X-Git-Url: https://git.gag.com/?a=blobdiff_plain;f=device%2Flib%2Fz80%2Fmul.s;h=61ff5cf34179e99e6ab25d8ac8c2726725d46555;hb=e56ff7ea8ea1bffdcf4fee43ec8a125453a6ad8d;hp=9c33ac30aa4054d95e9c6db7958b1a43198630fb;hpb=1dc186b793ade0a904f642c0cb497c418009cd34;p=fw%2Fsdcc

diff --git a/device/lib/z80/mul.s b/device/lib/z80/mul.s
index 9c33ac30..61ff5cf3 100644
--- a/device/lib/z80/mul.s
+++ b/device/lib/z80/mul.s
@@ -1,66 +1,58 @@
-	;; Originally from GBDK by Pascal Felber.
-	
-	.area	_CODE
-	
-__mulschar::
-        ;; Need to sign extend before going in.
-        push    bc
-        ld      c,l
-        
-        ld      a,l
-        rla
-        sbc     a,a
-        ld      b,a
+        .area   _CODE
 
-        ld      a,e
-        rla
-        sbc     a,a
-        ld      d,a
+__mulint_rrx_s::
+        ld      hl,#2
+        add     hl,sp
 
-        jp      .mul16
+        ld      e,(hl)
+        inc     hl
+        ld      d,(hl)
+        inc     hl
+        ld      a,(hl)
+        inc     hl
+        ld      h,(hl)
+        ld      l,a
 
-__muluchar::
-__mulsint::
-__muluint::
+        ;; Fall through
+
+__muluchar_rrx_hds::
+__mulint_rrx_hds::
 	;; Parameters:
-	;;	HL, DE (left, right irrelivent)
-	;; Must preserve BC
-	push	bc
+	;;	hl, de (left, right irrelevant)
 	ld	b,h
 	ld	c,l
-	
+
 	;; 16-bit multiplication
-	;; 
+	;;
 	;; Entry conditions
-	;;   BC = multiplicand
-	;;   DE = multiplier
-	;; 
+	;; bc = multiplicand
+	;; de = multiplier
+	;;
 	;; Exit conditions
-	;;   DE = less significant word of product
+	;; hl = less significant word of product
 	;;
 	;; Register used: AF,BC,DE,HL
-.mul16:
-.mulu16:
-	LD	HL,#0x00	; Product = 0
-	LD	A,#15		; Count = bit length - 1
-	;; Shift-and-add algorithm
-	;; If MSB of multiplier is 1, add multiplicand to partial product
-	;; Shift partial product, multiplier left 1 bit
-.mlp:
-	SLA	E		; Shift multiplier left 1 bit
-	RL	D
-	jp	NC,.mlp1	; Jump if MSB of multiplier = 0
-	ADD	HL,BC		; Add multiplicand to partial product
-.mlp1:
-	ADD	HL,HL		; Shift partial product left
-	DEC	A
-	jp	NZ,.mlp		; Continue until count = 0
-	;; Add multiplicand one last time if MSB of multiplier is 1
-	BIT	7,D		; Get MSB of multiplier
-	JR	Z,.mend		; Exit if MSB of multiplier is 0
-	ADD	HL,BC		; Add multiplicand to product
-.mend:
-				; HL = result
-	pop	bc
-	ret
+__mul16::
+	xor	a,a
+	ld	l,a
+	or	a,b
+	ld	b,#16
+
+        ;; Optimise for the case when this side has 8 bits of data or
+        ;; less.  This is often the case with support address calls.
+        jr      NZ,2$
+        ld      b,#8
+        ld      a,c
+1$:
+        ;; Taken from z88dk, which originally borrowed from the
+        ;; Spectrum rom.
+        add     hl,hl
+2$:
+        rl      c
+        rla                     ;DLE 27/11/98
+        jr      NC,3$
+        add     hl,de
+3$:
+        djnz    1$
+        ret