Specifications

Intel
®
64 and IA-32 Architectures Software Developer’s Manual Documentation Changes 180
Documentation Changes
Instruction Operand Encoding
...
SCAS/SCASB/SCASW/SCASD—Scan String
Opcode Instruction Op/
En
64-Bit
Mode
Compat/
Leg Mode
Description
1B /r SBB r32, r/m32 D Valid Valid Subtract with borrow r/m32
from r32.
REX.W + 1B /r SBB r64, r/m64 DValid N.E. Subtract with borrow r/m64
from r64.
NOTES:
* In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is
used: AH, BH, CH, DH.
Op/En Operand 1 Operand 2 Operand 3 Operand 4
A AL/AX/EAX/RAX imm8/16/32 NA NA
B ModRM:r/m (w) imm8/16/32 NA NA
C ModRM:r/m (w) ModRM:reg (r) NA NA
D ModRM:reg (w) ModRM:r/m (r) NA NA
Opcode Instruction Op/
En
64-Bit
Mode
Compat/
Leg Mode
Description
AE SCAS m8 A Valid Valid Compare AL with byte at
ES:(E)DI or RDI, then set
status flags.*
AF SCAS m16 A Valid Valid Compare AX with word at
ES:(E)DI or RDI, then set
status flags.*
AF SCAS m32 A Valid Valid Compare EAX with
doubleword at ES(E)DI or
RDI then set status flags.*
REX.W + AF SCAS m64 A Valid N.E. Compare RAX with
quadword at RDI or EDI then
set status flags.
AE SCASB A Valid Valid Compare AL with byte at
ES:(E)DI or RDI then set
status flags.*
AF SCASW A Valid Valid Compare AX with word at
ES:(E)DI or RDI then set
status flags.*
AF SCASD A Valid Valid Compare EAX with
doubleword at ES:(E)DI or
RDI then set status flags.*
REX.W + AF SCASQ A Valid N.E. Compare RAX with
quadword at RDI or EDI then
set status flags.