2 files changed, 210 insertions, 0 deletions
diff --git a/common/copy2.asm b/common/copy2.asm
new file mode 100644
index 000000000..bdfbe9fdf
--- /dev/null
+++ b/common/copy2.asm
@@ -0,0 +1,134 @@
+CopyBytes: ; 0x3026
+; copy bc bytes from hl to de
+	inc b  ; we bail the moment b hits 0, so include the last run
+	inc c  ; same thing; include last byte
+	jr .HandleLoop
+.CopyByte
+	ld a, [hli]
+	ld [de], a
+	inc de
+.HandleLoop
+	dec c
+	jr nz, .CopyByte
+	dec b
+	jr nz, .CopyByte
+	ret
+
+SwapBytes: ; 0x3034
+; swap bc bytes between hl and de
+.Loop
+	; stash [hl] away on the stack
+	ld a, [hl]
+	push af
+
+	; copy a byte from [de] to [hl]
+	ld a, [de]
+	ld [hli], a
+
+	; retrieve the previous value of [hl]; put it in [de]
+	pop af
+	ld [de], a
+	inc de
+
+	; handle loop stuff
+	dec bc
+	ld a, b
+	or c
+	jr nz, .Loop
+	ret
+
+ByteFill: ; 0x3041
+; fill bc bytes with the value of a, starting at hl
+	inc b  ; we bail the moment b hits 0, so include the last run
+	inc c  ; same thing; include last byte
+	jr .HandleLoop
+.PutByte
+	ld [hli], a
+.HandleLoop
+	dec c
+	jr nz, .PutByte
+	dec b
+	jr nz, .PutByte
+	ret
+
+GetFarByte: ; 0x304d
+; retrieve a single byte from a:hl, and return it in a.
+	; bankswitch to new bank
+	ld [hBuffer], a
+	ld a, [hROMBank]
+	push af
+	ld a, [hBuffer]
+	rst Bankswitch
+
+	; get byte from new bank
+	ld a, [hl]
+	ld [hBuffer], a
+
+	; bankswitch to previous bank
+	pop af
+	rst Bankswitch
+
+	; return retrieved value in a
+	ld a, [hBuffer]
+	ret
+
+GetFarHalfword: ; 0x305d
+; retrieve a halfword from a:hl, and return it in hl.
+	; bankswitch to new bank
+	ld [hBuffer], a
+	ld a, [hROMBank]
+	push af
+	ld a, [hBuffer]
+	rst Bankswitch
+
+	; get halfword from new bank, put it in hl
+	ld a, [hli]
+	ld h, [hl]
+	ld l, a
+
+	; bankswitch to previous bank and return
+	pop af
+	rst Bankswitch
+	ret
+; 0x306b
+
+FarCopyWRAM: ; 306b
+	ld [hBuffer], a
+	ld a, [rSVBK]
+	push af
+	ld a, [hBuffer]
+	ld [rSVBK], a
+	call CopyBytes
+	pop af
+	ld [rSVBK], a
+	ret
+; 307b
+
+GetFarWRAMByte: ; 307b
+	ld [hBuffer], a
+	ld a, [rSVBK]
+	push af
+	ld a, [hBuffer]
+	ld [rSVBK], a
+	ld a, [hl]
+	ld [hBuffer], a
+	pop af
+	ld [rSVBK], a
+	ld a, [hBuffer]
+	ret
+; 308d
+
+GetFarWRAMWord: ; 308d
+	ld [hBuffer], a
+	ld a, [rSVBK]
+	push af
+	ld a, [hBuffer]
+	ld [rSVBK], a
+	ld a, [hli]
+	ld h, [hl]
+	ld l, a
+	pop af
+	ld [rSVBK], a
+	ret
+; 309d
+
diff --git a/common/math.asm b/common/math.asm
new file mode 100644
index 000000000..87a00c412
--- /dev/null
+++ b/common/math.asm
@@ -0,0 +1,76 @@
+SimpleMultiply: ; 3105
+; Return a * c.
+	and a
+	ret z
+
+	push bc
+	ld b, a
+	xor a
+.loop
+	add c
+	dec b
+	jr nz, .loop
+	pop bc
+	ret
+; 3110
+
+
+SimpleDivide: ; 3110
+; Divide a by c. Return quotient b and remainder a.
+	ld b, 0
+.loop
+	inc b
+	sub c
+	jr nc, .loop
+	dec b
+	add c
+	ret
+; 3119
+
+
+Multiply: ; 3119
+; Multiply hMultiplicand (3 bytes) by hMultiplier. Result in hProduct.
+; All values are big endian.
+	push hl
+	push bc
+
+	callab _Multiply
+
+	pop bc
+	pop hl
+	ret
+; 3124
+
+
+Divide: ; 3124
+; Divide hDividend length b (max 4 bytes) by hDivisor. Result in hQuotient.
+; All values are big endian.
+	push hl
+	push de
+	push bc
+	ld a, [hROMBank]
+	push af
+	ld a, BANK(_Divide)
+	rst Bankswitch
+
+	call _Divide
+
+	pop af
+	rst Bankswitch
+	pop bc
+	pop de
+	pop hl
+	ret
+; 3136
+
+
+SubtractSigned: ; 3136
+; Return a - b, sign in carry.
+	sub b
+	ret nc
+	cpl
+	add 1
+	scf
+	ret
+; 313d
+