ECE 2035
Programming HW/SW Systems
4 problems, 5 pages
Exam Three
Fall 2014
19 November 2014
Instructions: This is a closed book, closed note exam. Calculators are not permitted. If you have
a question, raise your hand and I will come to you. Please work the exam in pencil and do not
separate the pages of the exam. For maximum credit, show your work.
Good Luck!
Your Name (please print) ________________________________________________
This exam will be conducted according to the Georgia Tech Honor Code. I pledge to neither give
nor receive unauthorized assistance on this exam and to abide by all provisions of the Honor
Code.
Signed ________________________________________________
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25
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25
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100
ECE 2035
Programming HW/SW Systems
4 problems, 5 pages
Exam Three
Fall 2014
19 November 2014
Problem 1 (25 points)
Hash Tables
Consider an open hash table composed of a four-bucket table, with each bucket containing a
variable length list. Each list entry has three slots <key, value, next> corresponding to the three
word groupings in the entries section. The hash function is key mod four. Inserted entries
are appended to the end of a bucket list. The initial state of the hash table is shown. List
elements as allocated by malloc are shown in the figure. The symbol to the left of each list
element (A, B, C,...) is the address returned by malloc. Entries that are freed are maintained in a
last-in-first-out (LIFO) free list.
Execute the access trace shown in the table below. For ease of representation, you may use the
allocated blocks in any order. Show pointers both by their (symbolic) value, and with an arrow.
If a value changes, cross it out and place the new value to the right. If a pointer changes, also
place an x on the corresponding arrow, and draw the new arrow.
Buckets (Hash Anchor Table)
3
A
A
2
19
D
G
E
H
F
I
555
B
0
1
B
0
38
333
0
C
Hash Table Access Trace
#
1
2
3
4
op
insert
insert
insert
insert
key
27
32
19
43
value
111
222
444
777
#
5
6
7
8
2
op
remove
remove
insert
insert
key
38
27
22
16
value
n/a
n/a
888
999
ECE 2035
4 problems, 5 pages
Programming HW/SW Systems
Fall 2014
Exam Three
Problem 2 (3 parts, 25 points)
19 November 2014
Associative Set Performance
Consider a hash table that is implemented using the following struct definitions.
#define NUMBUCKETS
13
typedef struct Entry {
int
Key;
int
Value;
struct Entry *Next;
} Entry;
typedef struct {
Entry
*Buckets[NUMBUCKETS];
int
Size;
} HashTable;
Suppose the entries are maintained in a sorted linked list in order of increasing key values in each bucket.
Part A (8 points) Complete the C function Find_Key that efficiently searches the hash table for an entry
corresponding to a specified key. It should return a pointer to the matching Entry if Key is found or
return NULL if Key is not found in the hash table.
Entry *Find_Key(HashTable *HT, int Key) {
Entry
*ThisEntry;
int
Index;
int
Hash(int Key); /* function prototype for hash function */
}
Part B (10 points) Suppose a hash table created using the structs above contains 312 entries total and the
entries are evenly distributed across the hash table buckets. Assume that computing the hash function
takes an average of two operations and comparing two keys takes an average of twelve operations.
Suppose that two thirds of keys looked up are found in the hash table and one third are not found. How
many of these operations would be required for the average lookup in the hash table if the bucket list is
unsorted versus sorted? (Show work.)
Number of operations when each bucket list is unsorted:
Number of operations when each bucket list is sorted:
Part C (7 points) Suppose the hash table automatically resizes (with the same 312 entries and found key
probabilities) so that the average access time becomes 70 operations. How many hash table buckets are
being used, assuming each bucket contains an unsorted list of entries? (Show work.)
New number of buckets:
3
ECE 2035
Programming HW/SW Systems
4 problems, 5 pages
Fall 2014
Exam Three
19 November 2014
Problem 3 (5 parts, 25 points)
Heap Management
Below is a snapshot of heap storage. Values that are pointers are denoted with a “$”. The heap
pointer is $6152. The heap has been allocated contiguously beginning at $6000, with no gaps
between objects.
addr
6000
6004
6008
6012
6016
6020
6024
6028
value
12
24
4
16
12
$6004
$6080
$6048
addr
6032
6036
6040
6044
6048
6052
6056
6060
value
8
6080
10
12
16
6032
$6100
4
addr
6064
6068
6072
6076
6080
6084
6088
6092
value
$6020
4
20
16
128
604
4
6080
addr
6096
6100
6104
6108
6112
6116
6120
6124
value
8
$6048
16
12
152
8
16
24
addr
6128
6132
6136
6140
6144
6148
6152
6156
value
0
4
6032
0
24
0
0
0
addr
6160
6164
6168
6172
6176
6180
6184
6188
value
0
0
0
0
0
0
0
0
Part A (8 points) Suppose the stack holds a local variable whose value is the memory address
$6064 and register $5 holds the address $6080. No other registers or static variables currently
hold heap memory addresses. List the addresses of all objects in the heap that are not garbage.
Addresses of Non-Garbage Objects:
Part B (5 points) Create a free list by scanning the heap memory for garbage, starting at address
6000 and placing objects on the free list so that a first-fit allocation strategy will also always
produce the best-fit.
Free List:
Part C (3 points) Based on the free list created in part B, if an object of size 27 bytes is
allocated, what address will be returned using a first-fit allocation strategy? How many bytes of
slack (if any) will result?
Address:
Slack:
Part D (3 points) Based on the free list created in part B, if an object of size 16 bytes is
allocated, what address will be returned using a best-fit allocation strategy? How many bytes of
slack (if any) will result?
Address:
Slack:
Part E (6 points) If the local variable whose value is the address $6064 is popped from the stack,
which addresses will be reclaimed by each of the following strategies? If none, write “none.”
(You need not list addresses already on the free list from part B.)
Reference Counting:
Mark and Sweep:
Old-New Space (copying):
4
ECE 2035
4 problems, 5 pages
Programming HW/SW Systems
Fall 2014
Exam Three
Problem 4 (6 parts, 25 points)
19 November 2014
Dynamic Allocation on Heap
Suppose you are developing a path planning application for an autonomous aerial vehicle. Complete the
following C code by following the steps below:
typedef struct WayPoint {
double Altitude;
float
Longitude;
float
Latitude;
struct WayPoint *Next;
} WayPoint;
WayPoint *Path = NULL;
void Add_WayPoint(float La, float Lo, double A){
; /* part A*/
; /* part B*/
if (
){
/* part D */
printf(“Error: Insufficient space.”);
exit(1);
}
; /* part E*/
; /* part E*/
; /* part E*/
; /* part F*/
; /* part F*/
}
Part A (3 points) Add a local variable called NewPoint that is a pointer to a WayPoint object.
Part B (6 points) Allocate space for a WayPoint structure using malloc and make NewPoint point to
the object allocated. Be sure to include appropriate type casting to avoid type errors.
Part C (3 points) How many bytes are allocated in Part B for the WayPoint structure, excluding its size
header? Assume a 32-bit system.
bytes
Part D (4 points) Fill in the test for whether malloc found enough space which controls the print
statement.
Part E (3 points) Initialize the fields (Altitude, Longitude, Latitude) of the newly allocated
WayPoint object to the values of the 3 input parameters (A, Lo, La, respectively).
Part F (6 points) Push the newly allocated WayPoint object onto the front of the list of WayPoint
objects pointed to by the global variable Path.
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