...

pkg/data/ourdb/location.go

@@ -0,0 +1,150 @@
+package ourdb
+
+import (
+	"errors"
+	"fmt"
+)
+
+// Location represents a position in a database file
+type Location struct {
+	FileNr   uint16
+	Position uint32
+}
+
+// LocationNew creates a new Location from bytes
+func (lut *LookupTable) LocationNew(b_ []byte) (Location, error) {
+	newLocation := Location{
+		FileNr:   0,
+		Position: 0,
+	}
+
+	// First verify keysize is valid
+	if lut.KeySize != 2 && lut.KeySize != 3 && lut.KeySize != 4 && lut.KeySize != 6 {
+		return newLocation, errors.New("keysize must be 2, 3, 4 or 6")
+	}
+
+	// Create padded b
+	b := make([]byte, lut.KeySize)
+	startIdx := int(lut.KeySize) - len(b_)
+	if startIdx < 0 {
+		return newLocation, errors.New("input bytes exceed keysize")
+	}
+
+	for i := 0; i < len(b_); i++ {
+		b[startIdx+i] = b_[i]
+	}
+
+	switch lut.KeySize {
+	case 2:
+		// Only position, 2 bytes big endian
+		newLocation.Position = uint32(b[0])<<8 | uint32(b[1])
+		newLocation.FileNr = 0
+	case 3:
+		// Only position, 3 bytes big endian
+		newLocation.Position = uint32(b[0])<<16 | uint32(b[1])<<8 | uint32(b[2])
+		newLocation.FileNr = 0
+	case 4:
+		// Only position, 4 bytes big endian
+		newLocation.Position = uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
+		newLocation.FileNr = 0
+	case 6:
+		// 2 bytes file_nr + 4 bytes position, all big endian
+		newLocation.FileNr = uint16(b[0])<<8 | uint16(b[1])
+		newLocation.Position = uint32(b[2])<<24 | uint32(b[3])<<16 | uint32(b[4])<<8 | uint32(b[5])
+	}
+
+	// Verify limits based on keysize
+	switch lut.KeySize {
+	case 2:
+		if newLocation.Position > 0xFFFF {
+			return newLocation, errors.New("position exceeds max value for keysize=2 (max 65535)")
+		}
+		if newLocation.FileNr != 0 {
+			return newLocation, errors.New("file_nr must be 0 for keysize=2")
+		}
+	case 3:
+		if newLocation.Position > 0xFFFFFF {
+			return newLocation, errors.New("position exceeds max value for keysize=3 (max 16777215)")
+		}
+		if newLocation.FileNr != 0 {
+			return newLocation, errors.New("file_nr must be 0 for keysize=3")
+		}
+	case 4:
+		if newLocation.FileNr != 0 {
+			return newLocation, errors.New("file_nr must be 0 for keysize=4")
+		}
+	case 6:
+		// For keysize 6: both file_nr and position can use their full range
+		// No additional checks needed as u16 and u32 already enforce limits
+	}
+
+	return newLocation, nil
+}
+
+// ToBytes converts a Location to a 6-byte array
+func (loc Location) ToBytes() ([]byte, error) {
+	bytes := make([]byte, 6)
+
+	// Put file_nr first (2 bytes)
+	bytes[0] = byte(loc.FileNr >> 8)
+	bytes[1] = byte(loc.FileNr)
+
+	// Put position next (4 bytes)
+	bytes[2] = byte(loc.Position >> 24)
+	bytes[3] = byte(loc.Position >> 16)
+	bytes[4] = byte(loc.Position >> 8)
+	bytes[5] = byte(loc.Position)
+
+	return bytes, nil
+}
+
+// ToLookupBytes converts a Location to bytes according to the keysize
+func (loc Location) ToLookupBytes(keysize uint8) ([]byte, error) {
+	bytes := make([]byte, keysize)
+
+	switch keysize {
+	case 2:
+		if loc.Position > 0xFFFF {
+			return nil, errors.New("position exceeds max value for keysize=2 (max 65535)")
+		}
+		if loc.FileNr != 0 {
+			return nil, errors.New("file_nr must be 0 for keysize=2")
+		}
+		bytes[0] = byte(loc.Position >> 8)
+		bytes[1] = byte(loc.Position)
+	case 3:
+		if loc.Position > 0xFFFFFF {
+			return nil, errors.New("position exceeds max value for keysize=3 (max 16777215)")
+		}
+		if loc.FileNr != 0 {
+			return nil, errors.New("file_nr must be 0 for keysize=3")
+		}
+		bytes[0] = byte(loc.Position >> 16)
+		bytes[1] = byte(loc.Position >> 8)
+		bytes[2] = byte(loc.Position)
+	case 4:
+		if loc.FileNr != 0 {
+			return nil, errors.New("file_nr must be 0 for keysize=4")
+		}
+		bytes[0] = byte(loc.Position >> 24)
+		bytes[1] = byte(loc.Position >> 16)
+		bytes[2] = byte(loc.Position >> 8)
+		bytes[3] = byte(loc.Position)
+	case 6:
+		bytes[0] = byte(loc.FileNr >> 8)
+		bytes[1] = byte(loc.FileNr)
+		bytes[2] = byte(loc.Position >> 24)
+		bytes[3] = byte(loc.Position >> 16)
+		bytes[4] = byte(loc.Position >> 8)
+		bytes[5] = byte(loc.Position)
+	default:
+		return nil, fmt.Errorf("invalid keysize: %d", keysize)
+	}
+
+	return bytes, nil
+}
+
+// ToUint64 converts a Location to uint64, with file_nr as most significant (big endian)
+func (loc Location) ToUint64() (uint64, error) {
+	return (uint64(loc.FileNr) << 32) | uint64(loc.Position), nil
+}