cmd/internal: add hash package

To be used in compiler toolchain instead of notsha256.

Change-Id: Iceeacb6df7dfa7111ec98f070eba8e27a4ddbe8b
Reviewed-on: https://go-review.googlesource.com/c/go/+/610595
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

src/cmd/internal/hash/hash.go

@@ -0,0 +1,56 @@
+// Copyright 2024 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.
+
+// Package hash implements hash functions used in the compiler toolchain.
+package hash
+
+import (
+	"crypto/md5"
+	"crypto/sha1"
+	"crypto/sha256"
+	"hash"
+)
+
+const (
+	// Size32 is the size of 32 bytes hash checksum.
+	Size32 = sha256.Size
+	// Size20 is the size of 20 bytes hash checksum.
+	Size20 = sha1.Size
+	// Size16 is the size of 16 bytes hash checksum.
+	Size16 = md5.Size
+)
+
+// New32 returns a new [hash.Hash] computing the 32 bytes hash checksum.
+func New32() hash.Hash {
+	h := sha256.New()
+	_, _ = h.Write([]byte{1}) // make this hash different from sha256
+	return h
+}
+
+// New20 returns a new [hash.Hash] computing the 20 bytes hash checksum.
+func New20() hash.Hash {
+	return sha1.New()
+}
+
+// New16 returns a new [hash.Hash] computing the 16 bytes hash checksum.
+func New16() hash.Hash {
+	return md5.New()
+}
+
+// Sum32 returns the 32 bytes checksum of the data.
+func Sum32(data []byte) [Size32]byte {
+	sum := sha256.Sum256(data)
+	sum[0] ^= 1 // make this hash different from sha256
+	return sum
+}
+
+// Sum20 returns the 20 bytes checksum of the data.
+func Sum20(data []byte) [Size20]byte {
+	return sha1.Sum(data)
+}
+
+// Sum16 returns the 16 bytes checksum of the data.
+func Sum16(data []byte) [Size16]byte {
+	return md5.Sum(data)
+}