auto import from //depot/cupcake/@135843
diff --git a/libc/arch-x86/string/memcmp.S b/libc/arch-x86/string/memcmp.S
new file mode 100644
index 0000000..1be189a
--- /dev/null
+++ b/libc/arch-x86/string/memcmp.S
@@ -0,0 +1,43 @@
+/* $OpenBSD: memcmp.S,v 1.4 2005/08/07 11:30:38 espie Exp $ */
+/*
+ * Written by J.T. Conklin <jtc@netbsd.org>.
+ * Public domain.
+ */
+
+#include <machine/asm.h>
+
+ENTRY(memcmp)
+ pushl %edi
+ pushl %esi
+ movl 12(%esp),%edi
+ movl 16(%esp),%esi
+ cld /* set compare direction forward */
+
+ movl 20(%esp),%ecx /* compare by words */
+ shrl $2,%ecx
+ repe
+ cmpsl
+ jne L5 /* do we match so far? */
+
+ movl 20(%esp),%ecx /* compare remainder by bytes */
+ andl $3,%ecx
+ repe
+ cmpsb
+ jne L6 /* do we match? */
+
+ xorl %eax,%eax /* we match, return zero */
+ popl %esi
+ popl %edi
+ ret
+
+L5: movl $4,%ecx /* We know that one of the next */
+ subl %ecx,%edi /* four pairs of bytes do not */
+ subl %ecx,%esi /* match. */
+ repe
+ cmpsb
+L6: movzbl -1(%edi),%eax /* Perform unsigned comparison */
+ movzbl -1(%esi),%edx
+ subl %edx,%eax
+ popl %esi
+ popl %edi
+ ret