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THE
80286
INSTRUCTION SET
BOUND-Check
Array
Index
Against
Bounds
Opcode Instruction Clocks
Description
62.
/r
BOUND
rw,md
noj=13
INT 5
if
rw not within bounds
FLAGS MODIFIED
None
FLAGS UNDEFINED
None
OPERATION
BOUND
is
used
to
ensure that a signed array index
is
within the limits defined
by
a two-word block
of memory. The
first operand (a register)
tnustbe
greater than or equal to the first word
in
memory,
and
·less than or equal
to
the second word
in
memory.
If
the register
is
not within the bounds, an
INTERRUPT
5 occurs. .
The two-word block might typically be found just before the array itself and therefore
would
be acces-
sible
at
a constant offset of
-4
from the array, simplifying the addressing.
PROTECTED MODE EXCEPTIONS.
INTERRUPT
5 if the bounds test fails, as described above.
#GP(O)
for
an illegal memory operand
effective address in the C8, D8, or
E8
segments; #88(0) for an illegal address
in
the
88
segment.
The second operand must be a memory operand, not a register.
If
the BOUND instruction
is
executed
with a ModRM
byte representing a register second operand, then fault #UD will
occUr.
REAL ADDRESS MODE EXCEPTIONS
INTERRUPT
5 if the bounds test fails, as described above. Interrupt
13
for
a second operand
at
offset
OFFFDH or higher. Interrupt 6 if the second operand
is
a register,as described in the paragraph above.
B-22