will output a 32-character hexadecimal number just like guid. The difference is that guid is randomly generated, and md5 needs to be generated based on the input data.
Advantages: The output value can be controlled based on the input seed data. If the seed The data is regular and non-repeating, and md5 can be used to protect the data, resulting in great confusion.
Disadvantages: 32-bit characters are too long; non-duplicate seed data needs to be provided;
Usage: High concurrency, with seconds as the seed data, duplication will still occur.
For our purposes, uniqid() is like an improved version of md5(). In particular, we can use differential identifiers as string prefixes, which can reduce the chance of repeated naming.
For extreme situations such as non-high concurrency, it is recommended to use this function, which can already meet general needs.
Definition: The uniqid() function generates a unique ID based on the current time in microseconds.
Explanation: prefix can add a prefix to the output string. The example is as follows. When the more_entropy parameter is true, a 23-bit string will be output.
var_dump(uniqid());
var_dump (uniqid("a"));
?>
The output result is:
string(13) "51734aa562254" string(14) "a51734aa562257"
Advantages: 13-bit string length is an acceptable file naming length; prefixes can be added, and the result contains data Obfuscation can avoid reverse inference of original data.
Disadvantages: Similar to md5, high concurrency, using seconds as the seed data, duplication will still occur.
3. Upgraded version plan:
1, fast_uuid: returns 17 digits
It is a bit like an incomplete customized version of uniqid(), the "seed number start time" that appears in this function "The concept is inspiring.
The default time used in time() and uniqid() is calculated from 1970, and the length is ten digits (1366512439). Using the "seed number start time" can reduce this value, because we actually need Yes, it is just a value that can grow automatically.
After customizing the starting time, in addition to reducing the length, it can also play a role in confusion.
Copy code The code is as follows:
/*
* The parameter suffix_len specifies how many random digits are appended to the generated ID value , the default value is 3.
* Thanks to "Ivan Tan | Tan Junqing DrinChing (at) Gmail.com" for providing the algorithm.
* @param int suffix_len
* @return string
*/
function fast_uuid($suffix_len=3){
//! The starting time for calculating the seed number
$being_timestamp = strtotime('2013-3-21');
$time = explode(' ', microtime());
$id = ($time[1] - $being_timestamp) . sprintf(' %06u', substr($time[0], 2, 6));
if ($suffix_len > 0)
{
$id .= substr(sprintf('%010u', mt_rand ()), 0, $suffix_len);
}
return $id;
}
Output,
29832412631099013
2, time()+random Number:
In the above example, random numbers have been used to solve multiple requests that occur in one second. Provide two functions as follows,
Copy code The code is as follows:
function random($length ) {
$hash = '';
$chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz';
$max = strlen($chars) - 1;
PHP_VERSION < '4.2.0 ' && mt_srand(( double)microtime() * 1000000);
for($i = 0; $i < $length; $i++) {
$hash .= $chars[mt_rand(0, $max)];
}
return $hash;
}
function random2($length, $numeric = 0) {
PHP_VERSION < '4.2.0' ? mt_srand((double)microtime() * 1000000) : mt_srand();
$seed = base_convert(md5(print_r($_SERVER, 1).microtime()), 16, $numeric ? 10 : 35);
$seed = $numeric ? ( str_replace('0', '', $seed).'012340567890') : ($seed.'zZ'.strtoupper($seed));
$hash = '';
$max = strlen( $seed) - 1;
for($i = 0; $i < $length; $i++) {
$hash .= $seed[mt_rand(0, $max)];
}
Return $hash;
}
?>
4. Final solution :
Idea: userid+seconds+random number. Among them, "userid+second" is converted from decimal to 64, reducing the number of digits;
Description:
userid: The maximum value of "ZZZZ" in 64 is converted to decimal equal to "16777215", and the maximum value of "ZZZ" is converted to decimal The value is equal to "262143";
Seconds: Set your own time starting point.
$less=time()-strtotime('2012-4-21′); Convert to hexadecimal "1SpRe", 5 digits
$less=time()-strtotime('2013-3-21 ′); Convert to hexadecimal "_jHY"; 4-digit
random number: use random(3) to generate 3-digit random number;
final result:
4-digit userid+4-digit second + 3-digit Random number = 11-digit string. Although the results look similar to uniqid(), the robustness is improved.
