hash/maphash: sync wyhash with runtime implementation

Fixes #69940

Change-Id: I40535d2647f9456d2196241bf7414b1e92b53c2c
Reviewed-on: https://go-review.googlesource.com/c/go/+/621756
Reviewed-by: Keith Randall <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: cuonglm

src/hash/maphash/maphash_purego.go

@@ -13,6 +13,14 @@ import (
 	"reflect"
 )
 
+var hashkey [4]uint64
+
+func init() {
+	for i := range hashkey {
+		hashkey[i] = randUint64()
+	}
+}
+
 func rthash(buf []byte, seed uint64) uint64 {
 	if len(buf) == 0 {
 		return seed
@@ -33,34 +41,28 @@ func randUint64() uint64 {
 // This is a port of wyhash implementation in runtime/hash64.go,
 // without using unsafe for purego.
 
-const (
-	m1 = 0xa0761d6478bd642f
-	m2 = 0xe7037ed1a0b428db
-	m3 = 0x8ebc6af09c88c6e3
-	m4 = 0x589965cc75374cc3
-	m5 = 0x1d8e4e27c47d124f
-)
+const m5 = 0x1d8e4e27c47d124f
 
 func wyhash(key []byte, seed, len uint64) uint64 {
 	p := key
 	i := len
 	var a, b uint64
-	seed ^= m1
+	seed ^= hashkey[0]
 
 	if i > 16 {
 		if i > 48 {
 			seed1 := seed
 			seed2 := seed
 			for ; i > 48; i -= 48 {
-				seed = mix(r8(p)^m2, r8(p[8:])^seed)
-				seed1 = mix(r8(p[16:])^m3, r8(p[24:])^seed1)
-				seed2 = mix(r8(p[32:])^m4, r8(p[40:])^seed2)
+				seed = mix(r8(p)^hashkey[1], r8(p[8:])^seed)
+				seed1 = mix(r8(p[16:])^hashkey[2], r8(p[24:])^seed1)
+				seed2 = mix(r8(p[32:])^hashkey[3], r8(p[40:])^seed2)
 				p = p[48:]
 			}
 			seed ^= seed1 ^ seed2
 		}
 		for ; i > 16; i -= 16 {
-			seed = mix(r8(p)^m2, r8(p[8:])^seed)
+			seed = mix(r8(p)^hashkey[1], r8(p[8:])^seed)
 			p = p[16:]
 		}
 	}
@@ -74,7 +76,7 @@ func wyhash(key []byte, seed, len uint64) uint64 {
 		a = r4(p)<<32 | r4(p[n:])
 		b = r4(p[i-4:])<<32 | r4(p[i-4-n:])
 	}
-	return mix(m5^len, mix(a^m2, b^seed))
+	return mix(m5^len, mix(a^hashkey[1], b^seed))
 }
 
 func r3(p []byte, k uint64) uint64 {