Intel 253666-024US - Manual (Page 112)

3-66 Vol. 2A BOUND—Check Array Index Against Bounds
INSTRUCTION SET REFERENCE, A-M
BOUND—Check Array Index Against Bounds
Description
BOUND determines if the first operand (array index) is within the bounds of an array
specified the second operand (bounds operand). The array index is a signed integer
located in a register. The bounds operand is a memory location that contains a pair of
signed doubleword-integers (when the operand-size attribute is 32) or a pair of
signed word-integers (when the operand-size attribute is 16). The first doubleword
(or word) is the lower bound of the array and the second doubleword (or word) is the
upper bound of the array. The array index must be greater than or equal to the lower
bound and less than or equal to the upper bound plus the operand size in bytes. If the
index is not within bounds, a BOUND range exceeded exception (#BR) is signaled.
When this exception is generated, the saved return instruction pointer points to the
BOUND instruction.
The bounds limit data structure (two words or doublewords containing the lower and
upper limits of the array) is usually placed just before the array itself, making the
limits addressable via a constant offset from the beginning of the array. Because the
address of the array already will be present in a register, this practice avoids extra
bus cycles to obtain the effective address of the array bounds.
This instruction executes as described in compatibility mode and legacy mode. It is
not valid in 64-bit mode.
Operation
IF 64bit Mode
THEN
#UD;
ELSE
IF (ArrayIndex < LowerBound OR ArrayIndex > UpperBound)
(* Below lower bound or above upper bound *)
THEN #BR; FI;
FI;
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
62 /r BOUND r16, m16&16 Invalid Valid Check if r16 (array index) is
within bounds specified by
m16&16.
62 /r BOUND r32, m32&32 Invalid Valid Check if r32 (array index) is
within bounds specified by
m16&16.