1 files changed, 68 insertions, 0 deletions
diff --git a/object/id/algorithm_details.go b/object/id/algorithm_details.go
new file mode 100644
index 00000000..d3fd665d
--- /dev/null
+++ b/object/id/algorithm_details.go
@@ -0,0 +1,68 @@
+package id
+
+import (
+	"crypto/sha1" //#nosec:G505
+	"crypto/sha256"
+	"hash"
+)
+
+type algorithmDetails struct {
+	name                string
+	size                int
+	packHashID          uint32
+	signatureHeaderName string
+	sum                 func([]byte) ObjectID
+	new                 func() hash.Hash
+	emptyTree           ObjectID
+}
+
+func (algo Algorithm) info() algorithmDetails {
+	return algorithmTable[algo]
+}
+
+//nolint:gochecknoglobals
+var algorithmTable = [...]algorithmDetails{
+	AlgorithmUnknown: {},
+	AlgorithmSHA1: {
+		name:                "sha1",
+		size:                sha1.Size,
+		packHashID:          1,
+		signatureHeaderName: "gpgsig",
+		new:                 sha1.New,
+	},
+	AlgorithmSHA256: {
+		name:                "sha256",
+		size:                sha256.Size,
+		packHashID:          2,
+		signatureHeaderName: "gpgsig-sha256",
+		new:                 sha256.New,
+	},
+}
+
+// maxObjectIDSize MUST be >= the largest supported algorithm size.
+const maxObjectIDSize = sha256.Size
+
+var (
+	//nolint:gochecknoglobals
+	algorithmByName = map[string]Algorithm{}
+	//nolint:gochecknoglobals
+	algorithmBySignatureHeaderName = map[string]Algorithm{}
+	//nolint:gochecknoglobals
+	supportedAlgorithms []Algorithm
+)
+
+func init() { //nolint:gochecknoinits
+	// Skip over AlgorithmUnknown.
+	for algo := Algorithm(1); int(algo) < len(algorithmTable); algo++ {
+		info := &algorithmTable[algo]
+
+		info.emptyTree = info.sum([]byte("tree 0\x00"))
+
+		algorithmByName[info.name] = algo
+		if info.signatureHeaderName != "" {
+			algorithmBySignatureHeaderName[info.signatureHeaderName] = algo
+		}
+
+		supportedAlgorithms = append(supportedAlgorithms, algo)
+	}
+}