INT 2C P - RM386 v6.00 - CLOAKING - ALLOCATE GDT SELECTOR
        AX = 0000h
        EBX = base address
        CL = access mode byte
        CH = extended access mode byte (omit limit field)
        EDX = segment limit
Return: CF clear if successful
            AX = selector
        CF set on error
            AX = error code (see below)
Program: RM386 (RAM-MAN/386) is the memory manager included in Helix Software's
          Netroom
Note:   this INT 2C interface is used by Netroom's DPMI.EXE v3.00
SeeAlso: AX=0001h,AX=0002h,AX=0003h,AX=0004h,AX=0005h,INT 31/AH=57h

Values for error code:
 0001h  no more selectors
 0002h  not a GDT ring 0 selector
 0003h  invalid selector (out of range, not user selector)
 0004h  selector not allocated

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