static uint GetPrevChar( b_file *io ) {
//=========================================
// Get previous character in file.
if( CurrFileOffset( io ) == 0 ) return( NO_CHAR );
if( SysSeek( io, -1L, SEEK_CUR ) < 0 ) {
return( NO_CHAR );
}
if( ( io->attrs & READ_AHEAD ) && io->b_curs < io->read_len ) {
return( io->buffer[ io->b_curs ] );
} else if( io->b_curs < io->high_water ) {
return( io->buffer[ io->b_curs ] );
}
return( NO_CHAR );
}
int SysSeek( b_file *io, long int new_offset, int seek_mode )
{
long int curr_offset;
long int new_page;
long int page_offset;
uint bytes_read;
curr_offset = CurrFileOffset( io );
if( seek_mode == SEEK_CUR ) {
new_offset += curr_offset;
}
if( io->attrs & WRITE_ONLY ) {
if( curr_offset != new_offset ) {
if( FlushBuffer( io ) < 0 ) {
FSetSysErr( io );
return( -1 );
}
if( lseek( io->handle, new_offset, SEEK_SET ) == -1 ) {
FSetSysErr( io );
return( -1 );
}
io->phys_offset = new_offset;
}
return( 0 );
} else if( io->attrs & READ_AHEAD ) {
page_offset = io->phys_offset - io->read_len;
if( page_offset <= new_offset ) {
if( (new_offset < io->phys_offset) ||
( (io->attrs & PAST_EOF) &&
(new_offset < page_offset + io->buff_size) ) ) {
// we have the part of file in memory still, or we know we're
// at the end of the file and the offset we want is on this
// page as well
io->b_curs = new_offset - io->phys_offset + io->read_len;
return( 0 );
}
}
} else if( io->phys_offset <= new_offset &&
new_offset < io->phys_offset + io->buff_size ) {
io->b_curs = new_offset - io->phys_offset;
if( ( io->attrs & PAST_EOF ) || io->b_curs < io->high_water ) {
// We already know that the EOF is on this page so don't bother
// seeking and reading. Or we already have the part of the
// file in the buffer.
return( 0 );
}
// we have part of this page in memory already... so read the
// rest of the page
if( lseek( io->handle, io->high_water, SEEK_CUR ) < 0 ) {
FSetSysErr( io );
return( -1 );
}
io->phys_offset += io->high_water;
bytes_read = readbytes( io, io->buffer + io->high_water,
io->buff_size - io->high_water );
if( bytes_read == READ_ERROR ) {
if( io->stat != IO_EOF ) return( -1 );
IOOk( io );
io->phys_offset -= io->high_water; // restore offset
if( lseek( io->handle, -(long)io->high_water, SEEK_CUR ) < 0 ) {
FSetSysErr( io );
return( -1 );
}
io->attrs |= PAST_EOF; // we now know the EOF is here
} else {
io->attrs |= READ_AHEAD;
io->read_len = io->high_water + bytes_read;
if( bytes_read < io->buff_size - io->high_water ) {
io->attrs |= PAST_EOF; // we now know the EOF is here
}
}
return( 0 );
}
if( new_offset != curr_offset ) {
if( FlushBuffer( io ) < 0 ) return( 0 );
// round down to the nearest multiple of buff_size
new_page = new_offset - new_offset % io->buff_size;
if( lseek( io->handle, new_page, SEEK_SET ) < 0 ) {
FSetSysErr( io );
return( -1 );
}
io->phys_offset = new_page;
io->b_curs = new_offset - new_page;
bytes_read = readbytes( io, io->buffer, io->buff_size );
if( bytes_read == READ_ERROR ) {
if( io->stat != IO_EOF ) return( -1 );
IOOk( io );
io->attrs |= PAST_EOF;
} else {
if( bytes_read < io->buff_size ) {
io->attrs |= PAST_EOF;
} else {
io->attrs &= ~PAST_EOF;
}
io->attrs |= READ_AHEAD;
io->read_len = bytes_read;
}
}
return( 0 );
}
long int FGetFilePos( b_file *io )
{
return( CurrFileOffset( io ) );
}
