I need to convert a random text to a number. But the ramdom text has always to be converted to the same number. For example:
xxxx -> 10
testing -> 396
stackoverflow -> 72
I cant use the number of characters to convert the string cause if I have 2 strings with the same number characters they need to have a different number (at most times at least).
I do not need to have this number in a range. No! It can be any number, since it will always be the same given a certain string.
You could try using hashes (md5, sha1, etc):
$number = hexdec( md5("hello world") );
$number = hexdec( sha1("hello world") );
Hashes of the same string will transform to the same number.
What about;
$number = crc32($string);
Should be cheap, gives integer output, and produce reasonable randomness for your use case.
Other methods that have been shown have the potential of having collisions. The following should not.
$num = "";
for($i = 0; $i < strlen($str); $i++)
$num .= str_pad(ord($str[$i]), 3 "0", STR_PAD_LEFT);
return $num;
Related
I have many strings. Each string something like:
"i_love_pizza_123"
"whatever_this_is_now_later"
"programming_is_awesome"
"stack_overflow_ftw"
...etc
I need to be able to convert each string to a random number, 1-10. Each time that string gets converted, it should consistently be the same number. A sampling of strings, even with similar text should result in a fairly even spread of values 1-10.
My first thought was to do something like md5($string), then break down a-f,0-9 into ten roughly-equal groups, determine where the first character of the hash falls, and put it in that group. But doing so seems to have issues when converting 16 down to 10 by multiplying by 0.625, but that causes the spread to be uneven.
Thoughts on a good method to consistently convert a string to a random/repeatable number, 1-10? There has to be an easier way.
Here's a quick demo how you can do it.
function getOneToTenHash($str) {
$hash = hash('sha256', $str, true);
$unpacked = unpack("L", $hash); // convert first 4 bytes of hash to 32-bit unsigned int
$val = $unpacked[1];
return ($val % 10) + 1; // get 1 - 10 value
}
for ($i = 0; $i < 100; $i++) {
echo getOneToTenHash('str' . $i) . "\n";
}
How it works:
Basically you get the output of a hash function and downscale it to desired range (1..10 in this case).
In the example above, I used sha256 hash function which returns 32 bytes of arbitrary binary data. Then I extract just first 4 bytes as integer value (unpack()).
At this point I have a 4 bytes integer value (0..4294967295 range). In order to downscale it to 1..10 range I just take the remainder of division by 10 (0..9) and add 1.
It's not the only way to downscale the range but an easy one.
So, the above example consists of 3 steps:
get the hash value
convert the hash value to integer
downscale integer range
A much shorter example with crc32() function which returns integer value right away thus allowing us to omit step 2:
function getOneToTenHash($str) {
$int = crc32($str); // 0..4294967295
return ($int % 10) + 1; // 1..10
}
below maybe what u want
$inStr = "hello world";
$md5Str = md5($inStr);
$len = strlen($md5Str);
$out = 0;
for($i=0; $i<$len; $i++) {
$out = 7*$out + intval($md5Str[$i]); // if you want more random, can and random() here
}
$out = ($out % 10 + 9)%10; // scope= [1,10]
Is there a term for the idea of storing large numbers as letters? For example let's say I have the (relatively small) number 138201162401719 and I want to shrink the number of characters (I know this does not help with saving disk space) to the fewest possible number of characters. There are 26 letters in the English alphabet (but i count them as 25 since we need a zero letter). If I start splitting up my large number into pieces that are each 25 or less I get:
13, 8, 20, 11, 6, 24, 0, 17, 19
If I then count the numbers of the alphabet a=0, b=1, c=2, d=3... I can convert this to:
NIULGYART
So I went from 15 digits long (138201162401719) to 9 characters long (NIULGYART). This could of course be easily converted back to the original number as well.
So...my first question is "Does this have a name" and my second "Does anyone have PHP code that will do the conversion (in both directions)?"
I am looking for proper terminology so that I can do my own research in Google...though working code examples are cool too.
This only possible if you're considering to store your number before processing as a string. Because you can't store huge number as integers. You will lost the precision (13820116240171986468445 will be stored as 1.3820116240172E+22) so the alot of digits are lost.
If you're considering storing the number as a string this will be your answer:
Functions used: intval, chr and preg_match_all.
