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48 lines
1.6 KiB
48 lines
1.6 KiB
/*****************************************************************************
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* *
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* ZECKDAT.H *
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* *
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* Copyright (C) Microsoft Corporation 1990. *
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* All Rights reserved. *
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* *
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******************************************************************************
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* *
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* Module Intent *
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* *
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* Internal data decls for Zeck compression routines for bitmaps & topic
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* 2K blocks.
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* *
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*****************************************************************************/
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/* ----- THIS STUFF USED INTERNALLY BY THE COMPRESSION ROUTINES ----- */
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#ifndef HC_H
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#include "hc.h"
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#endif
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// this bitfield structure encodes an offset and a length of the
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// repeated pattern. Since we deal with huge buffers, we must access
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// this as two bytes to insert it into the buffer (structures cannot
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// cross huge segment boundaries).
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typedef union bytesoverlay {
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struct {
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WORD uiBackwardsOffset:12;
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WORD cbPatternLen:4;
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};
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BYTE bytes[2];
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} ZECKPACKBLOCK, *QZECKPACKBLOCK;
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// The length encoding is offset by a min value since you would never
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// encode a pattern of 1 or 2 bytes. And no, you can't change MAX_PATTERN_LEN
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// The decompression code (i.e., WinHelp) depends on these values.
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#define MIN_PATTERN_LEN 3
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#define MAX_PATTERN_LEN 18
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#define PATTERNLEN_FROM_ENCODE(len) ((len) + MIN_PATTERN_LEN)
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#define ENCODE_FROM_PATTERNLEN(len) ((len) - MIN_PATTERN_LEN)
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// do similar offset for backwards offset:
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#define BACKWARDS_FROM_ENCODE(offset) ((offset) + 1)
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#define ENCODE_FROM_BACKWARDS(offset) ((offset) -1)
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