I have to write a Perl script that converts a binary number, specified as an
argument, to a decimal number. In the question there's a hint to use the reverse function.
We have to assume that the binary number is in this format
EDIT: This is what I've progressed to (note this is code from my textbook that I've messed with):
#!/usr/bin/perl
# dec2.pl: Converts decimal number to binary
#
die("No arguments\n") if ( $#ARGV == -1 ) ;
foreach $number (#ARGV) {
$original_number = $number ;
until ($number == 0 ) {
$bit = $number % 2 ;
unshift (#bit_arr, $bit) ;
$number = int($number / 2 );
}
$binary_number = join ("", #bit_arr) ;
print reverse ("The decimal number of $binary_number is $original_number\n");
$#bit_arr = -1;
}
When executed:
>./binary.pl 8
The decimal number of 1000 is 8
I don't know how to word it to make the program know to add up all of the 1's in the number that is inputted.
You could just use sprintf to do the converting for you...
sprintf("%d", 0b010101); # Binary string 010101 -> Decimal 21
sprintf("%b", 21) # Decimal 21 -> Binary 010101 string
Of course, you can also just eval a binary string with 0b in front to indicate binary:
my $binary_string = '010101';
my $decimal = eval("0b$binary"); # 21
You don't have to use reverse, but it makes it easy to think about the problem with respect to exponents and array indices.
use strict;
use warnings;
my $str = '111110100';
my #bits = reverse(split(//, $str));
my $sum = 0;
for my $i (0 .. $#bits) {
next unless $bits[$i];
$sum += 2 ** $i;
}
First of all, you are suppose to convert from a binary to decimal, not the other way around, which you means you take an input like $binary = '1011001';.
The first thing you need to do is obtain the individual bits (a0, a1, etc) from that. We're talking about splitting the string into its individual digits.
for my $bit (split(//, $binary)) {
...
}
That should be a great starting point. With that, you have all that you need to apply the following refactoring of the formula you posted:
n = ( ( ( ... )*2 + a2 )*2 + a1 )*2 + a0
[I have no idea why reverse would be recommended. It's possible to use it, but it's suboptimal.]
Related
Read a file that contains an address and a data, like below:
#0, 12345678
#1, 5a5a5a5a
...
My aim is to read the address and the data. Consider the data I read is in hex format, and then I need to unpack them to binary number.
So 12345678 would become 00010010001101000101011001111000
Then, I need to further unpack the transferred binary number to another level.
So it becomes, 00000000000000010000000000010000000000000001000100000001000000000000000100000001000000010001000000000001000100010001000000000000
They way I did is like below
while(<STDIN>) {
if (/\#(\S+)\s+(\S+)/) {
$addr = $1;
$data = $2;
$mem{$addr} = ${data};
}
}
foreach $key (sort {$a <=> $b} (keys %mem)) {
my $str = unpack ('B*', pack ('H*',$mem{$key}));
my $str2 = unpack ('B*', pack ('H*', $str));
printf ("#%x ", $key);
printf ("%s",$str2);
printf ("\n");
}
It works, however, my next step is to do some numeric operation on the transferred bits.
Such as bitwise or and shifting. I tried << and | operator, both are for numbers, not strings. So I don't know how to solve this.
Please leave your comments if you have better ideas. Thanks.
You can employ Bit::Vector module from metaCPAN
use strict;
use warnings;
use Bit::Vector;
my $str = "1111000011011001010101000111001100010000001111001010101000111010001011";
printf "orig str: %72s\n", $str;
#only 72 bits for better view
my $vec = Bit::Vector->new_Bin(72,$str);
printf "vec : %72s\n", $vec->to_Bin();
$vec->Move_Left(2);
printf "left 2 : %72s\n", $vec->to_Bin();
$vec->Move_Right(4);
printf "right 4 : %72s\n", $vec->to_Bin();
prints:
orig str: 1111000011011001010101000111001100010000001111001010101000111010001011
vec : 001111000011011001010101000111001100010000001111001010101000111010001011
left 2 : 111100001101100101010100011100110001000000111100101010100011101000101100
right 4 : 000011110000110110010101010001110011000100000011110010101010001110100010
If you need do some math with arbitrary precision, you can also use Math::BigInt or use bigint (http://perldoc.perl.org/bigint.html)
Hex and binary are text representation of numbers. Shifting and bit manipulations are numerical operations. You want a number, not text.
my $hex = '5a5a5a5a';
$num = hex($hex); # Convert to number.
