Added the capability to search for the terminating zero of the given string.

Don't know what the standard says about it, but the feature seems reasonable
and other compilers handle it this way.


git-svn-id: svn://svn.cc65.org/cc65/trunk@42 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/common/strchr.s

@@ -4,9 +4,9 @@
 ; const char* strchr (const char* s, int c);
 ;
 
-	.export		_strchr
-	.import		popax
-	.importzp	ptr1, tmp1
+      	.export		_strchr
+      	.import		popax
+      	.importzp	ptr1, tmp1
 
 _strchr:
        	sta	tmp1		; Save c
@@ -15,27 +15,34 @@ _strchr:
        	stx	ptr1+1
        	ldy	#0
 
-scloop:	lda	(ptr1),y	; get next char
-       	beq	strz  		; jump if end of string
-       	cmp	tmp1  		; found?
-       	beq	strf  		; jump if yes
+Loop: 	lda	(ptr1),y	; Get next char
+	beq	EOS		; Jump on end of string
+      	cmp	tmp1		; Found?
+      	beq	Found		; Jump if yes
        	iny
-       	bne	scloop
+       	bne	Loop
        	inc	ptr1+1
-       	bne	scloop		; jump always
+       	bne	Loop		; Branch always
 
-; found, calculate pointer to c
+; End of string. Check if we're searching for the terminating zero
 
-strf:  	ldx	ptr1+1		; get high byte of pointer
-       	tya			; low byte offset
+EOS:	lda	tmp1		; Get the char we're searching for
+      	bne	NotFound	; Jump if not searching for terminator
+
+; Found. Calculate pointer to c.
+
+Found:	ldx	ptr1+1		; Load high byte of pointer
+	tya			; Low byte offset	   
        	clc
        	adc	ptr1
-       	bcc	str1
+       	bcc	Found1
        	inx
-str1:  	rts
+Found1:	rts
 
-; not found, return zero
+; Not found, return NULL
 
-strz:	tax			; return 0
+NotFound:
+	lda	#0
+	tax
 	rts