Optimize stpcpy's size and speed

colinleroy · Sep 4, 2024 · f658cd7 · f658cd7
1 parent 622793e
commit f658cd7
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Showing 3 changed files with 23 additions and 9 deletions.
diff --git a/libsrc/common/stpcpy.c b/libsrc/common/stpcpy.c
diff --git a/libsrc/common/stpcpy.s b/libsrc/common/stpcpy.s
@@ -0,0 +1,22 @@
+;
+; Colin Leroy-Mira, 4 Sept. 2024
+;
+; char* stpcpy (char* dest, const char* src);
+;
+
+        .export         _stpcpy
+        .import         _strcpy
+
+        .importzp       tmp1, ptr2
+
+_stpcpy:
+        jsr     _strcpy
+
+        ldx     ptr2+1        ; Load dest pointer's last high byte
+        sty     tmp1          ; Store low byte's offset
+
+        clc
+        adc     tmp1          ; Add to low byte value
+        bcc     :+
+        inx
+:       rts
diff --git a/libsrc/common/strcpy.s b/libsrc/common/strcpy.s
@@ -25,6 +25,5 @@ L1:     lda     (ptr1),y
         inc     ptr2+1
         bne     L1
 
-L9:     lda     ptr2            ; X still contains high byte
+L9:     lda     ptr2            ; X still contains dest's original high byte
         rts
-