$num >>= 1; # Manipulate the number.
$hex = sprintf('%08X', $num); # Convert back to hex.
In a comment, you mention you want to deal with 256 bit numbers. The native numbers don't support that, but you can use Math::BigInt.
My final solution of this is forget about treat them as numbers, just treat them as string . I use substring and string concentration instead of shift. Then for the or operation , I just add each bit of the string, if it's 0 the result is 0, else is 1.
It may not be the best way to solve this problem. But that's the way I finally used.
I have a tab delimited file with several columns (9 columns) that looks like this:
1:21468 1 21468 2.8628817609765984 0.09640845515631684 0.05034710996552612 1.0 0.012377712911711025 54.0
However in column 5 I sometimes have scientific numbers like:
8.159959468796783E-4
8.465114165595303E-4
8.703354859736187E-5
9.05132870067004E-4
I need to have all numbers in column 5 in decimal notation. From the example above:
0.0008159959468796783
0.0008465114165595303
0.00008703354859736187
0.000905132870067004
And I need to change these numbers without changing the rest of the numbers in column 5 or the rest of the file.
I know there is a similar post in Convert scientific notation to decimal in multiple fields. But in this case there was a if statement not related to the type of number present in the field, and it was for all numbers in that column. So, I'm having trouble transforming the information in there to my specific case. Can someone help me figuring this out?
Thank you!
The easyiest (and fastest) way to convert a scientific notation number in perl, to a regular notation number:
my $num = '0.12345678E5';
$num *= 1;
print "$num\n";
As Jim already proposed, one way to do this is to simply treat the number as a string and do the translation yourself. This way you're able to fully maintain your significant digits.
The following demonstrates a function for doing just that. It takes in a number that's potentially in scientific notation, and it returns the decimal representation. Works with both positive and negative exponents:
use warnings;
use strict;
while (<DATA>) {
my ($num, $expected) = split;
my $dec = sn_to_dec($num);
print $dec . ' - ' . ($dec eq $expected ? 'good' : 'bad') . "\n";
}
sub sn_to_dec {
my $num = shift;
if ($num =~ /^([+-]?)(\d*)(\.?)(\d*)[Ee]([-+]?\d+)$/) {
my ($sign, $int, $period, $dec, $exp) = ($1, $2, $3, $4, $5);
if ($exp < 0) {
my $len = 1 - $exp;
$int = ('0' x ($len - length $int)) . $int if $len > length $int;
substr $int, $exp, 0, '.';
return $sign.$int.$dec;
} elsif ($exp > 0) {
$dec .= '0' x ($exp - length $dec) if $exp > length $dec;
substr $dec, $exp, 0, '.' if $exp < length $dec;
return $sign.$int.$dec;
} else {
return $sign.$int.$period.$dec;
}
}
return $num;
}
__DATA__
8.159959468796783E-4 0.0008159959468796783
8.465114165595303E-4 0.0008465114165595303
8.703354859736187E-5 0.00008703354859736187
9.05132870067004E-4 0.000905132870067004
9.05132870067004E+4 90513.2870067004
9.05132870067004E+16 90513287006700400
9.05132870067004E+0 9.05132870067004
If you do this the simple way, by parsing as floating point and then using printf to force it to print as a decimal, you may end up with slightly different results because you're at the upper limit of precision available in double-precision format.
What you should do is split each line into fields, then examine field 5 with something like this.
($u,$d,$exp) = $field[5] =~ /(\d)\.(\d+)[Ee]([-+]\d+)/
If field[5] is in scientific notation this will give you
$u the digit before the decimal
$d the digits after the decimal
$exp the exponent
(if it's not you'll get back undefined values and can just skip the reformatting step)
Using that information you can reassemble the digits with the correct number of leading zeros and decimal point. If the exponent is positive you have to reassemble the digits but then insert the decimal point in the right place.
Once you've reformatted the value the way you want, reassemble the entire line (using, say, join) and write it out.
could soemone help me with the following condition, please?
