3-627
INSTRUCTION SET REFERENCE
SBBInteger Subtraction with Borrow
Description
This instruction adds the source operand (second operand) and the carry (CF) flag, and subtracts
the result from the destination operand (first operand). The result of the subtraction is stored in
the destination operand. The destination operand can be a register or a memory location; the
source operand can be an immediate, a register, or a memory location. (However, two memory
operands cannot be used in one instruction.) The state of the CF flag represents a borrow from
a previous subtraction.
When an immediate value is used as an operand, it is sign-extended to the length of the destina-
tion operand format.
The SBB instruction does not distinguish between signed or unsigned operands. Instead, the
processor evaluates the result for both data types and sets the OF and CF flags to indicate a
borrow in the signed or unsigned result, respectively. The SF flag indicates the sign of the signed
result.
The SBB instruction is usually executed as part of a multibyte or multiword subtraction in which
a SUB instruction is followed by a SBB instruction.
Operation
DEST
<
DEST (SRC + CF);
Flags Affected
The OF, SF, ZF, AF, PF, and CF flags are set according to the result.
Opcode
Instruction
Description
1C ib
SBB AL,imm8
Subtract with borrow imm8 from AL
1D iw
SBB AX,imm16
Subtract with borrow imm16 from AX
1D id
SBB EAX,imm32
Subtract with borrow imm32 from EAX
80 /3 ib
SBB r/m8,imm8
Subtract with borrow imm8 from r/m8
81 /3 iw
SBB r/m16,imm16
Subtract with borrow imm16 from r/m16
81 /3 id
SBB r/m32,imm32
Subtract with borrow imm32 from r/m32
83 /3 ib
SBB r/m16,imm8
Subtract with borrow sign-extended imm8 from r/m16
83 /3 ib
SBB r/m32,imm8
Subtract with borrow sign-extended imm8 from r/m32
18 /r
SBB r/m8,r8
Subtract with borrow r8 from r/m8
19 /r
SBB r/m16,r16
Subtract with borrow r16 from r/m16
19 /r
SBB r/m32,r32
Subtract with borrow r32 from r/m32
1A /r
SBB r8,r/m8
Subtract with borrow r/m8 from r8
1B /r
SBB r16,r/m16
Subtract with borrow r/m16 from r16
1B /r
SBB r32,r/m32
Subtract with borrow r/m32 from r32
