Added separate 8x8=>16 multiplication routine as start of the multiplication

and division stuff cleanup.


git-svn-id: svn://svn.cc65.org/cc65/trunk@4431 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/runtime/Makefile

@@ -153,6 +153,7 @@ OBJS = 	add.o		\
        	mod.o  		\
        	mul.o  		\
         mul8.o          \
+        mul8x8r16.o     \
 	mulax3.o	\
 	mulax5.o	\
 	mulax6.o	\

libsrc/runtime/mul8x8r16.s

@@ -0,0 +1,35 @@
+;
+; Ullrich von Bassewitz, 2010-11-02
+;
+; CC65 runtime: 8x8 => 16 multiplication
+;
+
+       	.export		mul8x8r16, umul8x8r16
+    	.importzp	ptr1, ptr3
+
+
+;---------------------------------------------------------------------------
+; 8x8 => 16 multiplication routine.
+;
+;   lhs         rhs           result          result also in
+; -------------------------------------------------------------
+;   ptr1-lo     ptr3-lo         a/x             ptr1
+;
+
+mul8x8r16:
+umul8x8r16:
+    	lda   	#0              ; Clear byte 1
+       	ldy    	#8    	       	; Number of bits
+        lsr     ptr1            ; Get first bit of lhs into carry
+@L0:    bcc     @L1
+        clc
+        adc     ptr3
+@L1:    ror
+        ror     ptr1
+        dey
+        bne     @L0
+        tax         
+        stx     ptr1+1          ; Result in a/x and ptr1
+    	lda	ptr1  	       	; Load the result
+    	rts	   		; Done
+