Software 1 - Bitwise operations, fork, & pipes(13)

administrivia

Web Page - http://www.cs.tau.ac.il/~efif/courses/Software1_Spring_04

The Dining Philosophers - the setup

Five philosophers are seated around a round table Each philosopher has a bowl of rice in front Between each philosopher and his neighbor is a chopstick Each philosopher thinks for a while, then gets hungry and wants to eat Eating rice requires 2 chopsticks however there are only five chopsticks at most 2 philosophers can be eating at the same time A philosopher may acquire only the chopsticks to his immediate left or right Once a philosopher possesses two chopsticks, he will eat for a while, then put both chopsticks back down on each side

The Dining Philosophers - the problem

• Find a solution so that
  • deadlock does not occur
  • each philosopher gets to eat fairly often

The Dining Philosophers - the code

• diners.c

Bits and constants

• char, short, int and long are integral types. They store whole-number integers
• Relating bits and constants

  decimal	hex	bit pattern	bit number
  1	0x0001	00000000 00000001	0
  2	0x0002	00000000 00000010	1
  4	0x0004	00000000 00000100	2
  8	0x0008	00000000 00001000	3
  16	0x0010	00000000 00010000	4
  32	0x0020	00000000 00100000	5
  64	0x0040	00000000 01000000	6
  128	0x0080	00000000 10000000	7
  256	0x0100	00000001 00000000	8
  512	0x0200	00000010 00000000	9
  1024	0x0400	00000100 00000000	10
  2048	0x0800	00001000 00000000	11
  4096	0x1000	00010000 00000000	12
  8192	0x2000	00100000 00000000	13
  16384	0x4000	01000000 00000000	14
  32768	0x8000	10000000 00000000	15

• One bit flags #define ACTIVATED 0x0001 #define VIP 0x0002 #define PAST_DUE 0x0004 #define OVER_LIMIT 0x0008 #define STOLEN 0x0010 #define LOST 0x0020 #define PREFERRED_RATE 0x0040

Bitwise operations

• Bitwise "and" operator &
• Bitwise "or" operator |
• Bitwise "exclusive or" operator ^
• Bitwise "ones complement" operator ~
• 

Shifting bits

• Operators >> and << shift the bits of an operand to the right and left resp. a desired number of positions
• Bits shifted out are lost
• For left shifts, bit positions vacated by shifting always filled with zeros
• For right shifts,it positions vacated by shifting filled
  • with zeros for unsigned data type
  • with copy of the highest (sign) bit for signed data type

Bitwise operations

• Staudent account - demonstrate bitwise operations usage for flag handling
  • accounts.c