--- /dev/null
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build amd64,!appengine,!gccgo
+
+#include "textflag.h"
+
+// func havePOPCNT() bool
+TEXT ·havePOPCNT(SB),4,$0
+ MOVQ $1, AX
+ CPUID
+ SHRQ $23, CX
+ ANDQ $1, CX
+ MOVB CX, ret+0(FP)
+ RET
+
+// func popcnt(word) int
+TEXT ·popcnt(SB),NOSPLIT,$0-8
+ XORQ AX, AX
+ MOVQ x+0(FP), SI
+ // POPCNT (SI), AX is not recognized by Go assembler,
+ // so we assemble it ourselves.
+ BYTE $0xf3
+ BYTE $0x48
+ BYTE $0x0f
+ BYTE $0xb8
+ BYTE $0xc6
+ MOVQ AX, ret+8(FP)
+ RET