* Improved the pop params code

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

diff --git a/device/lib/z80/mul.s b/device/lib/z80/mul.s
new file mode 100644 (file)
index 0000000..57c06a9
--- /dev/null
+++ b/device/lib/z80/mul.s
@@ -0,0 +1,78 @@
+       ;; Originally from GBDK by Pascal Felber.
+       
+       .area   _CODE
+__mulschar::   
+__muluchar::
+       push    de
+       push    bc
+       push    ix
+       ld      ix,#0
+       add     ix,sp
+
+       ld      c,8(ix)
+       ld      e,9(ix)
+       call    .mulu8
+       
+       pop     ix
+       pop     bc
+       pop     de
+       ret
+
+__mulsint::
+__muluint::
+       push    de
+       push    bc
+       push    ix
+       ld      ix,#0
+       add     ix,sp
+
+       ld      c,8(ix)
+       ld      b,9(ix)
+       ld      e,10(ix)
+       ld      d,11(ix)
+       call    .mulu16
+       
+       pop     ix
+       pop     bc
+       pop     de
+       ret
+               
+.mul8:
+.mulu8:
+       LD      B,#0x00         ; Sign extend is not necessary with mul
+       LD      D,B
+       ; Fall through
+       
+       ;; 16-bit multiplication
+       ;; 
+       ;; Entry conditions
+       ;;   BC = multiplicand
+       ;;   DE = multiplier
+       ;; 
+       ;; Exit conditions
+       ;;   DE = 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
+       JR      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
+       JR      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:
+       RET                     ; HL = result
+