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BASIC EXECUTION ENVIRONMENT

Table 3-4. Effective Operandand Address-Size Attributes in 64-Bit Mode

L Flag in Code Segment

 

 

 

 

 

 

 

 

Descriptor

1

1

1

1

1

1

1

1

 

 

 

 

 

 

 

 

 

REX.W Prefix

0

0

0

0

1

1

1

1

 

 

 

 

 

 

 

 

 

Operand-Size Prefix 66H

N

N

Y

Y

N

N

Y

Y

 

 

 

 

 

 

 

 

 

Address-Size Prefix 67H

N

Y

N

Y

N

Y

N

Y

 

 

 

 

 

 

 

 

 

Effective Operand Size

32

32

16

16

64

64

64

64

 

 

 

 

 

 

 

 

 

Effective Address Size

64

32

64

32

64

32

64

32

 

 

 

 

 

 

 

 

 

NOTES:

 

 

 

 

 

 

 

 

Y: Yes - this instruction prefix is present.

N: No - this instruction prefix is not present.

3.7OPERAND ADDRESSING

IA-32 machine-instructions act on zero or more operands. Some operands are specified explicitly and others are implicit. The data for a source operand can be located in:

the instruction itself (an immediate operand) a register

a memory location an I/O port

When an instruction returns data to a destination operand, it can be returned to:

a register

a memory location an I/O port

3.7.1Immediate Operands

Some instructions use data encoded in the instruction itself as a source operand. These operands are called immediate operands (or simply immediates). For example, the following ADD instruction adds an immediate value of 14 to the contents of the EAX register:

ADD EAX, 14

All arithmetic instructions (except the DIV and IDIV instructions) allow the source operand to be an immediate value. The maximum value allowed for an immediate operand varies among instructions, but can never be greater than the maximum value of an unsigned doubleword integer (232).

3-26 Vol. 1

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