<?php
$regex = '/(2[0-5])|(1[0-9])|([0-9])/';
$numberString = '138201162401719';
preg_match_all($regex, $numberString, $numberArray, PREG_SET_ORDER);
echo($numberString . " -> ");
foreach($numberArray as $value){
$character = chr (intval($value[0]) + 65);
echo($character);
}
?>
Demo
This is the result:
138201162401719 -> NIULGYART
Here's how I would do it:
Store the big number as a string and split it into an array of numbers containing one digit each
Loop through the array extract 2-digit chunks using substr()
Check if the number is less than 26 (in which case, it is an alphabet) and add them to an array
Use array_map() with chr() to create a new array of characters from the above array
Implode the resulting array to get the cipher
In code:
$str = '138201162401719';
$arr = str_split($str);
$i = 0; // starting from the left
while ($i < count($arr)) {
$n = substr($str, $i, 2);
$firstchar = substr($n, 0, 1);
if ($n < 26 && $firstchar != 0) {
$result[] = substr($str, $i, 2);
$i += 2; // advance two characters
} else {
$result[] = substr($str, $i, 1);
$i++; // advance one character
}
}
$output = array_map(function($n) {
return chr($n+65);
}, $result);
echo implode($output); // => NIULGYART
Demo.
As an alternative, you could convert the input integer to express it in base 26, instead of base 10. Something like (pseudocode):
func convertBase26(num)
if (num < 0)
return "-" & convertBase26(-num) // '&' is concatenate.
else if (num = 0)
return "A"
endif
output = "";
while (num > 0)
output <- ('A' + num MOD 26) & output // Modulus operator.
num <- num DIV 26 // Integer division.
endwhile
return output
endfunc
This uses A = 0, B = 1, up to Z = 25 and standard place notation: 26 = BA. Obviously a base conversion is easily reversible.
strtr() is a magnificent tool for this task! It replaces the longest match as is traverses the string.
Code: (Demo)
function toAlpha ($num) {
return strtr($num, range("A", "Z"));
}
$string = toAlpha("138201162401719");
echo "$string\n";
$string = toAlpha("123456789012345");
echo "$string\n";
$string = toAlpha("101112131415161");
echo "$string\n";
$string = toAlpha("2625242322212019");
echo "$string";
Output:
NIULGYART
MDEFGHIJAMDEF
KLMNOPQB
CGZYXWVUT
Just flip the lookup array to reverse the conversion: https://3v4l.org/YsFZu
Merged: https://3v4l.org/u3NQ5
Of course, I must mention that there is a vulnerability with converting a sequence of letters to numbers and back to letters. Consider BB becomes 11 then is mistaken for eleven which would traslate to L when converted again.
There are ways to mitigate this by adjusting the lookup array, but that may not be necessary/favorable depending on program requirements.
And here is another consideration from CodeReview.
I have been trying to do the same thing in PHP without success.
Assuming I'm using the 26 letters of the English alphabet, starting with A = 0 down to Z as 25:
I find the highest power of 26 lower than the number I am encoding. I divide it by the best power of 26 I found. Of the result I take away the integer, convert it to a letter and multiply the decimals by 26. I keep doing that until I get a whole number. It's ok to get a zero as it's an A, but if it has decimals it must be multiplied.
For 1 billion which is DGEHTYM and it's done in 6 loops obviously. Although my answer demonstrates how to encode, I'm afraid it does not help doing so on PHP which is what I'm trying to do myself. I hope the algorithm helps people out there though.
How can I separate a number and get the first two digits in PHP?
For example: 1345 -> I want this output=> 13 or 1542 I want 15.
one possibility would be to use substr:
echo substr($mynumber, 0, 2);
EDIT:
please not that, like hakre said, this will break for negative numbers or small numbers with decimal places. his solution is the better one, as he's doing some checks to avoid this.
First of all you need to normalize your number, because not all numbers in PHP consist of digits only. You might be looking for an integer number:
$number = (int) $number;
Problems you can run in here is the range of integer numbers in PHP or rounding issues, see Integers Docs, INF comes to mind as well.
As the number now is an integer, you can use it in string context and extract the first two characters which will be the first two digits if the number is not negative. If the number is negative, the sign needs to be preserved:
$twoDigits = substr($number, 0, $number < 0 ? 3 : 2);
See the Demo.
Shouldn't be too hard? A simple substring should do the trick (you can treat numbers as strings in a loosely typed language like PHP).
See the PHP manual page for the substr() function.
Something like this:
$output = substr($input, 0, 2); //get first two characters (digits)
You can get the string value of your number then get the part you want using
substr.
this should do what you want
$length = 2;
$newstr = substr($string, $lenght);
With strong type-hinting in new version of PHP (> PHP 7.3) you can't use substr on a function if you have integer or float. Yes, you can cast as string but it's not a good solution.
You can divide by some ten factor and recast to int.
$number = 1345;
$mynumber = (int)($number/100);
echo $mynumber;
Display: 13
If you don't want to use substr you can divide your number by 10 until it has 2 digits:
<?php
function foo($i) {
$i = abs((int)$i);
while ($i > 99)
$i = $i / 10;
return $i;
}
will give you first two digits
So I was wonder what are some good/preferred methods for generating a 'hex-like' value in PHP? Preferably, I would want to restrict it to 5 characters long like such: 1e1f7
Currently this is what I am doing:
echo dechex(mt_rand(10000, 99999));
however this gives me values anywhere from 4-5 characters long, and I want to keep it at a consistent 4 or 5.
