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Re: rand() function on Windows systems
by BrowserUk (Patriarch) on Dec 30, 2016 at 20:32 UTC
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If you install Inline::C you can access the MS CRT rand() & srand() and wrap them in your own wrappers.
The following code produces 56 (which is the same as I get from Perl's built-ins for 5.10). You might try it on your system and see how it compares:
#! perl -slw
use strict;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C', NAME => 'junk1_IC', CLEAN_AFTER_BUILD => 0
+;
int osrand( SV *seed ) {
srand( (unsigned int)SvIV( seed ) );
return 1;
}
double orand( SV *max ) {
return (double)rand() / 32767.0 * SvNV( max );
}
END_C
osrand( 555 );
print int orand( 1000 );
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
In the absence of evidence, opinion is indistinguishable from prejudice.
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Yes. That did the trick.
Thank you BrowserUk
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{
my $seed;
sub ppSrand{ $seed = int( $_[ 0 ] & 32767 ); }
sub ppRand{
my $max = shift // 1;
$seed = ( $seed * 214013 + 2531011 );
return ( ( $seed >> 16 ) & 32767 ) / 32768 * $max; ## Amend
+ed per post below.
}
}
ppSrand( 555 );
print int ppRand( 1000 );
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
In the absence of evidence, opinion is indistinguishable from prejudice.
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Re: rand() function on Windows systems
by LanX (Sage) on Dec 30, 2016 at 19:58 UTC
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From perl5200delta#rand-now-uses-a-consistent-random-number-generator
- rand now uses a consistent random number generator
Previously perl would use a platform specific random number generator, varying between the libc rand(), random() or drand48().
This meant that the quality of perl's random numbers would vary from platform to platform, from the 15 bits of rand() on Windows to 48-bits on POSIX platforms such as Linux with drand48().
Perl now uses its own internal drand48() implementation on all platforms. This does not make perl's rand cryptographically secure. perl #115928
If you are desperate enough, try calling the original 15 bits windows version.
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Re: rand() function on Windows systems
by Laurent_R (Canon) on Dec 30, 2016 at 20:28 UTC
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So, in essence, you want your random numbers not to be random, that's a kind of oxymoron.
Running your code on my Windows box, with ActiveState Perl v5.16.3, I get 56:
C:\Users\Laurent>perl -e "srand(555); my $range = 1000; my $number = i
+nt(rand($range)); print $number ;"
56
On the same Windows platform, running Perl v5.14.4 under Cygwin, I get 466:
Laurent@Laurent-HP ~
$ perl -e 'srand(555);
> my $range = 1000;
> my $number = int(rand($range));
> print $number,"\n";'
466
If you really need the same pseudo-random numbers as on you old Perl version, then run your old Perl version, write the pseudo-numbers generated to a file and use the numbers in this file on your new version.
But the bottom line is, IMHO, that you should probably not try to rely on a random number generator to give you always the same sequence of numbers.
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> to give you always the same sequence of numbers.
But this IS documented behavior, see srand
The point is rather that you can't guarantee the same sequence for newer Perl versions because this would inhibit any progress.
Progress like being OS independent.
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But this IS documented behavior, see srand
Yes, Rolf, agreed. I know that if you initialize srand with a specific number, you'll be able to get repeatedly the same sequence from rand if you run it several times on the same machine with the same Perl version. This is not specific to perl, many programming languages have the same feature. And this is useful especially for some testing purposes (e.g. to be able to test the same conditions several times).
But I said: "you should probably not try to rely on a random number generator to give you always the same sequence of numbers." The word always is important in what I meant. One should not expect the same sequence forever.
And the possible solution I suggested relies on that: if you need the same sequence of pseudo-random integers with different Perl versions and platforms, for whatever reason,, then store that sequence somewhere and re-use it.
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I also got 56 on ActiveState 5.16 (and BrowserUK also, apparently), but the OP seems to be looking for 52:
older versions of Perl output a number of 52
I wonder which version of Perl was being used then.
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Re: rand() function on Windows systems
by ikegami (Patriarch) on Jan 03, 2017 at 17:03 UTC
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If you want a specific sequence from rand, override *CORE::GLOBAL::rand with a sub that returns the series you wish to receive.
BEGIN {
my @seq = ...;
*CORE::GLOBAL::rand = sub { shift(@seq) };
}
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Re: rand() function on Windows systems
by LanX (Sage) on Dec 30, 2016 at 19:14 UTC
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