Intel Extensible Firmware Interface - Manual (Page 802)

Extensible Firmware Interface Specification
19-28 12/01/02 Version 1.10
EXTNDW
SYNTAX:
EXTNDW[32|64] {@}R
1
, {@}R
2
{Index16|Immed16}
DESCRIPTION:
Sign-extend a 16-bit Operand 2 value and store the result back to Operand 1. The value can be
signed extended to 32 bits (EXTNDW32) or 64 bits (EXTNDW64).
OPERATION:
Operand 1 <= (sign extended) Operand 2
Table 19-20. EXTNDW Instruction Encoding
BYTE DESCRIPTION
Bit Description
7 0 = Immediate/index absent
1 = Immediate/index present
6 0 = 32-bit operation
1 = 64-bit operation
0
0..5 Opcode = 0x1B
Bit Description
7 0 = Operand 2 direct
1 = Operand 2 indirect
4..6 Operand 2
3 0 = Operand 1 direct
1 = Operand 1 indirect
1
0..2 Operand 1
2..3 Optional 16-bit immediate data/index
BEHAVIORS AND RESTRICTIONS:
• If Operand 2 is indirect, then the immediate data is interpreted as an index, and the word value
is fetched from memory as a signed value at address [R
2
+ Index16].
• If Operand 2 is direct, then the immediate data is considered a signed immediate value such that
Operand 2 = R
2
+ Immed16, and the value is sign extended to 32 or 64 bits accordingly.
• If the instruction is EXTNDW32 and Operand 1 is direct, then the 32-bit result is stored in the
Operand 1 register with the upper 32 bits cleared.