| 1 | /*
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| 2 | * jutils.c
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| 3 | *
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| 4 | * Copyright (C) 1991-1996, Thomas G. Lane.
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| 5 | * This file is part of the Independent JPEG Group's software.
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| 6 | * For conditions of distribution and use, see the accompanying README file.
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| 7 | *
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| 8 | * This file contains tables and miscellaneous utility routines needed
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| 9 | * for both compression and decompression.
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| 10 | * Note we prefix all global names with "j" to minimize conflicts with
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| 11 | * a surrounding application.
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| 12 | */
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| 13 |
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| 14 | #define JPEG_INTERNALS
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| 15 | #include "jinclude.h"
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| 16 | #include "jpeglib.h"
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| 17 |
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| 18 |
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| 19 | /*
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| 20 | * jpeg_zigzag_order[i] is the zigzag-order position of the i'th element
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| 21 | * of a DCT block read in natural order (left to right, top to bottom).
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| 22 | */
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| 23 |
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| 24 | #if 0 /* This table is not actually needed in v6a */
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| 25 |
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| 26 | const int jpeg_zigzag_order[DCTSIZE2] = {
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| 27 | 0, 1, 5, 6, 14, 15, 27, 28,
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| 28 | 2, 4, 7, 13, 16, 26, 29, 42,
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| 29 | 3, 8, 12, 17, 25, 30, 41, 43,
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| 30 | 9, 11, 18, 24, 31, 40, 44, 53,
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| 31 | 10, 19, 23, 32, 39, 45, 52, 54,
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| 32 | 20, 22, 33, 38, 46, 51, 55, 60,
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| 33 | 21, 34, 37, 47, 50, 56, 59, 61,
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| 34 | 35, 36, 48, 49, 57, 58, 62, 63
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| 35 | };
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| 36 |
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| 37 | #endif
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| 38 |
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| 39 | /*
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| 40 | * jpeg_natural_order[i] is the natural-order position of the i'th element
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| 41 | * of zigzag order.
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| 42 | *
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| 43 | * When reading corrupted data, the Huffman decoders could attempt
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| 44 | * to reference an entry beyond the end of this array (if the decoded
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| 45 | * zero run length reaches past the end of the block). To prevent
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| 46 | * wild stores without adding an inner-loop test, we put some extra
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