DOS Extender functions
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 The following functions are for use with the Blinker DOS extender. They will
 seldom have meaningful effects or return meaningful information except when
 used with the DOS extender.

 In the subsequent discussions and examples, the following terms are used:

 Descriptor A structure containing the size, base and attributes of a
            protected mode segment.

 Paragraph  The segment portion of a real mode address, eg the paragraph of
            the colour adapter is B800h.

 Segment    The actual code or data unit as allocated and stored in memory.

 Selector   The value used to identify a segment when running in protected
            mode, i.e. that is passed to and from the protected mode memory
            allocation functions.

 All functions assume the following definitions from the include file
 BLX286.H which can be found in the C subdirectory of the Blinker
 installation directory:

    typedef unsigned char BYTE;
    typedef unsigned short SEL;
    typedef unsigned short USHORT;
    typedef unsigned long ULONG;
    typedef unsigned short _far *PSEL;
    typedef struct
       {
       ULONG segbase;    /* Segment linear base address */
       ULONG seglen;        /* Segment length in bytes */
       USHORT segattrib; /* Segment attribute bytes */
       } DESC;              /* This is not a real descriptor */
    #define BLXAPI pascal _far