I have a data structure that I'd like to convert back and forth from hex to binary in Ruby. The simplest approach for a binary to hex is '0010'.to_i(2).to_s(16) - unfortunately this does not preserve leading zeroes (due to the to_i call), as one may need with data structures like cryptographic keys (which also vary with the number of leading zeroes).
Is there an easy built in way to do this?
I think you should have a firm idea of how many bits are in your cryptographic key. That should be stored in some constant or variable in your program, not inside individual strings representing the key:
KEY_BITS = 16
The most natural way to represent a key is as an integer, so if you receive a key in a hex format you can convert it like this (leading zeros in the string do not matter):
key = 'a0a0'.to_i(16)
If you receive a key in a (ASCII) binary format, you can convert it like this (leading zeros in the string do not matter):
key = '101011'.to_i(2)
If you need to output a key in hex with the right number of leading zeros:
key.to_s(16).rjust((KEY_BITS+3)/4, '0')
If you need to output a key in binary with the right number of leading zeros:
key.to_s(2).rjust(KEY_BITS, '0')
If you really do want to figure out how many bits might be in a key based on a (ASCII) binary or hex string, you can do:
key_bits = binary_str.length
key_bits = hex_str.length * 4
The truth is, leading zeros are not part of the integer value. I mean, it's a little detail related to representation of this value, not the value itself. So if you want to preserve properties of representation, it may be best not to get to underlying values at all.
Luckily, hex<->binary conversion has one neat property: each hexadecimal digit exactly corresponds to 4 binary digits. So assuming you only get binary numbers that have number of digits divisible by 4 you can just construct two dictionaries for constructing back and forth:
# Hexadecimal part is easy
hex = [*'0'..'9', *'A'..'F']
# Binary... not much longer, but a bit trickier
bin = (0..15).map { |i| '%04b' % i }
Note the use of String#% operator, that formats the given value interpreting the string as printf-style format string.
Okay, so these are lists of "digits", 16 each. Now for the dictionaries:
hex2bin = hex.zip(bin).to_h
bin2hex = bin.zip(hex).to_h
Converting hex to bin with these is straightforward:
"DEADBEEF".each_char.map { |d| hex2bin[d] }.join
Converting back is not that trivial. I assume we have a "good number" that can be split into groups of 4 binary digits each. I haven't found a cleaner way than using String#scan with a "match every 4 characters" regex:
"10111110".scan(/.{4}/).map { |d| bin2hex[d] }.join
The procedure is mostly similar.
Bonus task: implement the same conversion disregarding my assumption of having only "good binary numbers", i. e. "110101".
"I-should-have-read-the-docs" remark: there is Hash#invert that returns a hash with all key-value pairs inverted.
This is the most straightforward solution I found that preserves leading zeros. To convert from hexadecimal to binary:
['DEADBEEF'].pack('H*').unpack('B*').first # => "11011110101011011011111011101111"
And from binary to hexadecimal:
['11011110101011011011111011101111'].pack('B*').unpack1('H*') # => "deadbeef"
Here you can find more information:
Array#pack: https://ruby-doc.org/core-2.7.1/Array.html#method-i-pack
String#unpack1 (similar to unpack): https://ruby-doc.org/core-2.7.1/String.html#method-i-unpack1
Related
I have a long string which contains only decimal numbers with two signs after comma
str = "123,457568,22321,5484123,77"
The numbers in string only decimals with two signs after comma. How I can separate them in different numbers like that
arr = ["123,45" , "7568,22" , "321,54" , "84123,77"]
You could try a regex split here:
str = "123,457568,22321,5484123,77"
nums = str.split(/(?<=,\d{2})/)
print nums
This prints:
123,45
7568,22
321,54
84123,77
The logic above says to split at every point where a comma followed by two digits precedes.
Scan String for Commas Followed by Two Digits
This is a case where you really need to know your data. If you always have floats with two decimal places, and commas are decimals in your locale, then you can use String#scan as follows:
str.scan /\d+,\d{2}/
#=> ["123,45", "7568,22", "321,54", "84123,77"]
Since your input data isn't consistent (which can be assumed by the lack of a reliable separator between items), you may not be able to guarantee that each item has a fractional component at all, or that the component has exactly two digits. If that's the case, you'll need to find a common pattern that is reliable for your given inputs or make changes to the way you assign data from your data source into str.