I'm trying to compare $price and $lsec.
if( (sprintf("%.2f", ($price*100+0.5)/100)*1 != $lsec*1) )
{
print Dumper($price,$lsec)
}
Sometimes the dumper prints same numbers(as strings) and jumps in.
Thought, that multiplying with 1 makes floats from them...
Here dumper output:
$VAR1 = '8.5';
$VAR2 = '8.5';
What am I doing wrong?
Thank you,
Greetings and happy easter.
There is a difference between what is stored in a Perl variable and how it is used. You are correct that multiplying by 1 forces a variable to be used as a number. It also causes the number to be stored in the SV data structure that represents the variable to the interpreter. You can use the Devel::Peek module to see what Perl has stored in each variable:
use Devel::Peek;
my $num = "8.5";
Dump $num;
outputs:
SV = PV(0xa0a46d8) at 0xa0c3f08
REFCNT = 1
FLAGS = (POK,pPOK)
PV = 0xa0be8c8 "8.5"\0
CUR = 3
LEN = 4
continuing...
my $newnum = $num * 1;
Dump $num;
Dump $newnum;
outputs:
SV = PVNV(0xa0a46d8) at 0xa0c3f08
REFCNT = 1
FLAGS = (PADMY,NOK,POK,pIOK,pNOK,pPOK)
IV = 8
NV = 8.5
PV = 0xa0be8c8 "8.5"\0
CUR = 3
LEN = 4
SV = NV(0x9523660) at 0x950df20
REFCNT = 1
FLAGS = (PADMY,NOK,pNOK)
NV = 8.5
The attributes we are concerned with are PV (string pointer), NV (floating-point number), and IV (integer). Initially, $num only has the string value, but using it as a number (e.g. in multiplication) causes it to store the numeric values. However, $num still "remembers" that it is a string, which is why Data::Dumper treats it like one.
For most purposes, there is no need to explicitly force the use of a string as a number, since operators and functions can use them in the most appropriate form. The == and != operators, for example, coerce their operands into numeric form to do numeric comparison. Using eq or ne instead forces a string comparison. This is one more reason to always use warnings in your Perl scripts, since trying to compare a non-numeric string with == will garner this warning:
Argument "asdf" isn't numeric in numeric eq (==) at -e line 1.
You are correct to say that multiplying a string by 1 will force it to be evaluated as a number, but the numeric != comparator will do the same thing. This is presumably a technique you have acquired from other languages as Perl will generally do the right thing and there is no need to force a cast of either operand.
Lets take a look at the values you're comparing:
use strict;
use warnings;
use Data::Dumper;
my $price = '8.5';
my $lsec = '8.5';
my $rounded_price = sprintf("%.2f", ($price * 100 + 0.5) / 100);
print "$rounded_price <=> $lsec\n";
if ( $rounded_price != $lsec ) {
print Dumper($price,$lsec);
}
output
8.51 <=> 8.5
$VAR1 = '8.5';
$VAR2 = '8.5';
So Perl is correctly saying that 8.51 is unequal to 8.5.
I suspect that your
($price * 100 + 0.5) / 100
is intended to round $price to two decimal places, but all it does in fact is to increase $price by 0.005. I think you meant to write
int($price * 100 + 0.5) / 100
but you also put the value through sprintf which is another way to do the same thing.
Either
$price = int($price * 100 + 0.5) / 100
or
$price = sprintf ".2f", $price
but both is overkill!
This part:
($price*100+0.5)/100)
If you put in 8.5, you get back 8.505. Which naturally is not equal to 8.5. Since you do not change $price, you do not notice any difference.
Perl handles conversion automatically, so you do not need to worry about that.
my $x = "8.5";
my $y = 8.5;
print "Equal" if $x == $y; # Succeeds
The nature of the comparison, == or in your case != converts the arguments to numeric, whether they are numeric or not.
You're doing nothing wrong. Perl converts it to a string before dumping it. For comparisons, use == and != for numeric comparisons and eq and ne for a string comparisons. Perl converts to strings and numbers as needed.
Example:
$ perl -MData::Dumper -e "my $a=3.1415; print Dumper($a);"
$VAR1 = '3.1415';
I'm trying to parse CPU node affinity+cache sibling info in Linyx sysfs.
