i386/i386.reference/SUB.htm

   1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
   2 <HTML>
   3 <HEAD>
   4 <TITLE>80386 Programmer's Reference Manual -- Opcode SUB</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="STR.htm"> STR Store Task Register</A><BR>
  10 <B>next:</B><A HREF="TEST.htm"> TEST Logical Compare</A>
  11 <P>
  12 <HR>
  13 <P>
  14 <H1>SUB -- Integer Subtraction</H1>
  15
  16 <PRE>
  17 Opcode      Instruction      Clocks   Description
  18
  19 2C  ib      SUB AL,imm8      2        Subtract immediate byte from AL
  20 2D  iw      SUB AX,imm16     2        Subtract immediate word from AX
  21 2D  id      SUB EAX,imm32    2        Subtract immediate dword from EAX
  22 80  /5 ib   SUB r/m8,imm8    2/7      Subtract immediate byte from r/m byte
  23 81  /5 iw   SUB r/m16,imm16  2/7      Subtract immediate word from r/m word
  24 81  /5 id   SUB r/m32,imm32  2/7      Subtract immediate dword from r/m
  25                                       dword
  26 83  /5 ib   SUB r/m16,imm8   2/7      Subtract sign-extended immediate byte
  27                                       from r/m word
  28 83  /5 ib   SUB r/m32,imm8   2/7      Subtract sign-extended immediate byte
  29                                       from r/m dword
  30 28  /r      SUB r/m8,r8      2/6      Subtract byte register from r/m byte
  31 29  /r      SUB r/m16,r16    2/6      Subtract word register from r/m word
  32 29  /r      SUB r/m32,r32    2/6      Subtract dword register from r/m
  33                                       dword
  34 2A  /r      SUB r8,r/m8      2/7      Subtract byte register from r/m byte
  35 2B  /r      SUB r16,r/m16    2/7      Subtract word register from r/m word
  36 2B  /r      SUB r32,r/m32    2/7      Subtract dword register from r/m
  37                                       dword
  38 </PRE>
  39
  40
  41 <H2>Operation</H2>
  42
  43 <PRE>
  44 IF SRC is a byte and DEST is a word or dword
  45 THEN DEST := DEST - SignExtend(SRC);
  46 ELSE DEST := DEST - SRC;
  47 FI;
  48 </PRE>
  49
  50 <H2>Description</H2>
  51
  52 SUB subtracts the second operand (SRC) from the first operand (DEST). The
  53 first operand is assigned the result of the subtraction, and the flags are
  54 set accordingly.
  55 <P>
  56 When an immediate byte value is subtracted from a word operand, the
  57 immediate value is first sign-extended to the size of the destination
  58 operand.
  59
  60 <H2>Flags Affected</H2>
  61
  62 OF, SF, ZF, AF, PF, and CF as described in <A HREF="appc.htm">Appendix C</A>
  63
  64 <H2>Protected Mode Exceptions</H2>
  65
  66 #GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal
  67 memory operand effective address in the CS, DS, ES, FS, or GS segments;
  68 #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page
  69 fault
  70
  71 <H2>Real Address Mode Exceptions</H2>
  72
  73 Interrupt 13 if any part of the operand would lie outside of the effective
  74 address space from 0 to 0FFFFH
  75
  76 <H2>Virtual 8086 Mode Exceptions</H2>
  77
  78 Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault
  79
  80
  81 <P>
  82 <HR>
  83 <P>
  84 <B>up:</B> <A HREF="c17.htm">
  85 Chapter 17 -- 80386 Instruction Set</A><BR>
  86 <B>prev:</B><A HREF="STR.htm"> STR Store Task Register</A><BR>
  87 <B>next:</B><A HREF="TEST.htm"> TEST Logical Compare</A>
  88 </BODY>