Fixed an error and improved the code

git-svn-id: svn://svn.cc65.org/cc65/trunk@3317 b7a2c559-68d2-44c3-8de9-860c34a00d81

diff --git a/libsrc/common/_swap.s b/libsrc/common/_swap.s
index 7f3f98fa0a2f2e2a754ba716ab0e9bc5559ef82f..7f0b59e940d9c171119cf0bb7cd2a9b3187d6b2e 100644 (file)
--- a/libsrc/common/_swap.s
+++ b/libsrc/common/_swap.s
@@ -1,62 +1,55 @@
 ;
-; Ullrich von Bassewitz, 09.12.1998
+; Ullrich von Bassewitz, 1998-12-09, 2004-11-30
 ;
 ; void __fastcall__ _swap (void* p, void* q, size_t size);
 ;
 
-       .export         __swap
-       .import         popax
-       .importzp       ptr1, ptr2, ptr3
+       .export         __swap
+       .import         popax
+       .importzp       ptr1, ptr2, ptr3
 
 
-__swap:        sta     ptr3            ; Save size
-       stx     ptr3+1
+__swap:        eor     #$FF
+        sta    ptr3
+        txa
+        eor     #$FF
+               sta     ptr3+1          ; Save -(size+1) into ptr3
 
-       jsr     popax           ; Get q
-       sta     ptr2
-       stx     ptr2+1
+       jsr     popax           ; Get q
+       sta     ptr2
+       stx     ptr2+1
 
-       jsr     popax           ; Get p
-       sta     ptr1
-       stx     ptr1+1
+       jsr     popax           ; Get p
+       sta     ptr1
+       stx     ptr1+1
 
 ; Prepare for swap
 
-       ldy     #$00
+       ldy     #$00
 
-; Swap 256 byte blocks
+; Swap loop
 
-       ldx     ptr3+1
-       beq     @L2
+@L1:    inc     ptr3            ; Bump counter low byte
+        beq     @L3             ; Branch on overflow
 
-@L1:   lda     (ptr1),y
-       tax
-       lda     (ptr2),y
-       sta     (ptr1),y
-       txa
-       sta     (ptr2),y
-       iny
-       bne     @L1
-       dec     ptr3+1
-       bne     @L1
+@L2:    lda    (ptr1),y
+       tax
+       lda     (ptr2),y
+       sta     (ptr1),y
+       txa
+       sta     (ptr2),y
+       iny
+       bne     @L1
+        inc     ptr1+1
+        inc     ptr2+1
+        bne     @L1             ; Branch always (hopefully)
 
-; Swap remaining bytes (Y is zero)
+; Bump the high counter byte
 
-@L2:   ldx     ptr3
-       beq     @L9
-
-@L3:           lda     (ptr1),y
-       tax
-       lda     (ptr2),y
-       sta     (ptr1),y
-       txa
-       sta     (ptr2),y
-       iny
-       dec     ptr3
-       bne     @L3
+@L3:    inc     ptr3+1
+        bne     @L2
 
 ; Done
 
-@L9:   rts
-
+        rts