Initial revision

lib/i86/string/memcmp.s

@@ -0,0 +1,44 @@
+!	memcmp()					Author: Kees J. Bot
+!								27 Jan 1994
+.sect .text; .sect .rom; .sect .data; .sect .bss
+
+! int memcmp(const void *s1, const void *s2, size_t n)
+!	Compare two chunks of memory.
+!
+.sect .text
+.define _memcmp
+_memcmp:
+	cld
+	push	bp
+	mov	bp, sp
+	push	si
+	push	di
+	xor	ax, ax		! Prepare return value
+	mov	si, 4(bp)	! String s1
+	mov	di, 6(bp)	! String s2
+	mov	cx, 8(bp)	! Length
+	cmp	cx, #16
+	jb	cbyte		! Don't bother being smart with short arrays
+	mov	dx, si
+	or	dx, di
+	andb	dl, #1
+	jnz	cbyte		! Bit 0 set, use byte compare
+cword:	sar	cx, #1
+	adcb	dl, dl		! Save carry
+   repe	cmps			! Compare words
+	mov	cx, #2		! Recompare the last word
+	sub	si, cx
+	sub	di, cx
+	addb	cl, dl		! One more byte?
+cbyte:	test	cx, cx		! Set 'Z' flag if cx = 0
+last:
+   repe	cmpsb			! Look for the first differing byte
+	je	equal
+	ja	after
+	sub	ax, #2		! if (s1 < s2) ax -= 2;
+after:	inc	ax		! ax++, now it's -1 or 1
+equal:	mov	dx, si		! For bcmp() to play with
+	pop	di
+	pop	si
+	pop	bp
+	ret