!
!                       E MACHINE OPERAND FORMS
!                       -----------------------
!
! Simple Forms
! ------------
!
! Litval
! corresponding address none (but see note A)
!
!               The operand is a literal
!
! Regval& Fregval  (also Regaddr & Regvar)
! corresponding address forms:-  none (but see note A)
!
!               The operand is in a Register - the form Regaddr
!               is used when the operand is known to be an
!               address but for code generation there is no
!               difference.  Care must be taken with Regvar
!               not to overwrite it except at assignment
!
! Dirval (also Constval,TempVal,Diraddr & Tempaddr)
! corresponding address forms:- AddrDir, AddrConst and AddrDir.
!
!               The operand is at a known offset in an E-machine
!               area.  Constval implies Constant (read only) -
!               TempVal implies local stack frame and single use
!               so libraries can be taken like increment in situ.
!               The forms Diraddr & Tempaddr are used when the
!               location is known to contain an address but for
!               code generation there are no differences.

!
!
! Indirect Forms
! --------------
!
! IndDirVal, IndTempVal and IndRegVal
! corresponding address forms:-  DirVal, TempVal & Regaddr
!
!               There is a pointer to the item in an E-machine and
!               (or register).  Pointers are 32 bit items.
!
! Modified Forms
! --------------
!
! IndRegModVal
! Corresponding address form:-  RegModAddr
!
!              The operand is somewhere in store;  its address is
!              computed by incrementing the register by a modifier
!              - not always a literal.  Used for array elements and
!              items in mapped records.
!
! Ind DirModVal and IndTempModVal
! corresponding address forms:-  DirModAddr and TempModAddr
!
!              The operand is anywhere in store;  its address is
!              computed by loading a base pointer from an E-machine
!              area (or temparray) and adding a modifier.  Items in
!              IMP and Pascal global stack frames are accessed thus;
!              in these cases the modifier is a literal.  Also dynamic
!              arrays are via this mechanism.
!
! AddrDirModVal
! corresponding address form:-  AddrDirMod
!
!              The operand is part of an array with fixed bounds in
!              an E-machine area.  The first item (A(O)) is specified
!              together with a modifier.  The address of the item is
!              the address of the base incremented by a modifier -
!              optimisations are possible for constant modifiers.
!
!
! NOTES
! -----
!
!   A)   Certain forms which do not logically have an address are given one
!        by storing the value in a temporary; this is for Fortran but should
!        not be part of the E-machine.  Fortran should do this at a higher
!        level.
!
!   B)   Where there is hardware assistance for a display it is desirable
!        for display items to be distinguished from array access.  Here
!        IndDispModVal and DispModAddr are used.  Logically the same
!        as IndDirModVal (etc).
!