Added further optimizations and unit tests.

libsrc/common/strncat.s

@@ -1,5 +1,6 @@
 ;
 ; Ullrich von Bassewitz, 31.05.1998
+; Christian Krueger: 12-Aug-2013, minor optimizations
 ;
 ; char* strncat (char* dest, const char* src, size_t n);
 ;
@@ -9,64 +10,65 @@
         .importzp       ptr1, ptr2, ptr3, tmp1, tmp2
 
 _strncat:
-        eor     #$FF            ; one's complement to count upwards
-        sta     tmp1
-        txa
-        eor     #$FF
-        sta     tmp2
-        jsr     popax           ; get src
-        sta     ptr1
-        stx     ptr1+1
-        jsr     popax           ; get dest
-        sta     ptr2
-        stx     ptr2+1
-        sta     ptr3            ; remember for function return
-        stx     ptr3+1
-        ldy     #0
+    eor #$FF        ; one's complement to count upwards
+    sta tmp1
+    txa
+    eor #$FF
+    sta tmp2
+    
+    jsr popax       ; get src
+    sta ptr1
+    stx ptr1+1
+
+    jsr popax       ; get dest
+    sta ptr3        ; remember for function return
+    stx ptr3+1          
+    stx ptr2+1
+    tay             ; low byte as offset in Y
+.if (.cpu .bitand ::CPU_ISET_65SC02)
+    stz ptr2
+.else
+    ldx #0
+    stx ptr2        ; destination on page boundary
+.endif
 
 ; find end of dest
 
-L1:     lda     (ptr2),y
-        beq     L2
-        iny
-        bne     L1
-        inc     ptr2+1
-        bne     L1
+L1: lda (ptr2),y
+    beq L2
+    iny
+    bne L1
+    inc ptr2+1
+    bne L1
 
-; end found, get offset in y into pointer
-
-L2:     tya
-        clc
-        adc     ptr2
-        sta     ptr2
-        bcc     L3
-        inc     ptr2+1
+; end found, apply offset to dest ptr and reset y
+L2: sty ptr2
 
 ; copy src. We've put the ones complement of the count into the counter, so
 ; we'll increment the counter on top of the loop
 
-L3:     ldy     #0
-        ldx     tmp1            ; low counter byte
+L3: ldy #0
+    ldx tmp1        ; low counter byte
 
-L4:     inx
-        bne     L5
-        inc     tmp2
-        beq     L6              ; jump if done
-L5:     lda     (ptr1),y
-        sta     (ptr2),y
-        beq     L7
-        iny
-        bne     L4
-        inc     ptr1+1
-        inc     ptr2+1
-        bne     L4
+L4: inx
+    bne L5
+    inc tmp2
+    beq L6          ; jump if done
+L5: lda (ptr1),y
+    sta (ptr2),y
+    beq L7
+    iny
+    bne L4
+    inc ptr1+1
+    inc ptr2+1
+    bne L4
 
 ; done, set the trailing zero and return pointer to dest
 
-L6:     lda     #0
-        sta     (ptr2),y
-L7:     lda     ptr3
-        ldx     ptr3+1
-        rts
+L6: lda #0
+    sta (ptr2),y
+L7: lda ptr3
+    ldx ptr3+1
+    rts