The Independent JPEG Group's JPEG software v6
diff --git a/jutils.c b/jutils.c
index ef10174..4ba2a54 100644
--- a/jutils.c
+++ b/jutils.c
@@ -1,12 +1,12 @@
/*
* jutils.c
*
- * Copyright (C) 1991-1994, Thomas G. Lane.
+ * Copyright (C) 1991-1995, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
- * This file contains miscellaneous utility routines needed for both
- * compression and decompression.
+ * This file contains tables and miscellaneous utility routines needed
+ * for both compression and decompression.
* Note we prefix all global names with "j" to minimize conflicts with
* a surrounding application.
*/
@@ -17,6 +17,50 @@
/*
+ * jpeg_zigzag_order[i] is the zigzag-order position of the i'th element
+ * of a DCT block read in natural order (left to right, top to bottom).
+ */
+
+const int jpeg_zigzag_order[DCTSIZE2] = {
+ 0, 1, 5, 6, 14, 15, 27, 28,
+ 2, 4, 7, 13, 16, 26, 29, 42,
+ 3, 8, 12, 17, 25, 30, 41, 43,
+ 9, 11, 18, 24, 31, 40, 44, 53,
+ 10, 19, 23, 32, 39, 45, 52, 54,
+ 20, 22, 33, 38, 46, 51, 55, 60,
+ 21, 34, 37, 47, 50, 56, 59, 61,
+ 35, 36, 48, 49, 57, 58, 62, 63
+};
+
+/*
+ * jpeg_natural_order[i] is the natural-order position of the i'th element
+ * of zigzag order.
+ *
+ * When reading corrupted data, the Huffman decoders could attempt
+ * to reference an entry beyond the end of this array (if the decoded
+ * zero run length reaches past the end of the block). To prevent
+ * wild stores without adding an inner-loop test, we put some extra
+ * "63"s after the real entries. This will cause the extra coefficient
+ * to be stored in location 63 of the block, not somewhere random.
+ * The worst case would be a run-length of 15, which means we need 16
+ * fake entries.
+ */
+
+const int jpeg_natural_order[DCTSIZE2+16] = {
+ 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,
+ 63, 63, 63, 63, 63, 63, 63, 63, /* extra entries for safety in decoder */
+ 63, 63, 63, 63, 63, 63, 63, 63
+};
+
+
+/*
* Arithmetic utilities
*/
@@ -116,7 +160,7 @@
GLOBAL void
jzero_far (void FAR * target, size_t bytestozero)
/* Zero out a chunk of FAR memory. */
-/* This might be sample-array data, block-array data, or alloc_medium data. */
+/* This might be sample-array data, block-array data, or alloc_large data. */
{
#ifdef FMEMZERO
FMEMZERO(target, bytestozero);