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Date: Wed, 16 Jul 2014 14:13:54 +0900
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Subject: Use of php_mt_rand() rather than php_rand()
From: yohgaki@ohgaki.net (Yasuo Ohgaki)

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Hi all,

There are few places that uses php_rand() currently.

https://bugs.php.net/bug.php?id=66718
http://lxr.php.net/search?q=php_rand&defs=&refs=&path=&hist=&project=PHP_5_5

These functions could use php_mt_rand() instead of php_rand().

php_rand() uses several rand functions

62PHPAPI long php_rand(TSRMLS_D)
63{
64    long ret;
65
66    if (!BG(rand_is_seeded)) {
67        php_srand(GENERATE_SEED() TSRMLS_CC);
68    }
69
70#ifdef ZTS
71    ret = php_rand_r(&BG(rand_seed));
72#else
73# if defined(HAVE_RANDOM)
74    ret = random();
75# elif defined(HAVE_LRAND48)
76    ret = lrand48();
77# else
78    ret = rand();
79# endif
80#endif
81
82    return ret;
83}

Most systems use random() which has cycle of 16 * ((2^31) - 1),
while MT rand has 2^19937-1.

php_mt_rand() could be used where php_rand() is used. Unlike php_rand(),
php_mt_rand() does not check if it is seeded or not. It should be changed
to check seed status.

The only BC issue I can think of is game that expects the same pseudo
random sequences. These apps may use mt_srand() to get fixed random
sequences and adjust their apps if it is needed. This is acceptable BC
for new releases. IMO.

It would be good idea to support 64bit version of MT on 64bit platforms,
too.

http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt64.html

Any comments?

--
Yasuo Ohgaki
yohgaki@ohgaki.net

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