The Compatibility Region Mapping Algorithm (also referred to as the thunking algorithm) is used by thunking code to convert 16:16 addresses to 0:32 addresses and vice versa.

This is achieved by ensuring LDT selectors have their limits set to 64K so that they tile the compatibility region (0M to 448M). This gives an easy conversion algorithm from the selector:offset address to the 32-bit linear address. In C language syntax this is expressed as follows:

linear_address=((selector >> 3) << 16) + offset

selector:offset=((linear_address. >> 13) | 7):(linear_address & 0x0000ffff)

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