+#ifndef _ZIGZAG_H
+#define _ZIGZAG_H
+
+#include "idct.h"
+
+// Table for transforming from zig-zag order to natural order.
+// We use the same trick as libjpeg here; there are 16 extra entries
+// after the end of the table, since the run-length decoder could
+// potentially cause entries indices >= 64 to be decoded.
+static const unsigned unzigzag[DCTSIZE2 + 16] = {
+ // Regular entries.
+ 0, 1, 8, 16, 9, 2, 3, 10,
+ 17, 24, 32, 25, 18, 11, 4, 5,
+ 12, 19, 26, 33, 40, 48, 41, 34,
+ 27, 20, 13, 6, 7, 14, 21, 28,
+ 35, 42, 49, 56, 57, 50, 43, 36,
+ 29, 22, 15, 23, 30, 37, 44, 51,
+ 58, 59, 52, 45, 38, 31, 39, 46,
+ 53, 60, 61, 54, 47, 55, 62, 63,
+
+ // Extra padding entries; should never be referenced in well-formed data.
+ 63, 63, 63, 63, 63, 63, 63, 63,
+ 63, 63, 63, 63, 63, 63, 63, 63,
+};
+
+#endif /* !defined(_ZIGZAG_H) */