SAHF - Store AH Register into FLAGS

Usage: SAHF

Modifies Flags: AF CF PF SF ZF

Transfers bits 0-7 of AH into the Flags Register. This includes AF, CF, PF, SF and ZF.

SAL/SHL - Shift Arithmetic Left / Shift Logical Left

Usage: SAL dest,count
SHL dest,count

Modifies Flags: CF OF PF SF ZF (AF undefined)



Shifts the destination left by "count" bits with zeroes shifted in on right. The Carry Flag contains the last bit shifted out.

SAR - Shift Arithmetic Right

Usage: SAR dest,count

Modifies Flags: CF OF PF SF ZF (AF undefined)



Shifts the destination right by "count" bits with the current sign bit replicated in the leftmost bit. The Carry Flag contains the last bit shifted out.

SBB - Subtract with Borrow/Carry

Usage: SBB dest,src

Modifies Flags: AF CF OF PF SF ZF

Subtracts the source from the destination, and subtracts 1 extra if the Carry Flag is set. Results are returned in "dest".

SCAS - Scan String (Byte, Word or Doubleword)

Usage: SCAS string
SCASB
SCASW
SCASD (386+)

Modifies Flags: AF CF OF PF SF ZF

Compares value at ES:DI (even if operand is specified) from the accumulator and sets the flags similar to a subtraction. DI is incremented/decremented based on the instruction format (or operand size) and the state of the Direction Flag. Use with REP prefixes.

SETAE/SETNB - Set if Above or Equal / Set if Not Below (386+)

Usage: SETAE dest
SETNB dest (unsigned, 386+)

Modifies Flags: None

Sets the byte in the operand to 1 if the Carry Flag is clear otherwise sets the operand to 0.

SETB/SETNAE - Set if Below / Set if Not Above or Equal (386+)

Usage: SETB dest
SETNAE dest (unsigned, 386+)

Modifies Flags: None

Sets the byte in the operand to 1 if the Carry Flag is set otherwise sets the operand to 0.

SETBE/SETNA - Set if Below or Equal / Set if Not Above (386+)

Usage: SETBE dest
SETNA dest (unsigned, 386+)

Modifies Flags: None

Sets the byte in the operand to 1 if the Carry Flag or the Zero Flag is set, otherwise sets the operand to 0.

SETE/SETZ - Set if Equal / Set if Zero (386+)

Usage: SETE dest
SETZ dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Zero Flag is set, otherwise sets the operand to 0.

SETNE/SETNZ - Set if Not Equal / Set if Not Zero (386+)

Usage: SETNE dest
SETNZ dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Zero Flag is clear, otherwise sets the operand to 0.

SETL/SETNGE - Set if Less / Set if Not Greater or Equal (386+)

Usage: SETL dest
SETNGE dest (signed, 386+)

Modifies Flags: None

SETGE/SETNL - Set if Greater or Equal / Set if Not Less (386+)

Usage: SETGE dest
SETNL dest (signed, 386+)

Modifies Flags: None

Sets the byte in the operand to 1 if the Sign Flag equals the Overflow Flag, otherwise sets the operand to 0.

SETLE/SETNG - Set if Less or Equal / Set if Not greater or Equal (386+)

Usage: SETLE dest
SETNG dest (signed, 386+)

Modifies Flags: None

Sets the byte in the operand to 1 if the Zero Flag is set or the Sign Flag is not equal to the Overflow Flag, otherwise sets the operand to 0.

SETG/SETNLE - Set if Greater / Set if Not Less or Equal (386+)

Usage: SETG dest
SETNLE dest (signed, 386+)

Modifies Flags: None

Sets the byte in the operand to 1 if the Zero Flag is clear or the Sign Flag equals to the Overflow Flag, otherwise sets the operand to 0.

SETS - Set if Signed (386+)

Usage: SETS dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Sign Flag is set, otherwise sets the operand to 0.

SETNS - Set if Not Signed (386+)

Usage: SETNS dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Sign Flag is clear, otherwise sets the operand to 0.

SETC - Set if Carry (386+)

Usage: SETC dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Carry Flag is set, otherwise sets the operand to 0.

SETNC - Set if Not Carry (386+)

Usage: SETNC dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Carry Flag is clear, otherwise sets the operand to 0.

SETO - Set if Overflow (386+)

Usage: SETO dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Overflow Flag is set, otherwise sets the operand to 0.

SETNO - Set if Not Overflow (386+)

Usage: SETNO dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Overflow Flag is clear, otherwise sets the operand to 0.

SETP/SETPE - Set if Parity / Set if Parity Even (386+)

Usage: SETP dest
SETPE dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Parity Flag is set, otherwise sets the operand to 0.

SETNP/SETPO - Set if No Parity / Set if Parity Odd (386+)

Usage: SETNP dest
SETPO dest

Modifies Flags: None

Sets the byte in the operand to 1 if the Parity Flag is clear, otherwise sets the operand to 0.

SGDT - Store Global Descriptor Table (286+ privileged)

Usage: SGDT dest

Modifies Flags: None

Stores the Global Descriptor Table (GDT) Register into the specified operand.

SIDT - Store Interrupt Descriptor Table (286+ privileged)

Usage: SIDT dest

Modifies Flags: None

Stores the Interrupt Descriptor Table (IDT) Register into the specified operand.

SHR - Shift Logical Right

Usage: SHR dest,count

Modifies Flags: CF OF PF SF ZF (AF undefined)



Shifts the destination right by "count" bits with zeroes shifted in on the left. The Carry Flag contains the last bit shifted out.

SHLD/SHRD - Double Precision Shift (386+)

Usage: SHLD dest,src,count
SHRD dest,src,count

Modifies Flags: CF PF SF ZF (OF,AF undefined)

SHLD shifts "dest" to the left "count" times and the bit positions opened are filled with the most significant bits of "src". SHRD shifts "dest" to the right "count" times and the bit positions opened are filled with the least significant bits of the second operand. Only the 5 lower bits of "count" are used.

SLDT - Store Local Descriptor Table (286+ privileged)

Usage: SLDT dest

Modifies Flags: none

Stores the Local Descriptor Table (LDT) Register into the specified operand.

SMSW - Store Machine Status Word (286+ privileged)

Usage: SMSW dest

Modifies Flags: none

Store Machine Status Word (MSW) into "dest".

STC - Set Carry

Usage: STC

Modifies Flags: CF

Sets the Carry Flag to 1.

STD - Set Direction Flag

Usage: STD

Modifies Flags: DF

Sets the Direction Flag to 1 causing string instructions to auto-decrement SI and DI instead of auto-increment.

STI - Set Interrupt Flag (Enable Interrupts)

Usage: STI

Modifies Flags: IF

Sets the Interrupt Flag to 1, which enables recognition of all hardware interrupts. If an interrupt is generated by a hardware device, an End of Interrupt (EOI) must also be issued to enable other hardware interrupts of the same or lower priority.

STOS - Store String (Byte, Word or Doubleword)

Usage: STOS dest
STOSB dest
STOSW dest
STOSD dest

Modifies Flags: none

Stores value in accumulator to location at ES:(E)DI (even if operand is given). (E)DI is incremented/decremented based on the size of the operand (or instruction format) and the state of the Direction Flag. Use with REP prefixes.

STR - Store Task Register (286+ privileged)

Usage: STR dest

Modifies Flags: None

Stores the current Task Register to the specified operand.

SUB - Subtract

Usage: SUB dest,src

Modifies Flags: AF CF OF PF SF ZF

The source is subtracted from the destination and the result is stored in the destination.

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