hw/i386.reference/SBB.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode SBB</TITLE>
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   8 Chapter 17 -- 80386 Instruction Set</A><BR>
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  13 <P>
  14 <H1>SBB -- Integer Subtraction with Borrow</H1>
  15
  16
  17 <PRE>
  18 Opcode       Instruction       Clocks  Description
  19
  20 1C  ib       SBB AL,imm8       2       Subtract with borrow immediate byte
  21                                        from AL
  22 1D  iw       SBB AX,imm16      2       Subtract with borrow immediate word
  23                                        from AX
  24 1D  id       SBB EAX,imm32     2       Subtract with borrow immediate
  25                                        dword from EAX
  26 80  /3 ib    SBB r/m8,imm8     2/7     Subtract with borrow immediate byte
  27                                        from r/m byte
  28 81  /3 iw    SBB r/m16,imm16   2/7     Subtract with borrow immediate word
  29                                        from r/m word
  30 81  /3 id    SBB r/m32,imm32   2/7     Subtract with borrow immediate
  31                                        dword from r/m dword
  32 83  /3 ib    SBB r/m16,imm8    2/7     Subtract with borrow sign-extended
  33                                        immediate byte from r/m word
  34 83  /3 ib    SBB r/m32,imm8    2/7     Subtract with borrow sign-extended
  35                                        immediate byte from r/m dword
  36 18  /r       SBB r/m8,r8       2/6     Subtract with borrow byte register
  37                                        from r/m byte
  38 19  /r       SBB r/m16,r16     2/6     Subtract with borrow word register
  39                                        from r/m word
  40 19  /r       SBB r/m32,r32     2/6     Subtract with borrow dword register
  41                                        from r/m dword
  42 1A  /r       SBB r8,r/m8       2/7     Subtract with borrow byte register
  43                                        from r/m byte
  44 1B  /r       SBB r16,r/m16     2/7     Subtract with borrow word register
  45                                        from r/m word
  46 1B  /r       SBB r32,r/m32     2/7     Subtract with borrow dword register
  47                                        from r/m dword
  48 </PRE>
  49
  50 <H2>Operation</H2>
  51
  52 <PRE>
  53 IF SRC is a byte and DEST is a word or dword
  54 THEN DEST := DEST - (SignExtend(SRC) + CF)
  55 ELSE DEST := DEST - (SRC + CF);
  56 </PRE>
  57
  58 <H2>Description</H2>
  59
  60 SBB adds the second operand (DEST) to the carry flag (CF) and
  61 subtracts the result from the first operand (SRC). The result of the
  62 subtraction is assigned to the first operand (DEST), and the flags are
  63 set accordingly.
  64 <P>
  65 When an immediate byte value is subtracted from a word operand, the
  66 immediate value is first sign-extended.
  67
  68 <H2>Flags Affected</H2>
  69
  70 OF, SF, ZF, AF, PF, and CF as described in <A HREF="appc.htm">Appendix C</A>
  71
  72 <H2>Protected Mode Exceptions</H2>
  73
  74 #GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal
  75 memory operand effective address in the CS, DS, ES, FS, or GS
  76 segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)
  77 for a page fault
  78
  79 <H2>Real Address Mode Exceptions</H2>
  80
  81 Interrupt 13 if any part of the operand would lie outside of the effective
  82 address space from 0 to 0FFFFH
  83
  84 <H2>Virtual 8086 Mode Exceptions</H2>
  85
  86 Same exceptions as in Real Address Mode; #PF(fault-code) for a page
  87 fault
  88
  89
  90 <P>
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  93 <B>up:</B> <A HREF="c17.htm">
  94 Chapter 17 -- 80386 Instruction Set</A><BR>
  95 <B>prev:</B><A HREF="SAL.htm"> SAL/SAR/SHL/SHR Shift Instructions</A><BR>
  96 <B>next:</B><A HREF="SCAS.htm"> SCAS/SCASB/SCASW/SCASD Compare String Data</A>
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