Hardware Reference
In-Depth Information
16.
How many registers does the machine whose instruction formats are given in Fig. 5-24
have?
17.
In Fig. 5-24, bit 23 is used to distinguish the use of format 1 from format 2. No bit is
provided to distinguish the use of format 3. How does the hardware know to use it?
18.
It is common in programming for a program to need to determine where a variable
X
is
with respect to the interval
A
to
B
. If a three-address instruction were available with
operands
A
,
B
, and
X
, how many condition code bits would have to be set by this in-
struction?
19.
Describe one advantage and one disadvantage of program-counter-relative addressing.
20.
The Core i7 has a condition code bit that keeps track of the carry out of bit 3 after an
arithmetic operation. What good is it?
21.
One of your friends has just come bursting into your room at 3
A.M.
, out of breath, to
tell you about his brilliant new idea: an instruction with two opcodes. Should you send
your friend off to the patent office or back to the drawing board?
22.
Tests of the form
if (k == 0) ...
if (a > b) ...
if (k < 5) ...
are common in programming. Devise an instruction to perform these tests efficiently.
What fields are present in your instruction?
23.
For the 16-bit binary number 1001 0101 1100 0011, show the effect of:
a. A right shift of 4 bits with zero fill.
b. A right shift of 4 bits with sign extension.
c. A left shift of 4 bits.
d. A left rotate of 4 bits.
e. A right rotate of 4 bits.
24.
How can you clear a memory word on a machine with no
CLR
instruction?
25.
Compute the Boolean expression (
A
AND
B
)OR
C
for
A = 1101 0000 1010 0011
B = 1111 1111 0000 1111
C = 0000 0000 0010 0000
26.
Devise a way to interchange two variables
A
and
B
without using a third variable or
register.
Hint
: Think about the
EXCLUSIVE OR
instruction.
27.
On a certain computer it is possible to move a number from one register to another,
shift each of them left by different amounts, and add the results in less time than a mul-
tiplication takes. Under what condition is this instruction sequence useful for comput-
ing ''constant
variable''?
28.
Different machines have different instruction densities (number of bytes required to
perform a certain computation). For the following Java code fragments, translate each
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