format: Move commitgraph and packfile here

1 files changed, 50 insertions, 0 deletions

diff --git a/format/commitgraph/bloom/settings.go b/format/commitgraph/bloom/settings.go
new file mode 100644
index 00000000..764653bd
--- /dev/null
+++ b/format/commitgraph/bloom/settings.go
@@ -0,0 +1,50 @@
+package bloom
+
+import (
+	"encoding/binary"
+
+	"codeberg.org/lindenii/furgit/internal/intconv"
+)
+
+// Settings describe the changed-paths Bloom filter parameters stored in
+// commit-graph BDAT chunks.
+//
+// Obviously, they must match the repository's commit-graph settings to
+// interpret filters correctly.
+type Settings struct {
+	HashVersion    uint32
+	NumHashes      uint32
+	BitsPerEntry   uint32
+	MaxChangePaths uint32
+}
+
+// ParseSettings reads Bloom filter settings from a BDAT chunk header.
+func ParseSettings(bdat []byte) (*Settings, error) {
+	if len(bdat) < DataHeaderSize {
+		return nil, ErrInvalid
+	}
+
+	settings := &Settings{
+		HashVersion:    binary.BigEndian.Uint32(bdat[0:4]),
+		NumHashes:      binary.BigEndian.Uint32(bdat[4:8]),
+		BitsPerEntry:   binary.BigEndian.Uint32(bdat[8:12]),
+		MaxChangePaths: DefaultMaxChange,
+	}
+
+	switch settings.HashVersion {
+	case 1, 2:
+	default:
+		return nil, ErrInvalid
+	}
+
+	if settings.NumHashes == 0 {
+		return nil, ErrInvalid
+	}
+
+	_, err := intconv.Uint32ToInt(settings.NumHashes)
+	if err != nil {
+		return nil, ErrInvalid
+	}
+
+	return settings, nil
+}