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     See also: Scaling (ss) Field, Index Field,
               Base Register (base) Field, Register/Memory (r/m) Field
 
     Many 80386/486 extended memory operands are too complex to be
     represented by a single mod-reg-r/m byte. For these operands, a
     value of 100 in the r/m field signals the presence of a second
     encoding byte called the Scaled Index Base (SIB) byte.
 
     The SIB byte is made up of the following fields:
 
     Field     Bits
 
     base      0-2
     index     3-5
     ss        6-7
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