1 files changed, 70 insertions, 42 deletions

diff --git a/hash.go b/hash.go
index df39ac30..cbaac821 100644
--- a/hash.go
+++ b/hash.go
@@ -6,59 +6,74 @@ import (
 	"encoding/hex"
 )
 
-// maxHashSize MUST be equal to (or larger than) the size of the
-// largest hash supported in hashFuncs.
+// maxHashSize MUST be >= the largest supported algorithm size.
 const maxHashSize = sha256.Size
 
 // hashAlgorithm identifies the hash algorithm used for Git object IDs.
 type hashAlgorithm uint8
 
-// hashFuncs maps hash algorithm to hash function.
-var hashFuncs = map[hashAlgorithm]hashFunc{
-	hashAlgoSHA1: func(data []byte) Hash {
-		sum := sha1.Sum(data)
-		var h Hash
-		copy(h.data[:], sum[:])
-		h.algo = hashAlgoSHA1
-		return h
-	},
-	hashAlgoSHA256: func(data []byte) Hash {
-		sum := sha256.Sum256(data)
-		var h Hash
-		copy(h.data[:], sum[:])
-		h.algo = hashAlgoSHA256
-		return h
-	},
-}
-
 const (
 	hashAlgoUnknown hashAlgorithm = iota
 	hashAlgoSHA1
 	hashAlgoSHA256
 )
 
-// size returns the hash size in bytes.
-func (algo hashAlgorithm) size() int {
-	switch algo {
-	case hashAlgoSHA1:
-		return sha1.Size
-	case hashAlgoSHA256:
-		return sha256.Size
-	default:
-		return 0
-	}
+type hashAlgorithmDetails struct {
+	name string
+	size int
+	sum  func([]byte) Hash
+}
+
+var hashAlgorithmTable = [...]hashAlgorithmDetails{
+	hashAlgoUnknown: {},
+	hashAlgoSHA1: {
+		name: "sha1",
+		size: sha1.Size,
+		sum: func(data []byte) Hash {
+			sum := sha1.Sum(data)
+			var h Hash
+			copy(h.data[:], sum[:])
+			h.algo = hashAlgoSHA1
+			return h
+		},
+	},
+	hashAlgoSHA256: {
+		name: "sha256",
+		size: sha256.Size,
+		sum: func(data []byte) Hash {
+			sum := sha256.Sum256(data)
+			var h Hash
+			copy(h.data[:], sum[:])
+			h.algo = hashAlgoSHA256
+			return h
+		},
+	},
+}
+
+func (algo hashAlgorithm) info() hashAlgorithmDetails {
+	return hashAlgorithmTable[algo]
+}
+
+// Size returns the hash size in bytes.
+func (algo hashAlgorithm) Size() int {
+	return algo.info().size
 }
 
 // String returns the canonical name of the hash algorithm.
 func (algo hashAlgorithm) String() string {
-	switch algo {
-	case hashAlgoSHA1:
-		return "sha1"
-	case hashAlgoSHA256:
-		return "sha256"
-	default:
+	inf := algo.info()
+	if inf.name == "" {
 		return "unknown"
 	}
+	return inf.name
+}
+
+func (algo hashAlgorithm) HexLen() int {
+	return algo.Size() * 2
+}
+
+func (algo hashAlgorithm) Sum(data []byte) Hash {
+	return algo.info().sum(data)
 }
 
 // Hash represents a Git object ID.
@@ -67,12 +82,9 @@ type Hash struct {
 	data [maxHashSize]byte
 }
 
-// hashFunc is a function that computes a hash from input data.
-type hashFunc func([]byte) Hash
-
 // String returns a hexadecimal string representation of the hash.
 func (hash Hash) String() string {
-	size := hash.algo.size()
+	size := hash.algo.Size()
 	if size == 0 {
 		return ""
 	}
@@ -81,7 +93,7 @@ func (hash Hash) String() string {
 
 // Bytes returns a copy of the hash's bytes.
 func (hash Hash) Bytes() []byte {
-	size := hash.algo.size()
+	size := hash.algo.Size()
 	if size == 0 {
 		return nil
 	}
@@ -90,5 +102,21 @@ func (hash Hash) Bytes() []byte {
 
 // Size returns the hash size.
 func (hash Hash) Size() int {
-	return hash.algo.size()
+	return hash.algo.Size()
+}
+
+var algoByName = map[string]hashAlgorithm{}
+
+func init() {
+	for algo, info := range hashAlgorithmTable {
+		if info.name == "" {
+			continue
+		}
+		algoByName[info.name] = hashAlgorithm(algo)
+	}
+}
+
+func parseHashAlgorithm(s string) (hashAlgorithm, bool) {
+	algo, ok := algoByName[s]
+	return algo, ok
 }