- ensure es = ds = ss upon exit of each C runtime function
- clear upper 16 bits of ebx before setting them to 0x0021,
when invoking interrupt_ptr to simulate a RM int 0x21
- make _sys_exists use the transfer buffer (which it needs)
- make _sys_rawread properly handle an end-of-file read
(zero bytes read)
- make argument to _sys_seterrno short --- after a failed
int 0x21 call, only the lower 16 bits of eax hold the MS-DOs
error code
- _sys_rawlseek accepts only 3 longword arguments, not 4
(the offset is only 1 longword)
- other minor fixes
