i386/i386.reference/BOUND.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Opcode BOUND</TITLE>
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  14 <H1>BOUND -- Check Array Index Against Bounds</H1>
  15
  16 <PRE>
  17 Opcode    Instruction          Clocks    Description
  18
  19 62 /r     BOUND r16,m16&16     10        Check if r16 is within bounds
  20                                          (passes test)
  21 62 /r     BOUND r32,m32&32     10        Check if r32 is within bounds
  22                                          (passes test)
  23 </PRE>
  24
  25 <H2>Operation</H2>
  26
  27 <PRE>
  28 IF (LeftSRC < [RightSRC] OR LeftSRC > [RightSRC + OperandSize/8])
  29    (* Under lower bound or over upper bound *)
  30 THEN Interrupt 5;
  31 FI;
  32 </PRE>
  33
  34 <H2>Description</H2>
  35
  36 BOUND ensures that a signed array index is within the limits specified by a
  37 block of memory consisting of an upper and a lower bound. Each bound uses
  38 one word for an operand-size attribute of 16 bits and a doubleword for an
  39 operand-size attribute of 32 bits. The first operand (a register) must be
  40 greater than or equal to the first bound in memory (lower bound), and less
  41 than or equal to the second bound in memory (upper bound). If the register
  42 is not within bounds, an Interrupt 5 occurs; the return EIP points to the
  43 BOUND instruction.
  44 <P>
  45 The bounds limit data structure is usually placed just before the array
  46 itself, making the limits addressable via a constant offset from the
  47 beginning of the array.
  48
  49 <H2>Flags Affected</H2>
  50
  51 None
  52
  53 <H2>Protected Mode Exceptions</H2>
  54
  55 Interrupt 5 if the bounds test fails, as described above; #GP(0) for an
  56 illegal memory operand effective address in the CS, DS, ES, FS, or GS
  57 segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)
  58 for a page fault
  59 <P>
  60 The second operand must be a memory operand, not a register. If BOUND is
  61 executed with a ModRM byte representing a register as the second operand,
  62 #UD occurs.
  63
  64 <H2>Real Address Mode Exceptions</H2>
  65
  66 Interrupt 5 if the bounds test fails; Interrupt 13 if any part of the
  67 operand would lie outside of the effective address space from 0 to 0FFFFH;
  68 Interrupt 6 if the second operand is a register
  69
  70 <H2>Virtual 8086 Mode Exceptions</H2>
  71
  72 Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault
  73
  74
  75 <P>
  76 <HR>
  77 <P>
  78 <B>up:</B> <A HREF="c17.htm">
  79 Chapter 17 -- 80386 Instruction Set</A><BR>
  80 <B>prev:</B><A HREF="ARPL.htm"> ARPL Adjust RPL Field of Selector</A><BR>
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