i386/i386.reference/NEG.htm

   1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
   2 <HTML>
   3 <HEAD>
   4 <TITLE>80386 Programmer's Reference Manual -- Opcode NEG</TITLE>
   5 </HEAD>
   6 <BODY>
   7 <B>up:</B> <A HREF="c17.htm">
   8 Chapter 17 -- 80386 Instruction Set</A><BR>
   9 <B>prev:</B><A HREF="MUL.htm"> MUL Unsigned Multiplication of AL or AX</A><BR>
  10 <B>next:</B><A HREF="NOP.htm"> NOP No Operation</A>
  11 <P>
  12 <HR>
  13 <P>
  14 <H1>NEG -- Two's Complement Negation</H1>
  15
  16 <PRE>
  17 Opcode  Instruction   Clocks    Description
  18
  19 F6  /3  NEG r/m8      2/6       Two's complement negate r/m byte
  20 F7  /3  NEG r/m16     2/6       Two's complement negate r/m word
  21 F7  /3  NEG r/m32     2/6       Two's complement negate r/m dword
  22 </PRE>
  23
  24 <H2>Operation</H2>
  25
  26 <PRE>
  27 IF r/m = 0 THEN CF := 0 ELSE CF := 1; FI;
  28 r/m := - r/m;
  29 </PRE>
  30
  31 <H2>Description</H2>
  32
  33 NEG replaces the value of a register or memory operand with its two's
  34 complement. The operand is subtracted from zero, and the result is placed
  35 in the operand.
  36 <P>
  37 The carry flag is set to 1, unless the operand is zero, in which case the
  38 carry flag is cleared to 0.
  39
  40 <H2>Flags Affected</H2>
  41
  42 CF as described above; OF, SF, ZF, and PF as described in <A HREF="appc.htm">Appendix C</A>
  43
  44 <H2>Protected Mode Exceptions</H2>
  45
  46 #GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal
  47 memory operand effective address in the CS, DS, ES, FS, or GS
  48 segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)
  49 for a page fault
  50
  51 <H2>Real Address Mode Exceptions</H2>
  52
  53 Interrupt 13 if any part of the operand would lie outside of the effective
  54 address space from 0 to 0FFFFH
  55
  56 <H2>Virtual 8086 Mode Exceptions</H2>
  57
  58 Same exceptions as in real-address mode; #PF(fault-code) for a page
  59 fault
  60
  61
  62 <P>
  63 <HR>
  64 <P>
  65 <B>up:</B> <A HREF="c17.htm">
  66 Chapter 17 -- 80386 Instruction Set</A><BR>
  67 <B>prev:</B><A HREF="MUL.htm"> MUL Unsigned Multiplication of AL or AX</A><BR>
  68 <B>next:</B><A HREF="NOP.htm"> NOP No Operation</A>
  69 </BODY>