Anyone able to confirm or deny the validity of this patch?
---------- Forwarded message ----------
Date: 14 Aug 2002 07:04:50 -0000
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: #18401 [Opn->Ana]: shuffle() broken
ID: 18401
Updated by: [EMAIL PROTECTED]
Reported By: [EMAIL PROTECTED]
-Status: Open
+Status: Analyzed
Bug Type: Arrays related
Operating System: Redhat 7.3
PHP Version: 4CVS-2002-08-12
New Comment:
- if (rnd_idx != cur_elem) {
- temp = elems[cur_elem];
- elems[cur_elem] = elems[rnd_idx];
+ RAND_RANGE(rnd_idx, 0, n_left, PHP_RAND_MAX);
+ if (rnd_idx != n_left) {
+ temp = elems[n_left];
+ elems[n_left] = elems[rnd_idx];
elems[rnd_idx] = temp;
Thanks for detailed report. This diff clearly show where to fix.
Swapping values requires 3 lines!!
Previous Comments:
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[2002-08-12 03:10:28] [EMAIL PROTECTED]
I have just tried it with the latest CVS and I still get the same
results. Brad's changes were in a different section of the file.
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[2002-08-11 02:30:52] [EMAIL PROTECTED]
I'm pretty Brad has been playing with this code. Can you test again,
and report back with a new snapshot?
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[2002-07-18 01:03:51] [EMAIL PROTECTED]
The shuffle() function in the CVS is (still) broken. It does not
correctly generate all possible combinations of the array. (I know this
function was recently updated, this test is with new version.)
Here is a diff to fix the problem:
--- array.c Thu Jul 18 00:50:54 2002
+++ array.new.c Thu Jul 18 00:49:35 2002
@@ -1441,7 +1441,7 @@
{
Bucket **elems, *temp;
HashTable *hash;
- int j, n_elems, cur_elem = 0, rnd_idx, n_left;
+ int j, n_elems, rnd_idx, n_left;
n_elems = zend_hash_num_elements(Z_ARRVAL_P(array));
@@ -1457,13 +1457,12 @@
elems[j++] = temp;
while (--n_left) {
rnd_idx = php_rand(TSRMLS_C);
- RAND_RANGE(rnd_idx, cur_elem, n_left, PHP_RAND_MAX);
- if (rnd_idx != cur_elem) {
- temp = elems[cur_elem];
- elems[cur_elem] = elems[rnd_idx];
+ RAND_RANGE(rnd_idx, 0, n_left, PHP_RAND_MAX);
+ if (rnd_idx != n_left) {
+ temp = elems[n_left];
+ elems[n_left] = elems[rnd_idx];
elems[rnd_idx] = temp;
}
- cur_elem++;
}
HANDLE_BLOCK_INTERRUPTIONS();
Here is some PHP that will reproduce the problem. As you can see the
built-in shuffle() only generates 3 of the 6 possible combinations,
while the userland array_shuffle() correctly generates all 6 with equal
likelyhood.
<?php
function array_shuffle(&$array) {
$i = count($array);
while (--$i) {
$j = mt_rand(0, $i);
if ($i != $j) {
/* swap elements */
$tmp = $array[$j];
$array[$j] = $array[$i];
$array[$i] = $tmp;
}
}
}
function test($function) {
$a = array();
for ($i = 0; $i < 10000; $i++) {
$p = range(1,3);
$function($p);
$s = join('', $p);
$a[$s]++;
}
print "$function\n";
foreach($a as $k => $v) {
print "$k: $v\n";
}
}
test('shuffle');
test('array_shuffle');
?>
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--
Edit this bug report at http://bugs.php.net/?id=18401&edit=1
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