- /* ftell() must take into account:
- - the actual *physical* offset of the file, i.e. the offset as recognized
- by the operating system (and stored in stream->pos.offset); and
- - any buffers held by PDCLib, which
- - in case of unwritten buffers, count in *addition* to the offset; or
- - in case of unprocessed pre-read buffers, count in *substraction* to
- the offset. (Remember to count ungetidx into this number.)
- Conveniently, the calculation ( ( bufend - bufidx ) + ungetidx ) results
- in just the right number in both cases:
- - in case of unwritten buffers, ( ( 0 - unwritten ) + 0 )
- i.e. unwritten bytes as negative number
- - in case of unprocessed pre-read, ( ( preread - processed ) + unget )
- i.e. unprocessed bytes as positive number.
- That is how the somewhat obscure return-value calculation works.
- */
- /* If offset is too large for return type, report error instead of wrong
- offset value. Buffers may not be larger than INT_MAX so the casts are
- safe.
- */
- /* FIXME: This calculation *underflows* when offset smaller than pre-read */
- if ( ( stream->pos.offset - ( (int)stream->bufend + (int)stream->ungetidx ) ) > ( LONG_MAX - stream->bufidx ) )