5. Decimal to hexadecimal conversion algorithm:
Algorithm 1:
Copy code The code is as follows:
const KeyCode = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_$';
/**
* Convert a 64-digit string to a decimal string
* @param $m string 64-digit string
* @param $len integer Returns the length of the string , if the length is not enough, fill it with 0, 0 means no padding
* @return string
* @author 马野
*/
function hex64to10($m, $len = 0) {
$m = (string)$m;
$hex2 = '';
$Code = KeyCode;
for($i = 0, $l = strlen($Code); $i < $l; $i++) {
$KeyCode[] = $Code[$i];
}
$KeyCode = array_flip($KeyCode);
for($i = 0, $l = strlen($m); $i < $l; $i++) {
$one = $m[$i];
$hex2 .= str_pad(decbin($KeyCode[$one]), 6, '0', STR_PAD_LEFT);
}
$return = bindec($hex2);
if($len) {
$clen = strlen($return);
if($clen >= $len) {
return $return;
}
else {
return str_pad($return, $len, '0', STR_PAD_LEFT);
}
}
return $return;
}
/**
* Convert the decimal numeric string to a 64-digit numeric string
* @param $m string Decimal numeric string
* @param $len integer Returns the string length , if the length is not enough, fill it with 0, 0 means no padding
* @return string
* @author 马野
*/
function hex10to64($m, $len = 0) {
$KeyCode = KeyCode;
$hex2 = decbin($m);
$hex2 = str_rsplit($hex2, 6);
$hex64 = array();
foreach($hex2 as $one) {
$t = bindec($one);
$hex64[] = $KeyCode[$t];
}
$return = preg_replace('/^0*/', '', implode('', $hex64));
if($len) {
$clen = strlen($return);
if($clen >= $len) {
return $return;
}
else {
return str_pad($return, $len, '0', STR_PAD_LEFT);
}
}
return $return;
}
/**
* Convert hexadecimal number string to hexadecimal number string
* @param $m string Hexadecimal number string
* @param $len integer Returns the string length , if the length is not enough, fill it with 0, 0 means no padding
* @return string
* @author 马野
*/
function hex16to64($m, $len = 0) {
$KeyCode = KeyCode;
$hex2 = array();
for($i = 0, $j = strlen($m); $i < $j; ++$i) {
$hex2[] = str_pad(base_convert($m[$i], 16, 2), 4, '0', STR_PAD_LEFT);
}
$hex2 = implode('', $hex2);
$hex2 = str_rsplit($hex2, 6);
foreach($hex2 as $one) {
$hex64[] = $KeyCode[bindec($one)];
}
$return = preg_replace('/^0*/', '', implode('', $hex64));
if($len) {
$clen = strlen($return);
if($clen >= $len) {
return $return;
}
else {
return str_pad($return, $len, '0', STR_PAD_LEFT);
}
}
return $return;
}
/**
* The function is similar to the PHP native function str_split, except that the cutting starts from the end
* @param $str string The string to be cut
* @param $len integer The length of each string
* @return array
* @author 马野
*/
function str_rsplit($str, $len = 1) {
if($str == null || $str == false || $str == '') return false;
$strlen = strlen($str);
if($strlen <= $len) return array($str);
$headlen = $strlen % $len;
if($headlen == 0) {
return str_split($str, $len);
}
$return = array(substr($str, 0, $headlen));
return array_merge($return, str_split(substr($str, $headlen), $len));
}
$a=idate("U");
echo "rn
e:" . hex10to64($a);
echo "rn
e:" . hex64to10(hex10to64($a));
算法2：
复制代码 代码如下:
function dec2s4($dec) {
$base = '0123456789_$abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$result = '';
do {
$result = $base[$dec % 64] . $result;
$dec = intval($dec / 64);
} while ($dec != 0);
return $result;
}
function s42dec($sixty_four) {
$base_map = array ( '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4, '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9, '_' => 10, '$' => 11, 'a' => 12, 'b' => 13, 'c' => 14, 'd' => 15, 'e' => 16, 'f' => 17, 'g' => 18, 'h' => 19, 'i' => 20, 'j' => 21, 'k' => 22, 'l' => 23, 'm' => 24, 'n' => 25, 'o' => 26, 'p' => 27, 'q' => 28, 'r' => 29, 's' => 30, 't' => 31, 'u' => 32, 'v' => 33, 'w' => 34, 'x' => 35, 'y' => 36, 'z' => 37, 'A' => 38, 'B' => 39, 'C' => 40, 'D' => 41, 'E' => 42, 'F' => 43, 'G' => 44, 'H' => 45, 'I' => 46, 'J' => 47, 'K' => 48, 'L' => 49, 'M' => 50, 'N' => 51, 'O' => 52, 'P' => 53, 'Q' => 54, 'R' => 55, 'S' => 56, 'T' => 57, 'U' => 58, 'V' => 59, 'W' => 60, 'X' => 61, 'Y' => 62, 'Z' => 63, );
$result = 0;
$len = strlen($sixty_four);
for ($n = 0; $n < $len; $n++) {
$result *= 64;
$result += $base_map[$sixty_four{$n}];
}
return $result;
}
$a=idate("U");
var_dump(dec2s4($a));
var_dump(s42dec(dec2s4($a)));
算法效率测试：
复制代码 代码如下:
$strarr = array();
$time1 = microtime(true);
for($i = 0; $i < 10000; ++$i) {
$str = idate("U")+$i;
$strarr[] = "{$i}->$strrn
";
}
$time2 = microtime(true);
$time3 = $time2 - $time1;
$time1 = microtime(true);
for($i = 0; $i < 10000; ++$i) {
$str = dec2s4(idate("U")+$i);
$strarr[] = "{$i}->$strrn
";
}
$time2 = microtime(true);
echo "rn
运行10000次用时（秒）：" . ($time2 - $time1 - $time3);
Test results
Algorithm 1: 0.1687250137329
Algorithm 2: 0.044965028762817
Conclusion: Although Algorithm 1 is less efficient, it can convert the hexadecimal generated by md5 into hexadecimal and can be used in The string must be shortened in an md5 environment.
6. Summary
This article involves several methods that can be used to rename uploaded images. The key point is to use decimal to hexadecimal to reduce the string.
For example, the 17-digit number generated by fast_uuid is converted into hexadecimal with only 7 characters;
The specific use can be used flexibly according to your own situation. I hope it will be helpful to everyone.
http://www.bkjia.com/PHPjc/825004.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/825004.htmlTechArticle1. Applicable scenarios: You cannot use the self-increasing number returned from the database to rename the uploaded image. This is determined by the process of uploading images or files. General image upload processing process...
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
