func (b *block) toSparse() sparseArray { return sparseArray(b[:]) }

// getFormat checks that the block is a valid tar header based on the checksum.
// It then attempts to guess the specific format based on magic values.
// If the checksum fails, then FormatUnknown is returned.
func (b *block) getFormat() Format {
	// Verify checksum.
	var p parser
	value := p.parseOctal(b.toV7().chksum())

	// other fields in Header take precedence over PAXRecords.
	PAXRecords map[string]string

	// Format specifies the format of the tar header.
	//
	// This is set by Reader.Next as a best-effort guess at the format.
	// Since the Reader liberally reads some non-compliant files,
	// it is possible for this to be FormatUnknown.
	//
	// If the format is unspecified when Writer.WriteHeader is called,

					n.Kind = "sconst"
					n.Const = n.Define
				}
			}

			if n.IsConst() {
				continue
			}
		}

		// If this is a struct, union, or enum type name, no need to guess the kind.
		if strings.HasPrefix(n.C, "struct ") || strings.HasPrefix(n.C, "union ") || strings.HasPrefix(n.C, "enum ") {
			n.Kind = "type"
			needType = append(needType, n)
			continue
		}

			// section; there must be a preceding call to handleRegularFile.
			if err := tr.handleSparseFile(hdr, rawHdr); err != nil {
				return nil, err
			}

			// Set the final guess at the format.
			if format.has(FormatUSTAR) && format.has(FormatPAX) {
				format.mayOnlyBe(FormatUSTAR)
			}
			hdr.Format = format
			return hdr, nil // This is a file, so stop
		}
	}
}