BLK_CUR_FILEPOS
BLK_CUR_FILEPOS = 0;
if (filepos < BLK_CUR_FILEPOS)
BLK_CUR_FILEPOS = 0;
while (filepos > BLK_CUR_FILEPOS)
if ((filepos - (BLK_CUR_FILEPOS & ~(SECTOR_SIZE - 1)))
BLK_CUR_FILEPOS += SECTOR_SIZE;
BLK_CUR_FILEPOS = filepos;