New code for the shift functions

git-svn-id: svn://svn.cc65.org/cc65/trunk@3143 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/runtime/lshl.s

@@ -1,95 +1,44 @@
 ;
-; Ullrich von Bassewitz, 20.09.1998
+; Ullrich von Bassewitz, 2004-06-30
 ;
-; CC65 runtime: left shift support for longs
+; CC65 runtime: left shift support for long and unsigned long
+;
+; Note: The standard declares a shift count that is negative or >= the
+; bitcount of the shifted type for undefined behaviour.
+;
+; Note^2: The compiler knowns about the register/zero page usage of this
+; function, so you need to change the compiler source if you change it!
 ;
 
 
     	.export	       	tosasleax, tosshleax
-    	.import	       	addysp1
-	.importzp      	sp, sreg, ptr1, ptr2
+    	.import	       	popeax
+	.importzp      	sreg, tmp1
 
 
 tosshleax:
 tosasleax:
+        and     #$1F            ; Bring the shift count into a valid range
+        sta     tmp1            ; Save it
 
-; Get the lhs from stack into ptr1/ptr2
+        jsr     popeax          ; Get the left hand operand
 
- 	pha
- 	ldy   	#0
- 	lda   	(sp),y
- 	sta   	ptr1
-	iny
-	lda   	(sp),y
-	sta   	ptr1+1
-	iny
-	lda   	(sp),y
-	sta   	ptr2
-	iny
-	lda   	(sp),y
-	sta   	ptr2+1
-	pla
-       	jsr   	addysp1
+        ldy     tmp1            ; Get shift count
+        beq     L9              ; Bail out if shift count zero
+        stx     tmp1            ; Save byte 1
 
-; Check for shift overflow or zero shift
+; Do the actual shift. Faster solutions are possible but need a lot more code.
 
-       	tay    	       	       	; Low byte of shift count into y
-       	txa	    	       	; Get byte 2
-	ora	sreg
-       	ora    	sreg+1	       	; Check high 24 bit
-	bne	@L6            	; Shift count too large
-	cpy	#32
-	bcs    	@L6
-
-   	cpy  	#0  	       	; Shift count zero?
-   	beq  	@L5
-
-; We must shift. Shift by multiples of eight if possible
-
-   	tya
-@L1:  	cmp  	#8
-   	bcc  	@L3
-   	sbc  	#8
-       	ldx  	ptr2
-   	stx  	ptr2+1
-   	ldx  	ptr1+1
-   	stx  	ptr2
-   	ldx  	ptr1
-	stx	ptr1+1
-	ldx	#0
-	stx	ptr1
-       	beq    	@L1
-
-; Shift count is now less than eight. Do a real shift.
-
-@L3:	tay  	     	       	; Shift count to Y
-	lda    	ptr1	       	; Get one byte into A for speed
-	cpy	#0
-       	beq    	@L4a 	       	; Jump if done
-@L4:	asl	a
-   	rol    	ptr1+1
-   	rol    	ptr2
-   	rol  	ptr2+1
-   	dey
-   	bne  	@L4
-
-; Put the result in place
-
-@L4a:  	ldx	ptr2
-	stx    	sreg
-	ldx	ptr2+1
-	stx	sreg+1
-	ldx	ptr1+1
-@L5:	rts
-
-; Jump here if shift count overflow
-
-@L6:	lda    	#0
- 	sta	sreg+1
- 	sta	sreg
- 	tax
- 	rts
+L2:     asl	a
+   	rol    	tmp1
+   	rol    	sreg
+   	rol  	sreg+1
+        dey
+       	bne     L2
 
+; Shift done
 
+        ldx     tmp1
+L9:     rts