I can get a string of bits, just for example:
0000111100001111
Now I need a function where I have a decimal number (e.g. 4 or 5) and I need to test whether the nth bit is set or not. So it would return true for 4 and false for 5. I could create a string by shifting 1 n number of times, but I'm not sure about the syntax, and is there an easier way? Also, there's no limit on how long the string could be, so I want to avoid decimal <-> binary conversoins.
Assuming that you have the string of bits "0000111100001111" in $str, if you do the precomputation step:
my $bit_vector = pack "b*", $str;
you can then use vec like so:
$is_set = vec $bit_vector, $offset, 1;
so for example, this code
for (0..15) {
print "$_\n" if vec $bit_vector, $_, 1;
}
will output
4
5
6
7
12
13
14
15
Note that the offsets are zero-based, so if you want the first bit to be bit 1, you'll need to add/subtract 1 yourself.
Well, this seems to work, and I'm not going for efficiency:
sub is_bit_set
{
my $bitstring = shift;
my $bit = shift;
my $index = length($bitstring) - $bit - 1;
if (substr($bitstring, $index, 1) == "1") {
return 1;
}
else {
return 0;
}
}
Simpler variant without bit vector, but for sure vector would be more efficient way to deal.
sub is_bit_set
{
my $bitstring = shift;
my $bit = shift;
return int substr($bitstring, -$bit, 1);
}
How can I round a decimal number (floating point) to the nearest integer?
e.g.
1.2 = 1
1.7 = 2
Output of perldoc -q round
Does Perl have a round() function? What about ceil() and floor()?
Trig functions?
Remember that int() merely truncates toward 0. For rounding to a certain number of digits, sprintf() or printf() is usually the easiest
route.
printf("%.3f", 3.1415926535); # prints 3.142
The POSIX module (part of the standard Perl distribution) implements
ceil(), floor(), and a number of other mathematical and trigonometric
functions.
use POSIX;
$ceil = ceil(3.5); # 4
$floor = floor(3.5); # 3
In 5.000 to 5.003 perls, trigonometry was done in the Math::Complex
module. With 5.004, the Math::Trig module (part of the standard Perl
distribution) implements the trigonometric functions. Internally it
uses the Math::Complex module and some functions can break out from the
real axis into the complex plane, for example the inverse sine of 2.
Rounding in financial applications can have serious implications, and
the rounding method used should be specified precisely. In these
cases, it probably pays not to trust whichever system rounding is being
used by Perl, but to instead implement the rounding function you need
yourself.
To see why, notice how you'll still have an issue on half-way-point
alternation:
for ($i = 0; $i < 1.01; $i += 0.05) { printf "%.1f ",$i}
0.0 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7
0.8 0.8 0.9 0.9 1.0 1.0
Don't blame Perl. It's the same as in C. IEEE says we have to do
this. Perl numbers whose absolute values are integers under 2**31 (on
32 bit machines) will work pretty much like mathematical integers.
Other numbers are not guaranteed.
Whilst not disagreeing with the complex answers about half-way marks and so on, for the more common (and possibly trivial) use-case:
my $rounded = int($float + 0.5);
UPDATE
If it's possible for your $float to be negative, the following variation will produce the correct result:
my $rounded = int($float + $float/abs($float*2 || 1));
With this calculation -1.4 is rounded to -1, and -1.6 to -2, and zero won't explode.
You can either use a module like Math::Round:
use Math::Round;
my $rounded = round( $float );
Or you can do it the crude way:
my $rounded = sprintf "%.0f", $float;
If you decide to use printf or sprintf, note that they use the Round half to even method.
foreach my $i ( 0.5, 1.5, 2.5, 3.5 ) {
printf "$i -> %.0f\n", $i;
}
__END__
0.5 -> 0
1.5 -> 2
2.5 -> 2
3.5 -> 4
See perldoc/perlfaq:
Remember that int() merely truncates toward 0. For rounding to a
certain number of digits, sprintf() or printf() is usually the
easiest route.
printf("%.3f",3.1415926535);
# prints 3.142
The POSIX module (part of the standard Perl distribution)
implements ceil(), floor(), and a number of other mathematical
and trigonometric functions.
use POSIX;
$ceil = ceil(3.5); # 4
$floor = floor(3.5); # 3
In 5.000 to 5.003 perls, trigonometry was done in the Math::Complex module.
