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80386 Programmer's Reference Manual -- Opcode LEA |
LEA -- Load Effective Address
OperationIF OperandSize = 16 AND AddressSize = 16 THEN r16 := Addr(m); ELSE IF OperandSize = 16 AND AddressSize = 32 THEN r16 := Truncate_to_16bits(Addr(m)); (* 32-bit address *) ELSE IF OperandSize = 32 AND AddressSize = 16 THEN r32 := Truncate_to_16bits(Addr(m)); ELSE IF OperandSize = 32 AND AddressSize = 32 THEN r32 := Addr(m); FI; FI; FI; FI; DescriptionLEA calculates the effective address (offset part) and stores it in the specified register. The operand-size attribute of the instruction (represented by OperandSize in the algorithm under "Operation" above) is determined by the chosen register. The address-size attribute (represented by AddressSize) is determined by the USE attribute of the segment containing the second operand. The address-size and operand-size attributes affect the action performed by LEA, as follows:Operand Size Address Size Action Performed 16 16 16-bit effective address is calculated and stored in requested 16-bit register destination. 16 32 32-bit effective address is calculated. The lower 16 bits of the address are stored in the requested 16-bit register destination. 32 16 16-bit effective address is calculated. The 16-bit address is zero-extended and stored in the requested 32-bit register destination. 32 32 32-bit effective address is calculated and stored in the requested 32-bit register destination. Flags AffectedNoneProtected Mode Exceptions#UD if the second operand is a registerReal Address Mode ExceptionsInterrupt 6 if the second operand is a registerVirtual 8086 Mode ExceptionsSame exceptions as in Real Address Mode
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