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SUB.htm
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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HTML>
<HEAD>
<TITLE>80386 Programmer's Reference Manual -- Opcode SUB</TITLE>
</HEAD>
<BODY>
<B>up:</B> <A HREF="c17.htm">
Chapter 17 -- 80386 Instruction Set</A><BR>
<B>prev:</B><A HREF="STR.htm"> STR Store Task Register</A><BR>
<B>next:</B><A HREF="TEST.htm"> TEST Logical Compare</A>
<P>
<HR>
<P>
<H1>SUB -- Integer Subtraction</H1>
<PRE>
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 r/m byte from byte register
2B /r SUB r16,r/m16 2/7 Subtract r/m word from word register
2B /r SUB r32,r/m32 2/7 Subtract r/m dword from dword
register
</PRE>
<H2>Operation</H2>
<PRE>
IF SRC is a byte and DEST is a word or dword
THEN DEST := DEST - SignExtend(SRC);
ELSE DEST := DEST - SRC;
FI;
</PRE>
<H2>Description</H2>
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.
<P>
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.
<H2>Flags Affected</H2>
OF, SF, ZF, AF, PF, and CF as described in <A HREF="appc.htm">Appendix C</A>
<H2>Protected Mode Exceptions</H2>
#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
<H2>Real Address Mode Exceptions</H2>
Interrupt 13 if any part of the operand would lie outside of the effective
address space from 0 to 0FFFFH
<H2>Virtual 8086 Mode Exceptions</H2>
Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault
<P>
<HR>
<P>
<B>up:</B> <A HREF="c17.htm">
Chapter 17 -- 80386 Instruction Set</A><BR>
<B>prev:</B><A HREF="STR.htm"> STR Store Task Register</A><BR>
<B>next:</B><A HREF="TEST.htm"> TEST Logical Compare</A>
</BODY>