With 5.004, the Math::Trig module (part of the standard Perl distribution) > implements the trigonometric functions.
Internally it uses the Math::Complex module and some functions can break
out from the real axis into the complex plane, for example the inverse sine of 2.
Rounding in financial applications can have serious implications, and the rounding
method used should be specified precisely. In these cases, it probably pays not to
trust whichever system rounding is being used by Perl, but to instead implement the
rounding function you need yourself.
To see why, notice how you'll still have an issue on half-way-point alternation:
for ($i = 0; $i < 1.01; $i += 0.05)
{
printf "%.1f ",$i
}
0.0 0.1 0.1 0.2 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.8 0.8 0.9 0.9 1.0 1.0
Don't blame Perl. It's the same as in C. IEEE says we have to do
this. Perl numbers whose absolute values are integers under 2**31 (on
32 bit machines) will work pretty much like mathematical integers.
Other numbers are not guaranteed.
You don't need any external module.
$x[0] = 1.2;
$x[1] = 1.7;
foreach (#x){
print $_.' = '.( ( ($_-int($_))<0.5) ? int($_) : int($_)+1 );
print "\n";
}
I may be missing your point, but I thought this was much cleaner way to do the same job.
What this does is to walk through every positive number in the element, print the number and rounded integer in the format you mentioned. The code concatenates respective rounded positive integer only based on the decimals. int($_) basically round-down the number so ($-int($)) captures the decimals. If the decimals are (by definition) strictly less than 0.5, round-down the number. If not, round-up by adding 1.
The following will round positive or negative numbers to a given decimal position:
sub round ()
{
my ($x, $pow10) = #_;
my $a = 10 ** $pow10;
return (int($x / $a + (($x < 0) ? -0.5 : 0.5)) * $a);
}
Following is a sample of five different ways to summate values. The first is a naive way to perform the summation (and fails). The second attempts to use sprintf(), but it too fails. The third uses sprintf() successfully while the final two (4th & 5th) use floor($value + 0.5).
use strict;
use warnings;
use POSIX;
my #values = (26.67,62.51,62.51,62.51,68.82,79.39,79.39);
my $total1 = 0.00;
my $total2 = 0;
my $total3 = 0;
my $total4 = 0.00;
my $total5 = 0;
my $value1;
my $value2;
my $value3;
my $value4;
my $value5;
foreach $value1 (#values)
{
$value2 = $value1;
$value3 = $value1;
$value4 = $value1;
$value5 = $value1;
$total1 += $value1;
$total2 += sprintf('%d', $value2 * 100);
$value3 = sprintf('%1.2f', $value3);
$value3 =~ s/\.//;
$total3 += $value3;
$total4 += $value4;
$total5 += floor(($value5 * 100.0) + 0.5);
}
$total1 *= 100;
$total4 = floor(($total4 * 100.0) + 0.5);
print '$total1: '.sprintf('%011d', $total1)."\n";
print '$total2: '.sprintf('%011d', $total2)."\n";
print '$total3: '.sprintf('%011d', $total3)."\n";
print '$total4: '.sprintf('%011d', $total4)."\n";
print '$total5: '.sprintf('%011d', $total5)."\n";
exit(0);
#$total1: 00000044179
#$total2: 00000044179
#$total3: 00000044180
#$total4: 00000044180
#$total5: 00000044180
Note that floor($value + 0.5) can be replaced with int($value + 0.5) to remove the dependency on POSIX.
Negative numbers can add some quirks that people need to be aware of.
printf-style approaches give us correct numbers, but they can result in some odd displays. We have discovered that this method (in my opinion, stupidly) puts in a - sign whether or not it should or shouldn't. For example, -0.01 rounded to one decimal place returns a -0.0, rather than just 0. If you are going to do the printf style approach, and you know you want no decimal, use %d and not %f (when you need decimals, it's when the display gets wonky).
While it's correct and for math no big deal, for display it just looks weird showing something like "-0.0".
For the int method, negative numbers can change what you want as a result (though there are some arguments that can be made they are correct).
