diff --git a/tune/x86_64.as b/tune/x86_64.as.bak
similarity index 100%
rename from tune/x86_64.as
rename to tune/x86_64.as.bak
diff --git a/tune/x86_64.asm b/tune/x86_64.asm
new file mode 100755
index 00000000..9dd23d73
--- /dev/null
+++ b/tune/x86_64.asm
@@ -0,0 +1,46 @@
+dnl  x86 pentium time stamp counter access routine.
+
+dnl  Copyright 1999, 2000, 2003, 2004, 2005 Free Software Foundation, Inc.
+dnl
+dnl  This file is part of the GNU MP Library.
+dnl
+dnl  The GNU MP Library is free software; you can redistribute it and/or
+dnl  modify it under the terms of the GNU Lesser General Public License as
+dnl  published by the Free Software Foundation; either version 2.1 of the
+dnl  License, or (at your option) any later version.
+dnl
+dnl  The GNU MP Library is distributed in the hope that it will be useful,
+dnl  but WITHOUT ANY WARRANTY; without even the implied warranty of
+dnl  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+dnl  Lesser General Public License for more details.
+dnl
+dnl  You should have received a copy of the GNU Lesser General Public
+dnl  License along with the GNU MP Library; see the file COPYING.LIB.  If
+dnl  not, write to the Free Software Foundation, Inc., 51 Franklin Street,
+dnl  Fifth Floor, Boston, MA 02110-1301, USA.
+
+
+include(`../config.m4')
+
+
+C void speed_cyclecounter (unsigned p[2]);
+C
+C Get the pentium rdtsc cycle counter, storing the least significant word in
+C p[0] and the most significant in p[1].
+C
+C cpuid is used to serialize execution.  On big measurements this won't be
+C significant but it may help make small single measurements more accurate.
+
+PROLOGUE(speed_cyclecounter)
+
+	C rdi	p
+
+	movq	%rbx, %r10
+	xorl	%eax, %eax
+	cpuid
+	rdtsc
+	movl	%eax, (%rdi)
+	movl	%edx, 4(%rdi)
+	movq	%r10, %rbx
+	ret
+EPILOGUE()