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This HTML version of the file intel.doc from the
PC Game Programmer's guide was produced by Zack T Smith. Fancy HTML modifications are copyright ©
2005 by Zack T Smith, all rights reserved.
This information is provided in the hope that it will be useful,
but without any warranty. It is provided AS-IS,
without even the implied warranty of fitness for a particular purpose.
S Instructions
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.
Clocks Size
Operands 808x 286 386 486 Bytes
none 4 2 3 2 1
SAL/SHL - Shift Arithmetic Left / Shift Logical Left
Usage: SAL dest,count
SHL dest,count
Modifies flags: CF OF PF SF ZF (AF undefined)
+---+ +-----------------------+
| C |<--| 7 <---------------- 0 |<--0
+---+ +-----------------------+
Shifts the destination left by "count" bits with zeroes shifted
in on right. The Carry Flag contains the last bit shifted out.
Clocks Size
Operands 808x 286 386 486 Bytes
reg,1 2 2 3 3 2
mem,1 15+EA 7 7 4 2-4 (W88=23+EA)
reg,CL 8+4n 5+n 3 3 2
mem,CL 20+EA+4n 8+n 7 4 2-4 (W88=28+EA+4n)
reg,immed8 - 5+n 3 2 3
mem,immed8 - 8+n 7 4 3-5
SAR - Shift Arithmetic Right
Usage: SAR dest,count
Modifies flags: CF OF PF SF ZF (AF undefined)
+-----------------------+ +---+
+-->| 7 ----------------> 0 |-->| C |
| +-----------------------+ +---+
| |
+-----+
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg,1 2 2 3 3 2
mem,1 15+EA 7 7 4 2-4 (W88=23+EA)
reg,CL 8+4n 5+n 3 3 2
mem,CL 20+EA+4n 8+n 7 4 2-4 (W88=28+EA+4n)
reg,immed8 - 5+n 3 2 3
mem,immed8 - 8+n 7 4 3-5
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".
Clocks Size
Operands 808x 286 386 486 Bytes
reg,reg 3 2 2 1 2
mem,reg 16+EA 7 6 3 2-4 (W88=24+EA)
reg,mem 9+EA 7 7 2 2-4 (W88=13+EA)
reg,immed 4 3 2 1 3-4
mem,immed 17+EA 7 7 3 3-6 (W88=25+EA)
accum,immed 4 3 2 1 2-3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
string 15 7 7 6 1 (W88=19)
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
SETL/SETNGE - Set if Less / Set if Not Greater or Equal (386+)
Usage: SETL dest
SETNGE dest
(signed, 386+)
Modifies flags: none
Sets the byte in the operand to 1 if the Sign Flag is not equal
to the Overflow Flag, otherwise sets the operand to 0.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg8 - - 4 3 3
mem8 - - 5 4 3
SGDT - Store Global Descriptor Table (286+ privileged)
Usage: SGDT dest
Modifies flags: none
Stores the Global Descriptor Table (GDT) Register into the
specified operand.
Clocks Size
Operands 808x 286 386 486 Bytes
mem64 - 11 9 10 5
SIDT - Store Interrupt Descriptor Table (286+ privileged)
Usage: SIDT dest
Modifies flags: none
Stores the Interrupt Descriptor Table (IDT) Register into the
specified operand.
Clocks Size
Operands 808x 286 386 486 Bytes
mem64 - 12 9 10 5
SHL - Shift Logical Left
SHR - Shift Logical Right
Usage: SHR dest,count
Modifies flags: CF OF PF SF ZF (AF undefined)
+-----------------------+ +---+
0-->| 7 ----------------> 0 |-->| C |
+-----------------------+ +---+
Shifts the destination right by "count" bits with zeroes shifted
in on the left. The Carry Flag contains the last bit shifted out.
Clocks Size
Operands 808x 286 386 486 Bytes
reg,1 2 2 3 2
mem,1 15+EA 7 7 2-4 (W88=23+EA)
reg,CL 8+4n 5+n 3 2
mem,CL 20+EA+4n 8+n 7 2-4 (W88=28+EA+4n)
reg,immed8 - 5+n 3 3
mem,immed8 - 8+n 7 3-5
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg16,reg16,immed8 - - 3 2 4
reg32,reg32,immed8 - - 3 2 4
mem16,reg16,immed8 - - 7 3 6
mem32,reg32,immed8 - - 7 3 6
reg16,reg16,CL - - 3 3 3
reg32,reg32,CL - - 3 3 3
mem16,reg16,CL - - 7 4 5
mem32,reg32,CL - - 7 4 5
SLDT - Store Local Descriptor Table (286+ privileged)
Usage: SLDT dest
Modifies flags: none
Stores the Local Descriptor Table (LDT) Register into the
specified operand.
Clocks Size
Operands 808x 286 386 486 Bytes
reg16 - 2 2 2 3
mem16 - 2 2 3 5
SMSW - Store Machine Status Word (286+ privileged)
Usage: SMSW dest
Modifies flags: none
Store Machine Status Word (MSW) into "dest".
Clocks Size
Operands 808x 286 386 486 Bytes
reg16 - 2 10 2 3
mem16 - 3 3 3 5
STC - Set Carry
Usage: STC
Modifies flags: CF
Sets the Carry Flag to 1.
Clocks Size
Operands 808x 286 386 486 Bytes
none 2 2 2 2 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.
Clocks Size
Operands 808x 286 386 486 Bytes
none 2 2 2 2 1
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.
Clocks Size
Operands 808x 286 386 486 Bytes
none 2 2 2 5 1
STOS - Store String (Byte, Word or Doubleword)
Usage: STOS dest
STOSB
STOSW
STOSD
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.
Clocks Size
Operands 808x 286 386 486 Bytes
dest 11 3 4 5 1 (W88=15)
STR - Store Task Register (286+ privileged)
Usage: STR dest
Modifies flags: None
Stores the current Task Register to the specified operand.
Clocks Size
Operands 808x 286 386 486 Bytes
reg16 - 2 2 2 3
mem16 - 3 2 3 5
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.
Clocks Size
Operands 808x 286 386 486 Bytes
reg,reg 3 2 2 1 2
mem,reg 16+EA 7 6 3 2-4 (W88=24+EA)
reg,mem 9+EA 7 7 2 2-4 (W88=13+EA)
reg,immed 4 3 2 1 3-4
mem,immed 17+EA 7 7 3 3-6 (W88=25+EA)
accum,immed 4 3 2 1 2-3
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