS5|INS4|INS3|INS2|INS1|1000| INS0 = DUP
 * 	|INS7|INS6|INS5|INS4|INS3|INS2|INS1|1100| INS0 = SWAP
 *	|LLLL|LLLL|LLLL|LLLL|LLLL|LLLL|LLLL|LL01| LITERAL (30 bit data)
 *	|OOOO|OOOO|OOOO|OOOO|OOOO|OOOO|OOOO|OO10| QBRANCH (32 bit offset)
 *	|AAAA|AAAA|AAAA|AAAA|AAAA|AAAA|AAAA|AA11| CALL (32 bit address)
 *
 *	The destination of QBRANCH and CALL is a word (4 byte) aligned address.
 *
 *	Literals > 3FFFFFFF can be pushed on the stack in multiple steps.
 *	00000000 - 3FFFFFFF  LITERAL (n)
 *	40000000 - 7FFFFFFE  LITERAL (n-3FFFFFFF) LITERAL 3FFFFFFF PLUS
 *	7FFFFFFF - BFFFFFFF  LITERAL (n-40000000) 
 *	C0000000 - FFFFFFFF  LITERAL (~n) NOT
 */

#define NOOP	0x0	/* ( -- )		No operation */
#define AND	0x1	/* ( n1 n2 -- n3 )	n3 = n1 & n2 */
#define XOR	0x2	/* ( n1 n2 -- n3 )	n3 = n1 ^ n2 */
#define NOT	0x3	/* ( n1 -- n2 )		n2 = ~n1 */
#define PLUS	0x4	/* ( n1 n2 -- n3 )	n3 = n1 + n2 */
#define STORE	0x5	/* ( x a -- )		Write word x to address a */
#define FETCH	0x6	/* ( a -- x )		Read word x from address a */
#define EXIT	0x7	/* ( R: a -- )		Return from a CALL */
#define DUP	0x8	/* ( x -- x x )		Duplicate top cell */
#define DROP	0x9	/* ( x -- )		Remove top cell */
#define TOR	0xa	/* ( x -- ) ( R: -- x )	Move cell to return stack */
#define RFROM	0xb	/* ( -- x ) ( R: x -- )	Move cell from return stack */
#define SWAP	0xc	/* ( x1 x2 -- x2 x1 )	Exchange top two cells */
#define RSHIFT	0xd	/* ( n1 -- n2 )		n2 = n1 >> 1 (arithmetic) */
#define LRSHIFT	0xe	/* ( n1 -- n2 )		n2 = n1 >> 1 (logical) */
#define HALT	0xf	/* ( -- )		Halt execution */

/* INS0 restricted operations */
#define LITERAL	0x1	/* ( -- x ) */
#define QBRANCH	0x2	/* ( f -- ) */
#define CALL	0x3	/* ( R: -- a ) */

/* Cell size in bytes */
#define CELL_SIZE 4

/* Instruction pipe size in instructions - must be >= 2 */
#define PIPE_SIZE 8

/* Stack size in cells must be a power of 2 (default = 16) */
#define DSTACK_CELLS	(1 << 4)
#define RSTACK_CELLS	(1 << 4)

#define DSTACK_MASK	(DSTACK_CELLS - 1)
#define RSTACK_MASK	(RSTACK_CELLS - 1)