Move cpuid facility to separate package

internal/cpuid/cpuid_x86.go

@@ -28,7 +28,7 @@
 
 // +build 386 amd64 amd64p32
 
-package tz
+package cpuid
 
 const (
 	bitOSXSAVE = 1 << 27
@@ -36,14 +36,19 @@ const (
 	bitAVX2    = 1 << 5
 )
 
-func setFeatures() {
+var (
+	hasAVX  bool
+	hasAVX2 bool
+)
+
+func init() {
 	maxID, _, _, _ := cpuid(0, 0)
 	if maxID < 1 {
 		return
 	}
 
 	_, _, ecx1, _ := cpuid(1, 0)
-	hasOSXSAVE = isSet(ecx1, bitOSXSAVE)
+	hasOSXSAVE := isSet(ecx1, bitOSXSAVE)
 
 	osSupportsAVX := false
 	if hasOSXSAVE {
@@ -61,6 +66,9 @@ func setFeatures() {
 	hasAVX2 = isSet(ebx7, bitAVX2) && osSupportsAVX
 }
 
+func HasAVX() bool  { return hasAVX }
+func HasAVX2() bool { return hasAVX2 }
+
 func isSet(hwc uint32, value uint32) bool {
 	return hwc&value != 0
 }

tz/hash.go

@@ -6,6 +6,8 @@ package tz
 import (
 	"errors"
 	"hash"
+
+	"github.com/nspcc-dev/tzhash/internal/cpuid"
 )
 
 type Implementation int
@@ -22,9 +24,8 @@ const (
 )
 
 var (
-	hasAVX     bool
-	hasAVX2    bool
-	hasOSXSAVE bool
+	hasAVX  = cpuid.HasAVX()
+	hasAVX2 = cpuid.HasAVX2()
 )
 
 func (impl Implementation) String() string {

tz/sl2.go

@@ -17,8 +17,6 @@ var id = sl2{
 var mul func(a, b, c *sl2, x *[4]gf127.GF127)
 
 func init() {
-	setFeatures()
-
 	if hasAVX {
 		mul = mulSL2AVX
 	} else {