| ------------------------------------------------------------------------
|  Utilities
| ------------------------------------------------------------------------

	.include "macros.inc"

|  Random number generator
| ------------------------------------------------------------------------

| Seed random number generator, using a 32 bit seed stored in d0 (s0s1s2s3 high
| to low bytes) This needn't be a pseudoroutine, but just for symmetry with the
| following routine, we'll make it one
	.text
rng_seed:
	move.b %d0, %d4
	lsr.l #8, %d0
	move.b %d0, %d5
	lsr.l #8, %d0
	move.b %d0, %d6
	lsr.l #8, %d0
	move.b %d0, %d7
	pseudo_ret

| Reverse of seed: it will collect the seed from registers d4-d7 to d0	
rng_unseed:
	move.b	%d7, %d0
	lsl.l	#8, %d0
	move.b	%d6, %d0
	lsl.l	#8, %d0
	move.b	%d5, %d0
	lsl.l	#8, %d0
	move.b	%d4, %d0
	lsl.l	#8, %d0
	pseudo_ret
	
| Calculate next random number, it will be stored in the low byte of d7
rng_calc_next:
	add.l #1, %d4
	eor.b %d7, %d5
	eor.b %d4, %d5
	add.b %d5, %d6
	
	lsl.w #8, %d4	| Hack	- shift d4 to the left, so we can use its 8 LSB for storing the intermediate value
	move.b %d6, %d4	| 		- Tmp store d6
	lsr.b #1, %d4	|		- This will produce d6>>1 in the LSB
	
	add.b %d4, %d7	| Yup! I remebered it!
	
	lsr.w #8, %d4	| Hack	- Revert d4 to what it was before
	
	eor.b %d5, %d7
	pseudo_ret

| Function exposed to C - 1 longword argument
	.global rng_next
rng_next:
	link %fp, #0
	movem %d2-%d7/%a2-%a5, -(%sp)
	move.l	8(%fp), %d0
	pseudo_call rng_seed
	pseudo_call rng_calc_next
	pseudo_call rng_unseed
	movem (%sp)+, %d2-%d7/%a2-%a5
	unlk %fp
	rts