115 lines
3.4 KiB
C
115 lines
3.4 KiB
C
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/***
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*mbsdec.c - Move MBCS string pointer backward one charcter.
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*
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* Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* Move MBCS string pointer backward one character.
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*
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*Revision History:
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* 11-19-92 KRS Ported from 16-bit sources.
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* 08-03-93 KRS Fix prototypes.
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* 08-20-93 CFW Remove test for NULL string, use new function parameters.
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* 10-05-93 GJF Replaced _CRTAPI1 with __cdecl.
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* 04-15-93 CFW Add _MB_CP_LOCK.
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* 05-09-94 CFW Optimize for SBCS.
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* 05-13-94 CFW Fix SBCS optimization.
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* 05-19-94 CFW Enable non-Win32.
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* 09-11-97 GJF Replaced __mbcodepage == 0 with _ISNOTMBCP.
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* 04-07-98 GJF Revised multithread support based on threadmbcinfo
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* structs
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*
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*******************************************************************************/
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#ifdef _MBCS
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#include <mtdll.h>
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#include <cruntime.h>
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#include <mbdata.h>
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#include <mbstring.h>
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#include <mbctype.h>
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#include <stddef.h>
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/***
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*_mbsdec - Move MBCS string pointer backward one charcter.
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*
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*Purpose:
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* Move the supplied string pointer backwards by one
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* character. MBCS characters are handled correctly.
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*
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*Entry:
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* const unsigned char *string = pointer to beginning of string
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* const unsigned char *current = current char pointer (legal MBCS boundary)
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*
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*Exit:
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* Returns pointer after moving it.
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* Returns NULL if string >= current.
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*
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*Exceptions:
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*
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*******************************************************************************/
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unsigned char * __cdecl _mbsdec(
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const unsigned char *string,
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const unsigned char *current
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)
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{
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const unsigned char *temp;
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#ifdef _MT
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pthreadmbcinfo ptmbci = _getptd()->ptmbcinfo;
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if ( ptmbci != __ptmbcinfo )
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ptmbci = __updatetmbcinfo();
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#endif
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if (string >= current)
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return(NULL);
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#ifdef _MT
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if ( _ISNOTMBCP_MT(ptmbci) )
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#else
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if ( _ISNOTMBCP )
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#endif
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return (unsigned char *)--current;
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temp = current - 1;
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/*
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* If (current-1) returns true from _ISLEADBTYE, it is a trail byte, because
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* it is not a legal single byte MBCS character. Therefore, is so, return
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* (current-2) because it is the trailbyte's lead.
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*/
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#ifdef _MT
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if ( __ismbblead_mt(ptmbci, *temp) )
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#else
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if ( _ismbblead(*temp) )
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#endif
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return (unsigned char *)(temp - 1);
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/*
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* It is unknown whether (current - 1) is a single byte character or a
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* trail. Now decrement temp until
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* a) The beginning of the string is reached, or
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* b) A non-lead byte (either single or trail) is found.
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* The difference between (current-1) and temp is the number of non-single
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* byte characters preceding (current-1). There are two cases for this:
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* a) (current - temp) is odd, and
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* b) (current - temp) is even.
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* If odd, then there are an odd number of "lead bytes" preceding the
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* single/trail byte (current - 1), indicating that it is a trail byte.
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* If even, then there are an even number of "lead bytes" preceding the
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* single/trail byte (current - 1), indicating a single byte character.
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*/
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#ifdef _MT
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while ( (string <= --temp) && (__ismbblead_mt(ptmbci, *temp)) )
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#else
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while ( (string <= --temp) && (_ismbblead(*temp)) )
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#endif
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;
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return (unsigned char *)(current - 1 - ((current - temp) & 0x01) );
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}
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#endif /* _MBCS */
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