Software 1 - Bitwise operations, make, and perl(12)

administrivia

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

Assignment 5

• The dependency graph

make example

• GNU make
• makefile for bfs assignment

  CSOURCES = bfs.c memory_man.c OBJECTS = $(CSOURCES:.c=.o) TARGET = $(firstword $(CSOURCES:.c=)) CFLAGS = -Wall -pedantic $(TARGET): $(OBJECTS) clean: rm -rf $(OBJECTS) $(TARGET)

The implicit rules (for the example)

• Compiling the sources:

  %.o : %.c $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

• Linking the objects:

  bfs: bfs.o memory_man.o $(CC) $(LDFLAGS) $? $(LOADLIBES) $(LDLIBS) -o $@

make

• If .DELETE_ON_ERROR is mentioned as a target anywhere in the makefile, then make will delete the target of a rule if it has changed and its commands exit with a nonzero exit status.

  .DELETE_ON_ERROR: *.e

Perl

• Programming Perl
• Perl for windows - ActivePerl

Perl - die

• die LIST

• Prints the concatenated value of LIST to STDERR and exits with the current value of $! (errno).
  • If $! is 0, then there is more to it...

Perl - open

• open FILEHANDLE, EXPR
  open FILEHANDLE

• Opens the file whose filename is given by EXPR, and associates it with FILEHANDLE
• If EXPR is omitted, the scalar variable of the same name as the FILEHANDLE must contain the filename
• Opening a file for writing

  open(INST_H, ">inst.h") or die "Failed to open inst.h: $!\n";

• The relatedness of a filehandle and a variable of the same name

  $ARTICLE = "/usr/spool/news/comp/lang/perl/misc/38245"; open ARTICLE or die "Can't find article $ARTICLE: $!\n"; while (<ARTICLE>) {...

Perl - null filehandle

• Using the null filehandle within the angle operator <> is special
• When you read lines from <>, it magically gives you all the lines from all the files mentioned on the command line. If no files were mentioned, it gives you standard input instead,
  • Emulates the command-line behavior of typical UNIX filter programs such as sed and awk.
• The first time <> is evaluated, the @ARGV array is checked, and if it is null, $ARGV[0] is set to "-", which when opened gives you standard input.
• The @ARGV array is then processed as a list of filenames.

  while (<>) { ... # code for each line }

Perl - split

• split /PATTERN/, EXPR

• Scans a string given by EXPR for delimiters, and splits the string into a list of substrings, returning the resulting list value in list context,
  • or the count of substrings in scalar context

  ($token1, $token3, $token4) = split(" ", $line);

Perl - print

• print FILEHANDLE LIST
  print LIST
  print
  printf FILEHANDLE FORMAT LIST
  printf FORMAT LIST
  

• print prints a string or a comma-separated list of strings to FILEHANDLE or, if omitted, the currently selected output filehandle, initially STDOUT.
• printf prints a formatted string

• printf SOMEHANDLE "some tokens: %s %s %s\n", $token1, $token2, $token3;

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