What are some ways to better generate something like this in PHP? Is there even a built in function?
Note: When I say 'hex-like' I really just mean a random combination of letters and numbers. There does not have to be a restriction on available letters.
Something simple like:
$length = 5;
$string = "";
while ($length > 0) {
$string .= dechex(mt_rand(0,15));
$length -= 1;
}
return $string;
(untested)
Or fix your mt_rand range to: mt_rand(65535, 1048575) (10000-fffff in hex) or if you like tinfoil hats: mt_rand(hexdec("10000"), hexdec("ffffff"))
The advantage of the while-loop approach is that it works for arbitrarily long strings. If you'd want 32 random characters you're well over the integer limit and a single mt_rand will not work.
If you really just want random stuff, I'd propose:
$length = 5;
$string = "";
$characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-=+!##$%^&*()[]"; // change to whatever characters you want
while ($length > 0) {
$string .= $characters[mt_rand(0,strlen($characters)-1)];
$length -= 1;
}
return $string;
(untested)
echo substr( base64_encode( mt_rand(1000, mt_getrandmax() ), 0, 5);
This uses more of the alphabet due to the base64, but remember that it will include upper and lower case letters along with numbers.
Why all the work sha1 is tested and evenly distributed:
substr(sha1(uniqid('moreentropyhere')),0,5);
I have used this to generate millions and millions of uniq uids for sharding tables, no collisions and remarkably evenly distributed regardless of the length you use...
you can even use binary form of sha1 hash for base 64:
base64_encode(sha1(uniqid('moreentropyhere'), true))
to limit characters, you can use a regex:
substr(preg_replace('~[^a-km-np-z2-9]~','',strtolower(base64_encode(sha1(uniqid(),true)))),0,6)
Here we limited 0,1,l (letter), and o (letter) from the string, trading a little entropy to prevent confusion (and service tickets) during entry for all ages...
I have some strings containing alpha numeric values, say
asdf1234,
qwerty//2345
etc..
I want to generate a specific constant number related with the string. The number should not match any number generated corresponding with other string..
Does it have to be a number?
You could simply hash the string, which would give you a unique value.
echo md5('any string in here');
Note: This is a one-way hash, it cannot be converted from the hash back to the string.
This is how passwords are typically stored (using this or another hash function, typically with a 'salt' method added.) Checking a password is then done by hashing the input and comparing to the stored hash.
edit: md5 hashes are 32 characters in length.
Take a look at other hash functions:
http://us3.php.net/manual/en/function.crc32.php (returns a number, possibly negative)
http://us3.php.net/manual/en/function.sha1.php (40 characters)
You can use a hashing function like md5, but that's not very interesting.
Instead, you can turn the string into its sequence of ASCII characters (since you said that it's alpha-numeric) - that way, it can easily be converted back, corresponds to the string's length (length*3 to be exact), it has 0 collision chance, since it's just turning it to another representation, always a number and it's a little more interesting... Example code:
function encode($string) {
$ans = array();
$string = str_split($string);
#go through every character, changing it to its ASCII value
for ($i = 0; $i < count($string); $i++) {
#ord turns a character into its ASCII values
$ascii = (string) ord($string[$i]);
#make sure it's 3 characters long
if (strlen($ascii) < 3)
$ascii = '0'.$ascii;
$ans[] = $ascii;
}
#turn it into a string
return implode('', $ans);
}
function decode($string) {
$ans = '';
$string = str_split($string);
$chars = array();
#construct the characters by going over the three numbers
for ($i = 0; $i < count($string); $i+=3)
$chars[] = $string[$i] . $string[$i+1] . $string[$i+2];
#chr turns a single integer into its ASCII value
for ($i = 0; $i < count($chars); $i++)
$ans .= chr($chars[$i]);
return $ans;
}
Example:
$original = 'asdf1234';
#will echo
#097115100102049050051052
$encoded = encode($original);
echo $encoded . "\n";
#will echo asdf1234
$decoded = decode($encoded);
echo $decoded . "\n";
echo $original === $decoded; #echoes 1, meaning true
You're looking for a hash function, such as md5. You probably want to pass it the $raw_output=true parameter to get access to the raw bytes, then cast them to whatever representation you want the number in.
A cryptographic hash function will give you a different number for each input string, but it's a rather large number — 20 bytes in the case of SHA-1, for example. In principle it's possible for two strings to produce the same hash value, but the chance of it happening is so extremely small that it's considered negligible.
If you want a smaller number — say, a 32-bit integer — then you can't use a hash function because the probability of collision is too high. Instead, you'll need to keep a record of all the mappings you've established. Make a database table that associates strings with numbers, and each time you're given a string, look it up in the table. If you find it there, return the associated number. If not, choose a new number that isn't used by any of the existing records, and add the new string and number to the table.