I am trying to solve the following problem using Ruby:
I have a requirement to generate strings with variable bits length which contain only alphanumeric characters.
Here is what I have already found:
Digest::SHA2.new(bitlen = 256).to_s
# => "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
It does exactly what I need, but it accepts only 256, 384, and 512 as bitlen.
Does anybody aware of any alternatives?
Thanks in advance.
Update
One byte = collection of 8 bits.
Every alphanumeric character occupies 1 byte according to String#bytesize.
('a'..'z').chain('A'..'Z').chain('0'..'9').map(&:bytesize).uniq
# => [1]
Based on the facts mentioned above, we can suppose that
SecureRandom.alphanumeric(1) generates an alphanumeric string with 8 bits length.
SecureRandom.alphanumeric(2) generates an alphanumeric string with 16 bits length.
SecureRandom.alphanumeric(3) generates an alphanumeric string with 24 bits length.
And so on...
As a result, #anothermh's answer can be considered as an acceptable solution.
Use SecureRandom.
First, make sure you require it:
require 'securerandom'
Then you can generate values:
SecureRandom.alphanumeric(10)
=> "hxYolwzk0P"
Change 10 to whatever length you require.
It's worth pointing out that the example you used was returning not alphanumeric but hexadecimal values. If you specifically require hex then you can use:
SecureRandom.hex(10)
=> "470eb1d8daebacd20920"
I want to create a valid IFC GUID (IfcGloballyUniqueId) according to the specification here:
http://www.buildingsmart-tech.org/ifc/IFC2x3/TC1/html/ifcutilityresource/lexical/ifcgloballyuniqueid.htm
It's basically a UUID or GUID (128 bit) mapped to a set of 22 characters to limit storage space in a text file.
I currently have this workaround, but it's merely an approximation:
guid = '';22.times{|i|guid<<'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_$'[rand(64)]}
It seems best to use ruby SecureRandom to generate a 128 bit UUID, like in this example (https://ruby-doc.org/stdlib-2.3.0/libdoc/securerandom/rdoc/SecureRandom.html):
SecureRandom.uuid #=> "2d931510-d99f-494a-8c67-87feb05e1594"
This UUID needs to be mapped to a string with a length of 22 characters according to this format:
1 2 3 4 5 6
0123456789012345678901234567890123456789012345678901234567890123
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_$";
I don't understand this exactly.
Should the 32-character long hex-number be converted to a 128-character long binary number, then devided in 22 sets of 6 bits(except for one that gets the remaining 2 bits?) for which each can be converted to a decimal number from 0 to 64? Which then in turn can be replaced by the corresponding character from the conversion table?
I hope someone can verify if I'm on the right track here.
And if I am, is there a computational faster way in Ruby to convert the 128 bit number to the 22 sets of 0-64 than using all these separate conversions?
Edit: For anyone having the same problem, this is my solution for now:
require 'securerandom'
# possible characters in GUID
guid64 = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_$'
guid = ""
# SecureRandom.uuid: creates a 128 bit UUID hex string
# tr('-', ''): removes the dashes from the hex string
# pack('H*'): converts the hex string to a binary number (high nibble first) (?) is this correct?
# This reverses the number so we end up with the leftover bit on the end, which helps with chopping the sting into pieces.
