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# calulating parity

Posted on 2001-06-27
Medium Priority
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hi ,

input = file with numerical lines :
example :

1000c5c548a0000650e21b42d04554374
0000809d1dc0141450ee139814b014398
1000aaaa41e8ce2050ed4a587eb554394
00003d8b4f01f1e9511d1358000094450
0000c94b1e402e7050da0f180b1c9435c

assumptions :
1. digits can be either decimal or hex'
2. lines may include spaces between fields
3. lines may be different long (in example all lines are 33 char's long)
4. no blank lines

required script :
get input_file + base (default base = hex)
output :
numbers of lines whose parity is odd
+ print line

* if you know perl , it can be also in perl .

Talmash

*** don't think its homework ... I am a hardware engineer , I need this script to debug a bus of data from an external SRAM to the CHIP we design .

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Question by:Talmash
• 5
• 3

LVL 5

Expert Comment

ID: 6231796
Try this

#!/usr/bin/perl

use Math::BigInt;

(\$filename, \$base) = @ARGV;

open IN, \$filename or die \$!;
@lines = <IN>;
close IN;
\$oddlines = 0;

chomp @lines;
foreach \$line (@lines) {
if (\$base == 10) { # base 10
\$i = new Math::BigInt \$line;
\$bits = 0;
while (\$i != 0) {
\$bits += \$i % 2;
\$i /= 2;
}
} else { # base 16
\$bits = 0;
foreach \$byte (split // , \$line) {
\$line =~ /\s/ && next;
\$bits += \$_ foreach (split //, unpack("b4",pack("h", \$byte)));
}
}
\$parity = \$bits % 2;
if (\$parity) {
\$oddlines++;
print "\$line\n";
}
}

print "number of odd parity lines = \$oddlines\n";

0

LVL 5

Expert Comment

ID: 6231820
two errors.
chomp @lines;
after close IN;

\$byte =~ /\s/ && next;
0

LVL 6

Author Comment

ID: 6231934
hi marecs

tnx for the work .
I run your suggestion , with the corrections .

result :
18:21{184}bin> par_check tmp

I changed 1st line to :
#!/usr/local/bin/perl5 -wx

and got this result :
18:21{183}bin> par_check tmp
syntax error at par_check line 35, near "\$_ foreach "
Execution of par_check aborted due to compilation errors.

have you checked the script at your machine , and it worked?

any way , I rise points for your efforts .

be sure grade will be A .

Talmash
0

LVL 5

Expert Comment

ID: 6231973
Talmash,

Yes, it definitely worked on my machine.It may not be bug free, because I only tried a few simple lines that I know the parity of.

Try this instead of line 35

foreach (split //, unpack("b4",pack("h", \$byte))) {
\$bits += \$_;
}

0

LVL 6

Author Comment

ID: 6234067
EXCELLENT !

great job .

I may be too excited , but it works just fine .

I used lines with spaces ,

short and long lines together .

BUT , base 10 doesn't work properely .

try this example :

100
064372 56783537634 0349361354384
00009  659256336 4776330328000094418
100003392440203476430343772614343
000033333931419976495558148314480
100093834420000676440998054414444

command line : par_check in_file 10

Talmash
0

LVL 5

Expert Comment

ID: 6234364
Talmash,

I am not clear about a few things.

With
100003392440203476430343772614343
do you mean the 107 bit number
10011101110001110000110001101101010100000110111010000111000011001111000001000111000000101001010111011000111
And you want to know the parity of this number? This particular number has even parity?

064372 56783537634 0349361354384 actually has 3 numbers in the line, and the parity of each number must be calculated seperately? Do you then want the number of fields who's parity is odd, rather than the number of lines?
0

LVL 5

Accepted Solution

marecs earned 800 total points
ID: 6235380
This assumes that the answers to my previous post are true.

#!/usr/bin/perl -w

use Math::BigInt;

(\$filename, \$base) = @ARGV;
defined(\$base) or \$base = 16;

open IN, \$filename or die \$!;
@lines = ();
\$/ = undef;
push @lines , split /\s+/, <IN>;
close IN;

\$oddlines = 0;

foreach \$line (@lines) {
if (\$base == 10) { # base 10
\$i = new Math::BigInt \$line;
\$bits = 0;
while (\$i != 0) {
\$bits += \$i % 2;
\$i /= 2;
}
} else { # base 16
\$bits = 0;
foreach \$byte (split // , \$line) {
foreach (split //, unpack("b4",pack("h", \$byte))) {
\$bits += \$_;
}
}
}
\$parity = \$bits % 2;
if (\$parity) {
\$oddlines++;
print "\$line\n";
}
}

print "number of odd parity fields = \$oddlines\n";
0

LVL 85

Expert Comment

ID: 6235959
#an easier way to calculate parity for base 16 is
\$parity ^= unpack"%1b*",pack"h*", \$line;

0

LVL 6

Author Comment

ID: 6241920
hi ,

as I said before , you deserve it , for your quick response.
about decimal lines : It is low priority by now , so lets
forget our little bug.

as to ozo , I'll check your proposed line .

tnx all ,

question is closed .

Tal
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