few 6502 and some 65SC02 optimizations

libsrc/runtime/rsub.s

@@ -1,5 +1,6 @@
 ;
 ; Ullrich von Bassewitz, 05.08.1998
+; Christian Krueger, 11-Mar-2017, added 65SC02 optimization
 ;
 ; CC65 runtime: sub ints reversed
 ;
@@ -8,6 +9,8 @@
         .import         addysp1
         .importzp       sp, tmp1
 
+        .macpack        cpu
+
 ;
 ; AX = AX - TOS
 ;
@@ -15,12 +18,17 @@
 tosrsuba0:
         ldx     #0
 tosrsubax:
-        ldy     #0
         sec
+.if (.cpu .bitand CPU_ISET_65SC02)
+        sbc     (sp)
+        ldy     #1
+.else
+        ldy     #0
         sbc     (sp),y          ; lo byte
+        iny
+.endif
         sta     tmp1            ; save lo byte
         txa
-        iny
         sbc     (sp),y          ; hi byte
         tax
         lda     tmp1