Compatibility: DPMI 0.9+
Expects: AX    168AH
DS:SI address of ASCIIZ  string identifying the vendor
                                                                  
Returns: AX    0000h = successful
else  = no such vendor API or not in Protected Mode
ES:DI vendor-specific API Entry Address
                                                                  
Info: A DPMI client may use this fn to get an address that will provide
access to vendor-specific extensions of the DPMI specification.

DS:(E)SI the string at this address must match exactly with the vendor ID.
The string comparison is case-sensitive.

ES:(E)DI on return, this is the address supplied by the vendor.  Access it
via a FAR CALL.  Registers and other calling conventions are set
by the vendor.

Note: You must be in protected mode to call this.

See Also: DPMI API
INT 2fH 16xxH (Enh386 Windows Services & Notifications)
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INT 2fH 168AH: Get Vendor-Specific DPMI API Entry Address