# It needs to be reversed again to end up with a string in the original order.
# unpack('b*'): converts the binary number to a bit string (128 0's and 1's) and places it into an array
# [0]: gets the first (and only) value from the array
# to_s.scan(/.{1,6}/m): chops the string into pieces 6 characters(bits) with the leftover on the end.
[SecureRandom.uuid.tr('-', '')].pack('H*').unpack('b*')[0].to_s.scan(/.{1,6}/m).each do |num|
# take the number (0 - 63) and find the matching character in guid64, add the found character to the guid string
guid << guid64[num.to_i(2)]
end
guid.reverse
Base64 encoding is pretty close to what you want here, but the mappings are different. No big deal, you can fix that:
require 'securerandom'
require 'base64'
# Define the two mappings here, side-by-side
BASE64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
IFCB64 = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_$'
def ifcb64(hex)
# Convert from hex to binary, then from binary to Base64
# Trim off the == padding, then convert mappings with `tr`
Base64.encode64([ hex.tr('-', '') ].pack('H*')).gsub(/\=*\n/, '').tr(BASE64, IFCB64)
end
ifcb64(SecureRandom.uuid)
# => "fa9P7E3qJEc1tPxgUuPZHm"
For no particular reason, I am trying to add a #reverse method to the Integer class:
class Integer
def reverse
self.to_s.reverse.to_i
end
end
puts 1337.reverse # => 7331
puts 1000.reverse # => 1
This works fine except for numbers ending in a 0, as shown when 1000.reverse returns 1 rather than 0001. Is there any way to keep leading zeroes when converting a string into an integer?
Short answer: no, you cant.
2.1.5 :001 > 0001
=> 1
0001 doesn't make sense at all as Integer. In the Integer world, 0001 is exactly as 1.
Moreover, the number of leading integer is generally irrelevant, unless you need to pad some integer for displaying, but in this case you are probably converting it into another kind of object (e.g a String).
If you want to keep the integer as Fixnum you will not be able to add leading zeros.
The real question is: why do you want/need leading zeros? You didn't provide such information in the question. There are probably better ways to achieve your result (such as wrapping the value into a decorator object if the goal is to properly format a result for display).
Does rjust work for you?
1000.to_s.reverse.to_i.to_s.rjust(1000.to_s.size,'0') #=> "0001"
self.to_s.to_i does convert the integer to a string and this string "0001" to an integer value. Since leading zeros are not required for regular numbers they are dropped. In other words: Keeping leading zeros does not make sense for calculations, so they are dropped. Just ask yourself how the integer 1 would look like if leading zeros would be preserved, since it represents a 32 bit number. If you need the leading zeros, there is no way around a string.
BUT 10 + "0001".to_i returns 11, so you probably need to override the + method of the String class.
I am trying to convert a hex value to a binary value (each bit in the hex string should have an equivalent four bit binary value). I was advised to use this:
num = "0ff" # (say for eg.)
bin = "%0#{num.size*4}b" % num.hex.to_i
This gives me the correct output 000011111111. I am confused with how this works, especially %0#{num.size*4}b. Could someone help me with this?
You can also do:
num = "0ff"
num.hex.to_s(2).rjust(num.size*4, '0')
You may have already figured out, but, num.size*4 is the number of digits that you want to pad the output up to with 0 because one hexadecimal digit is represented by four (log_2 16 = 4) binary digits.
You'll find the answer in the documentation of Kernel#sprintf (as pointed out by the docs for String#%):
http://www.ruby-doc.org/core/classes/Kernel.html#M001433
This is the most straightforward solution I found to convert from hexadecimal to binary:
['DEADBEEF'].pack('H*').unpack('B*').first # => "11011110101011011011111011101111"
And from binary to hexadecimal:
['11011110101011011011111011101111'].pack('B*').unpack1('H*') # => "deadbeef"
Here you can find more information:
Array#pack: https://ruby-doc.org/core-2.7.1/Array.html#method-i-pack
String#unpack1 (similar to unpack): https://ruby-doc.org/core-2.7.1/String.html#method-i-unpack1
This doesn't answer your original question, but I would assume that a lot of people coming here are, instead of looking to turn hexadecimal to actual "0s and 1s" binary output, to decode hexadecimal to a byte string representation (in the spirit of such utilities as hex2bin). As such, here is a good method for doing exactly that:
def hex_to_bin(hex)
# Prepend a '0' for padding if you don't have an even number of chars
hex = '0' << hex unless (hex.length % 2) == 0
hex.scan(/[A-Fa-f0-9]{2}/).inject('') { |encoded, byte| encoded << [byte].pack('H2') }
end
Getting back to hex again is much easier:
def bin_to_hex(bin)
bin.unpack('H*').first
end
Converting the string of hex digits back to binary is just as easy. Take the hex digits two at a time (since each byte can range from 00 to FF), convert the digits to a character, and join them back together.
def hex_to_bin(s) s.scan(/../).map { |x| x.hex.chr }.join end