63 lines
1.8 KiB
C
63 lines
1.8 KiB
C
/* _PDCLIB_ftell64( FILE * )
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This file is part of the Public Domain C Library (PDCLib).
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Permission is granted to use, modify, and / or redistribute at will.
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*/
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#include <stdio.h>
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#include <stdint.h>
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#include <limits.h>
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#ifndef REGTEST
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#include "_PDCLIB_io.h"
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uint_fast64_t _PDCLIB_ftell64_unlocked( FILE * stream )
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{
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/* ftell() must take into account:
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- the actual *physical* offset of the file, i.e. the offset as recognized
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by the operating system (and stored in stream->pos.offset); and
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- any buffers held by PDCLib, which
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- in case of unwritten buffers, count in *addition* to the offset; or
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- in case of unprocessed pre-read buffers, count in *substraction* to
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the offset. (Remember to count ungetidx into this number.)
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Conveniently, the calculation ( ( bufend - bufidx ) + ungetidx ) results
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in just the right number in both cases:
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- in case of unwritten buffers, ( ( 0 - unwritten ) + 0 )
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i.e. unwritten bytes as negative number
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- in case of unprocessed pre-read, ( ( preread - processed ) + unget )
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i.e. unprocessed bytes as positive number.
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That is how the somewhat obscure return-value calculation works.
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*/
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/* ungetc on a stream at offset==0 will cause an overflow to UINT64_MAX.
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* C99/C11 says that the return value of ftell in this case is
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* "indeterminate"
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*/
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return ( stream->pos.offset - ( ( (int)stream->bufend - (int)stream->bufidx ) + (int)stream->ungetidx ) );
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}
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uint_fast64_t _PDCLIB_ftell64( FILE * stream )
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{
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_PDCLIB_flockfile( stream );
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uint_fast64_t pos = _PDCLIB_ftell64_unlocked( stream );
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_PDCLIB_funlockfile( stream );
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return pos;
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}
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#endif
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#ifdef TEST
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#include "_PDCLIB_test.h"
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#include <stdlib.h>
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int main( void )
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{
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/* Tested by ftell */
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return TEST_RESULTS;
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}
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#endif
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