Revert "libc x86: Remove strcat.S"
This reverts commit 4fe461b3a67148a2f557605e10a34deff9c8773a
Change-Id: Ibeb76e24f054abd7c96ad6899366c2f9bfc2a5ad
diff --git a/libc/arch-x86/string/strcat.S b/libc/arch-x86/string/strcat.S
new file mode 100644
index 0000000..c75f38a
--- /dev/null
+++ b/libc/arch-x86/string/strcat.S
@@ -0,0 +1,74 @@
+/* $OpenBSD: strcat.S,v 1.8 2005/08/07 11:30:38 espie Exp $ */
+/*
+ * Written by J.T. Conklin <jtc@netbsd.org>.
+ * Public domain.
+ */
+
+#include <machine/asm.h>
+
+#if defined(APIWARN)
+#APP
+ .section .gnu.warning.strcat
+ .ascii "warning: strcat() is almost always misused, please use strlcat()"
+#NO_APP
+#endif
+
+/*
+ * NOTE: I've unrolled the loop eight times: large enough to make a
+ * significant difference, and small enough not to totally trash the
+ * cache.
+ */
+
+ENTRY(strcat)
+ pushl %edi /* save edi */
+ movl 8(%esp),%edi /* dst address */
+ movl 12(%esp),%edx /* src address */
+ pushl %edi /* push destination address */
+
+ cld /* set search forward */
+ xorl %eax,%eax /* set search for null terminator */
+ movl $-1,%ecx /* set search for lots of characters */
+ repne /* search! */
+ scasb
+
+ leal -1(%edi),%ecx /* correct dst address */
+
+ .align 2,0x90
+L1: movb (%edx),%al /* unroll loop, but not too much */
+ movb %al,(%ecx)
+ testb %al,%al
+ jz L2
+ movb 1(%edx),%al
+ movb %al,1(%ecx)
+ testb %al,%al
+ jz L2
+ movb 2(%edx),%al
+ movb %al,2(%ecx)
+ testb %al,%al
+ jz L2
+ movb 3(%edx),%al
+ movb %al,3(%ecx)
+ testb %al,%al
+ jz L2
+ movb 4(%edx),%al
+ movb %al,4(%ecx)
+ testb %al,%al
+ jz L2
+ movb 5(%edx),%al
+ movb %al,5(%ecx)
+ testb %al,%al
+ jz L2
+ movb 6(%edx),%al
+ movb %al,6(%ecx)
+ testb %al,%al
+ jz L2
+ movb 7(%edx),%al
+ movb %al,7(%ecx)
+ addl $8,%edx
+ addl $8,%ecx
+ testb %al,%al
+ jnz L1
+L2: popl %eax /* pop destination address */
+ popl %edi /* restore edi */
+ ret
+END(strcat)
