根据PHP中的字符串在范围内生成固定的随机数

Question

I need to generate a random number or hash that will be the same each time based on a string. This is done easily enough with the function crc32, however, I need it to be an integer between a range because the random number will be picking an item out of an array.

Here's the code I have so far:

$min=0;
$max=count($myarray);
$number = crc32("Joe Jones");

$rnd = '.'.(string)$number;
//(Int((max-min+1)*Rnd+min))
$rand = round(($max-$min+1)*$rnd+$min);

echo $rand;

It seems to work, but it always picks lower numbers. It never picks the higher numbers.

Answer 1

Just use mod (%). $x % $n will ensure an output between 0 and $n-1 for any $x .

$myArray=range(1,1000);
$max=count($myArray); //1000
$number = crc32("Joe Jones"); //2559948711
$rand=$number % $max; //711

Also just a note about crc32: It may return a negative number if you run it on a 32 bit platform, so you may optionally want to do abs(crc32($input))

Answer 2

Your crc32 function is producing a negative number. Change the line as follows:

$number = abs(crc32("Joe Jones"));

This turns that negative number in to a positive one. Also, you might want to consider multiplying that number if your your array count is is low. How high that goes is up to you.