Intel Extensible Firmware Interface - Manual (Page 788)

Extensible Firmware Interface Specification
19-14 12/01/02 Version 1.10
ASHR
SYNTAX:
ASHR[32|64] {@}R
1
, {@}R
2
{Index16|Immed16}
DESCRIPTION:
Performs an arithmetic right-shift of a signed 32-bit (ASHR32) or 64-bit (ASHR64) operand and
stores the result back to Operand 1
OPERATION:
Operand 1 <= Operand 1 SHIFT-RIGHT Operand 2
Table 19-10 ASHR 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 = 0x19
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 Operand 2
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 and is
added to the register contents such that Operand 2 = R
2
+ Immed16.
• If the instruction is ASHR32, and Operand 1 is direct, then the result is stored back to the
Operand 1 register with the upper 32 bits cleared.