The int + 0.5 causes real issues with -negative numbers, unless you want it to work that way, but I imagine most people don't. -0.9 should probably round to -1, not 0. If you know that you want negative to be a ceiling rather than a floor then you can do it in one-liner, otherwise, you might want to use the int method with a minor modification (this obviously only works to get back whole numbers:
my $var = -9.1;
my $tmpRounded = int( abs($var) + 0.5));
my $finalRounded = $var >= 0 ? 0 + $tmpRounded : 0 - $tmpRounded;
If you are only concerned with getting an integer value out of a whole floating point number (i.e. 12347.9999 or 54321.0001), this approach (borrowed and modified from above) will do the trick:
my $rounded = floor($float + 0.1);
My solution for sprintf
if ($value =~ m/\d\..*5$/){
$format =~ /.*(\d)f$/;
if (defined $1){
my $coef = "0." . "0" x $1 . "05";
$value = $value + $coef;
}
}
$value = sprintf( "$format", $value );
loads of reading documentation on how to round numbers, many experts suggest writing your own rounding routines, as the 'canned' version provided with your language may not be precise enough, or contain errors. i imagine, however, they're talking many decimal places not just one, two, or three. with that in mind, here is my solution (although not EXACTLY as requested as my needs are to display dollars - the process is not much different, though).
sub asDollars($) {
my ($cost) = #_;
my $rv = 0;
my $negative = 0;
if ($cost =~ /^-/) {
$negative = 1;
$cost =~ s/^-//;
}
my #cost = split(/\./, $cost);
# let's get the first 3 digits of $cost[1]
my ($digit1, $digit2, $digit3) = split("", $cost[1]);
# now, is $digit3 >= 5?
# if yes, plus one to $digit2.
# is $digit2 > 9 now?
# if yes, $digit2 = 0, $digit1++
# is $digit1 > 9 now??
# if yes, $digit1 = 0, $cost[0]++
if ($digit3 >= 5) {
$digit3 = 0;
$digit2++;
if ($digit2 > 9) {
$digit2 = 0;
$digit1++;
if ($digit1 > 9) {
$digit1 = 0;
$cost[0]++;
}
}
}
$cost[1] = $digit1 . $digit2;
if ($digit1 ne "0" and $cost[1] < 10) { $cost[1] .= "0"; }
# and pretty up the left of decimal
if ($cost[0] > 999) { $cost[0] = commafied($cost[0]); }
$rv = join(".", #cost);
if ($negative) { $rv = "-" . $rv; }
return $rv;
}
sub commafied($) {
#*
# to insert commas before every 3rd number (from the right)
# positive or negative numbers
#*
my ($num) = #_; # the number to insert commas into!
my $negative = 0;
if ($num =~ /^-/) {
$negative = 1;
$num =~ s/^-//;
}
$num =~ s/^(0)*//; # strip LEADING zeros from given number!
$num =~ s/0/-/g; # convert zeros to dashes because ... computers!
if ($num) {
my #digits = reverse split("", $num);
$num = "";
for (my $i = 0; $i < #digits; $i += 3) {
$num .= $digits[$i];
if ($digits[$i+1]) { $num .= $digits[$i+1]; }
if ($digits[$i+2]) { $num .= $digits[$i+2]; }
if ($i < (#digits - 3)) { $num .= ","; }
if ($i >= #digits) { last; }
}
#$num =~ s/,$//;
$num = join("", reverse split("", $num));
$num =~ s/-/0/g;
}
if ($negative) { $num = "-" . $num; }
return $num; # a number with commas added
#usage: my $prettyNum = commafied(1234567890);
}
Using Math::BigFloat you can do something like this:
use Math::BigFloat;
print Math::BigFloat->new(1.2)->bfround(1); ## 1
print Math::BigFloat->new(1.7)->bfround(1); ## 2
This can be wrapped in a subroutine
use Math::BigFloat;
sub round {
Math::BigFloat->new(shift)->bfround(1);
}
print round(1.2); ## 1
print round(1.7); ## 2
cat table |
perl -ne '/\d+\s+(\d+)\s+(\S+)/ && print "".**int**(log($1)/log(2))."\t$2\n";'