Instruction Set LEA
LEA -- Load Effective Address
LEA -- Load Effective Address
Opcode Instruction Clocks Description
8D /r LEA r16,m 2 Store effective address for m in register r16
8D /r LEA r32,m 2 Store effective address for m in register r32
8D /r LEA r16,m 2 Store effective address for m in register r16
8D /r LEA r32,m 2 Store effective address for m in register r32
Operation
IF 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;
Description
LEA 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
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Flags Affected
None
Protected Mode Exceptions
#UD if the second operand is a register
Real Address Mode Exceptions
Interrupt 6 if the second operand is a register
Virtual 8086 Mode Exceptions
Same exceptions as in Real Address Mode