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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Opcode DEC</TITLE></HEAD><BODY><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="DAS.htm"> DAS Decimal Adjust AL after Subtraction</A><BR><B>next:</B><A HREF="DIV.htm"> DIV Unsigned Divide</A> <P><HR><P><H1>DEC -- Decrement by 1</H1><PRE>Opcode Instruction Clocks DescriptionFE /1 DEC r/m8 2/6 Decrement r/m byte by 1FF /1 DEC r/m16 2/6 Decrement r/m word by 1 DEC r/m32 2/6 Decrement r/m dword by 148+rw DEC r16 2 Decrement word register by 148+rw DEC r32 2 Decrement dword register by 1</PRE><H2>Operation</H2><PRE>DEST := DEST - 1;</PRE><H2>Description</H2>DEC subtracts 1 from the operand. DEC does not change the carry flag.To affect the carry flag, use the <A HREF="SUB.htm">SUB</A> instruction with an immediateoperand of 1.<H2>Flags Affected</H2>OF, SF, ZF, AF, and PF as described in <A HREF="appc.htm">Appendix C</A>.<H2>Protected Mode Exceptions</H2>#GP(0) if the result is a nonwritable segment; #GP(0) for an illegalmemory operand effective address in the CS, DS, ES, FS, or GSsegments; #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 effectiveaddress space from 0 to 0FFFFH<H2>Virtual 8086 Mode Exceptions</H2>Same exceptions as in Real Address Mode; #PF(fault-code) for a pagefault<P><HR><P><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="DAS.htm"> DAS Decimal Adjust AL after Subtraction</A><BR><B>next:</B><A HREF="DIV.htm"> DIV Unsigned Divide</A> </BODY>⌨️ 快捷键说明
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