Minor improvements, code cleanup and license clarification

[fw/sdcc] / device / lib / z80 / mul.s

diff --git a/device/lib/z80/mul.s b/device/lib/z80/mul.s
index fa3fb63ebfcebfa43eb9e0686ef39e767a8daa55..61ff5cf34179e99e6ab25d8ac8c2726725d46555 100644 (file)
--- a/device/lib/z80/mul.s
+++ b/device/lib/z80/mul.s
@@ -1,47 +1,9 @@
-       ;; Originally from GBDK by Pascal Felber.
-       
-       .area   _CODE
+        .area   _CODE
 
-__mulschar_rr_s::
+__mulint_rrx_s::
         ld      hl,#2
         add     hl,sp
 
-        ld      e,(hl)
-        inc     hl
-        ld      l,(hl)                
-
-        ;; Fall through
-__mulschar_rr_hds::
-        ;; Need to sign extend before going in.
-        ld      c,l
-        
-        ld      a,l
-        rla
-        sbc     a,a
-        ld      b,a
-
-        ld      a,e
-        rla
-        sbc     a,a
-        ld      d,a
-
-        jp      .mul16
-
-__muluchar_rr_s::
-        ld      hl,#2
-        add     hl,sp
-
-        ld      e,(hl)
-        inc     hl
-        ld      c,(hl)                
-
-        jp      .mulu16
-        
-__mulsint_rr_s::
-__muluint_rr_s::
-        ld      hl,#2
-        add     hl,sp
-        
         ld      e,(hl)
         inc     hl
         ld      d,(hl)
@@ -52,46 +14,45 @@ __muluint_rr_s::
         ld      l,a
 
         ;; Fall through
-        
-__muluchar_rr_hds::
-__mulsint_rr_hds::
-__muluint_rr_hds::
+
+__muluchar_rrx_hds::
+__mulint_rrx_hds::
        ;; Parameters:
-       ;;      HL, DE (left, right irrelivent)
+       ;;      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
-       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