init: v1.0.0

sm/hash.go

@@ -0,0 +1,101 @@
+package sm
+
+import (
+	"crypto"
+	"hash"
+)
+
+// Hash identifies a cryptographic hash function that is implemented in another
+// package.
+// I try to keep it consistent with the standard library
+type Hash struct {
+	crypto.Hash
+}
+
+// HashFunc simply returns the value of h so that Hash implements SignerOpts.
+func (h Hash) HashFunc() crypto.Hash {
+	return h.Hash
+}
+
+func (h Hash) String() string {
+	switch h {
+	case SM3:
+		return "SM3"
+	case SM3WithID:
+		return "SM3WithID"
+	default:
+		// return ""
+		return h.Hash.String()
+	}
+}
+
+var (
+	SM3       Hash
+	SM3WithID Hash
+	maxHash   Hash
+)
+var SHA1 = Hash{crypto.SHA1}
+var SHA256 = Hash{crypto.SHA256}
+
+func init() {
+	// A hack to get the maxHash in crypto.
+	i := new(crypto.Hash)
+	*i = 1
+	defer func() {
+		_ = recover()
+		SM3 = Hash{Hash: *i}
+		SM3WithID = Hash{Hash: *i + 1}
+		maxHash = Hash{Hash: *i + 2}
+	}()
+	for {
+		(*i).Size()
+		*i++
+	}
+}
+
+// Size returns the length, in bytes, of a digest resulting from the given hash
+// function. It doesn't require that the hash function in question be linked
+// into the program.
+func (h Hash) Size() int {
+	switch h {
+	case SM3, SM3WithID:
+		return 32
+	default:
+		return h.Hash.Size()
+	}
+}
+
+var hashes = make(map[Hash]func() hash.Hash)
+
+// New returns a new hash.Hash calculating the given hash function. New panics
+// if the hash function is not linked into the binary.
+func (h Hash) New() hash.Hash {
+	if h.Hash >= SM3.Hash && h.Hash < maxHash.Hash {
+		f := hashes[h]
+		if f != nil {
+			return f()
+		}
+	}
+	return h.Hash.New()
+}
+
+// Available reports whether the given hash function is linked into the binary.
+func (h Hash) Available() bool {
+	if h.Hash >= SM3.Hash && h.Hash < maxHash.Hash {
+		return true
+	}
+	return h.Hash.Available()
+}
+
+// RegisterHash registers a function that returns a new instance of the given
+// hash function. This is intended to be called from the init function in
+// packages that implement hash functions.
+func RegisterHash(h Hash, f func() hash.Hash) {
+	if h.Hash >= maxHash.Hash {
+		panic("crypto: RegisterHash of unknown hash function")
+	}
+	// if h.Hash < SM3.Hash {
+	// crypto.RegisterHash(h.Hash, f)
+	// }
+	hashes[h] = f
+}