Instruction Set SUB
SUB -- Integer Subtraction
SUB -- Integer Subtraction
Opcode Instruction Clocks Description
2C ib SUB AL,imm8 2 Subtract immediate byte from AL
2D iw SUB AX,imm16 2 Subtract immediate word from AX
2D id SUB EAX,imm32 2 Subtract immediate dword from EAX
80 /5 ib SUB r/m8,imm8 2/7 Subtract immediate byte from r/m byte
81 /5 iw SUB r/m16,imm16 2/7 Subtract immediate word from r/m word
81 /5 id SUB r/m32,imm32 2/7 Subtract immediate dword from r/m
dword
83 /5 ib SUB r/m16,imm8 2/7 Subtract sign-extended immediate byte
from r/m word
83 /5 ib SUB r/m32,imm8 2/7 Subtract sign-extended immediate byte
from r/m dword
28 /r SUB r/m8,r8 2/6 Subtract byte register from r/m byte
29 /r SUB r/m16,r16 2/6 Subtract word register from r/m word
29 /r SUB r/m32,r32 2/6 Subtract dword register from r/m
dword
2A /r SUB r8,r/m8 2/7 Subtract byte register from r/m byte
2B /r SUB r16,r/m16 2/7 Subtract word register from r/m word
2B /r SUB r32,r/m32 2/7 Subtract dword register from r/m
dword
Operation
IF SRC is a byte and DEST is a word or dword
THEN DEST = DEST - SignExtend(SRC);
ELSE DEST = DEST - SRC;
FI;
Description
SUB subtracts the second operand (SRC) from the first operand (DEST). The
first operand is assigned the result of the subtraction, and the flags are
set accordingly.
When an immediate byte value is subtracted from a word operand, the
immediate value is first sign-extended to the size of the destination
operand.
Flags Affected
OF, SF, ZF, AF, PF, and CF as described in Appendix C
Protected Mode Exceptions
#GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal
memory operand effective address in the CS, DS, ES, FS, or GS segments;
#SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page
fault
Real Address Mode Exceptions
Interrupt 13 if any part of the operand would lie outside of the effective
address space from 0 to 0FFFFH
Virtual 8086 Mode Exceptions
Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault