return nil
	}
	c := Checksum{Type: alg, Encoded: value, Raw: bvalue, WantParts: wantParts}
	if !c.Valid() {
		return nil
	}
	return &c
}

// NewChecksumString returns a new checksum from specified algorithm and base64 encoded value.
func NewChecksumString(alg, value string) *Checksum {
	return NewChecksumWithType(NewChecksumType(alg, ""), value)
}

// AppendTo will append the checksum to b.

				return oi, InvalidPart{
					PartNumber: part.PartNumber,
					ExpETag:    wantCS[checksumType.String()],
					GotETag:    crc,
				}
			}
			cs := hash.NewChecksumString(checksumType.String(), crc)
			if !cs.Valid() {
				return oi, InvalidPart{
					PartNumber: part.PartNumber,
				}
			}
			if checksumType.FullObjectRequested() {