Positive Values Have 0 in Left-Most Bit
CSE230
Bitwise Operators
Enumeration Type
Struct & Union
2’s Complement Notation
•Positive values have 0 in left-most bit.
•To negate a positive value, complement (“flip”) each bit and then add 1 to the result.
(Negative values have 1 in the left-most bit.)
•Example:
010101012 = +8510
Complement each bit:101010102
Add 1:101010112 = -8510
Bitwise Operators
•~ bitwise complement (1’s complement)
•bitwise AND
•| bitwise OR
•^ bitwise XOR (exclusive OR)
•left shift
•right shift
Logical Operators
short int a = 0x1234,
b = 0x5678,
c = 0x9abc;
printf(“%x\n%x\n%x\n%x\n%x\n”,
~a,a & b, a | b, a ^ b,a & b | c);
Shift Operators
short int a = 0x1234,
b = 0x5678;
unsigned shortc = 0x9abc;
d = 0xdef0;
printf(“%x\n%x\n%x\n%x\n”,
a < 4,b < 6,c > 3,d > 3);
Masking
•The bitwise-AND operator is often used to mask out specific bits of an integer value.
•Example:
int is_odd(int num)
{
int mask = ______;
return (______);
}
Example (page 338)
#include <limits.h>
void bit_print(int a) {
int i;
int n = sizeof(int) * CHAR_BIT;
int mask = 1 < (______);
for (i = 1; i <= n; ++i) {
putchar(((______) ? ‘0’:‘1’);
a <= 1;
}
} Data Compression
•Bitwise operators can be used to pack data and unpack data.
•PACK - store small data units in large unit
•UNPACK - extract small data units from
large unit
Packing (page 341)
#include <limits.h>
int pack(char a, char b, char c, char d) {
int p = a;
p = (p < CHAR_BIT) | ______;
p = (p < CHAR_BIT) | ______;
p = (p < CHAR_BIT) | ______;
return p;
}
Unpacking
#include <limits.h>
char *unpack(int p) {
char c[4];
c[0] = (p & 0x______) > _____ ;
c[1] = (p & 0x00ff0000) > 16 ;
c[2] = (p & 0x0000ff00) > _____ ;
c[3] = (p & 0x000000ff) ;
return c;
}
Data Record Storage
•Zip Code - 5 digits => _____ bits
•Resident gender - M/F => _____ bit
•First letter of last name=> _____ bits
•Birthday month => _____ bits
•Birthday day=> _____bits
______
32 bits (int)
Example
int make_record(int zipcode,
char gender, char lastname,
int birthmonth, int birthday) {
int record = 0;
record |= zipcode;
record |= ((gender =‘M’) ? ______) < _____;
record |= (lastname - ‘A’ + 1) < _____;
record |= birthmonth < ______;
record |= birthday < ______;
return record;
}
Bit Fields
struct person{
unsigned zip_code:______;
unsigned gender:______;
unsigned first_letter:______;
unsigned birthmonth:_____;
unsigned birthday:______;
};
Access: struct person r;
r.zip_code = 11794;
r.gender = 0;
r.birthday = 30;
Bit Fields (cont’d)
typedef struct { unsigned
zip_code:______,
gender:______,
first_letter:______,
birthmonth:______,
birthday:______;
} person_type;
Access: person_type r;
r.zip_code = 11794; r.gender = 0;
r.birthday = 30;
Arrays of Structs
struct { unsigned
b0:1, b1:1, b2:1, b3:1, b4:1,
b5:1, b6:1, b7:1, b8:1, b9:1,
b10:1, b11:1, b12:1, b13:1, b14:1,
b15:1, b16:1, b17:1, b18:1, b19:1,
b20:1, b21:1, b22:1, b23:1, b24:1,
b25:1, b26:1, b27:1, b28:1, b29:1,
b30:1, b31:1;
} word[1000];
Access: word[34].b5
Enumeration Types
•An enumerated data type is an ordinal data type that lists the valid data values for a variable of this data type.
•The values of the enumerated data type are constants of type int.
•The integer value of the first element of the enumerated data type is 0 by default.
•The values of the enumerated data type elements can be reassigned.
Syntax
enum day {sun, mon, tues, wed, thur, fri, sat};
enum day {sun=____, mon, tues, wed, thur, fri, sat};
enum day {sun=____, mon, tues, wed, thurs=_____, fri, sat};
/* Defining variables */
enum day today, tomorrow, yesterday;
More Syntax
enum weather {sunny, cloudy, rain, snow, thunder, windy} forecast1;
enum {sunny, cloudy, rain, snow, thunder, windy} forecast2;
forecast1 = snow;
if (______)
printf(“Hold on to your hat.\n”);
Example
enum day {sun, mon, tue, wed, thu, fri, sat};
typedef enum day day;
day next_day(day d) {
if (______) return sun;
else return (day)(______);
}
Example: POKER
•Five cards
•Each card has a suit and a value
•Suits: clubs, diamonds, hearts, spades
•Values: ace, 2, 3, ..., 10,
jack (11), queen (12), king (13)
•Ace can be treated as “high” (14) or
“low” (1)
POKER hands
•Straight Flush78910J
•Four of a Kind33 33Q
•Full House6 6 6KK
•FlushA2 4 8J
•Straight45678
•Three of a KindA7QQQ
•Two Pair5599J
•PairA241010
•High Card247JK
Storage of Poker Cards
enum suit {hearts, diamonds, clubs, spades};
enum value {ace=1, two, three, four,
five, six, seven, eight, nine, ten, jack, queen, king};
typedef enum suit suit
typedef enum value value
suit cardsuit[5];
value cardval[5];
Storage of Poker
•Each card can be stored as a struct with two fields: value and suit.
•An array of cards is simply an array of these structs:
struct card {
suit pip;
value rank;
} cards[5];
. . . .
cards[1].rank = ace;
cards[1].pip = clubs;
CardsStraight Flush
int is_straight_flush(suit cardsuit[], int cardval[])
{
if (______(cardsuit, cardval) & ______(cardsuit,
cardval))
return 1;
else return 0;
}
Unions
•A struct that allows one field to have different names and storage types.
•Union can only store one value at a time.
•Example:
union road {
int route_num;
char name[20];
} highway;
highway.route_num = ______;
highway.name = ______;
Unions (cont’d)
•Another example:
union road {
int route_num;
char name[20];
} highways[100];
highways[10].name=______;
highways[10].route_num = ______;
printf(“%c”,highways[10].name[0]);
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