1 files changed, 66 insertions, 0 deletions
diff --git a/src/home/random.asm b/src/home/random.asm
new file mode 100644
index 0000000..d731b12
--- /dev/null
+++ b/src/home/random.asm
@@ -0,0 +1,66 @@
+; returns h * l in hl
+HtimesL:
+	push de
+	ld a, h
+	ld e, l
+	ld d, $0
+	ld l, d
+	ld h, d
+	jr .asm_887
+.asm_882
+	add hl, de
+.asm_883
+	sla e
+	rl d
+.asm_887
+	srl a
+	jr c, .asm_882
+	jr nz, .asm_883
+	pop de
+	ret
+
+; return a random number between 0 and a (exclusive) in a
+Random:
+	push hl
+	ld h, a
+	call UpdateRNGSources
+	ld l, a
+	call HtimesL
+	ld a, h
+	pop hl
+	ret
+
+; get the next random numbers of the wRNG1 and wRNG2 sequences
+UpdateRNGSources:
+	push hl
+	push de
+	ld hl, wRNG1
+	ld a, [hli]
+	ld d, [hl] ; wRNG2
+	inc hl
+	ld e, a
+	ld a, d
+	rlca
+	rlca
+	xor e
+	rra
+	push af
+	ld a, d
+	xor e
+	ld d, a
+	ld a, [hl] ; wRNGCounter
+	xor e
+	ld e, a
+	pop af
+	rl e
+	rl d
+	ld a, d
+	xor e
+	inc [hl] ; wRNGCounter
+	dec hl
+	ld [hl], d ; wRNG2
+	dec hl
+	ld [hl], e ; wRNG1
+	pop de
+	pop hl
+	ret