Re: Random Numbers under XP: Translating XS to Win32::API

[BrowserUk]

Are you having problems? :)

There is no entrypoint 'RtlGenRandom' exported from advapi32.dll. The function documented under that name is exported as 'SystemFunction36' (and may go away in future versions).

#! perl -slw
use strict;

sub random {
    my $count = shift;
    use Win32::API::Prototype;
    ApiLink( 'ADVAPI32.DLL', 'BOOLEAN SystemFunction036( PVOID b, ULON
+G n )' )
        or die $^E;

    our $RtlGenRandom;
    *RtlGenRandom = *SystemFunction036;

    my $buffer = chr( 0 ) x ( 4 * $count );
    if( RtlGenRandom( $buffer, 4 * $count ) ) {
        return [ unpack 'V*', $buffer ];
    }
    else {
        warn "rtlGenRandom failed : $^E";
        return;
    }
}

print for @{ random( 10 ) };
__END__
P:\test>471107
Name "main::SystemFunction036" used only once: possible typo at P:\tes
+t\471107.pl line 11.
2938396619
3012541328
434618806
2806772272
1411585649
1621144589
2620908003
1934412219
3486653462
3699174573

[jdhedden]

Super! That's just what I needed.

I'll probably eliminate the use of the function 'renaming', and just call SystemFunction036 (with appropriate comments for clarity).

I noted your use of the 'V*' directive for the unpack call. Although with random data, distinguishing between big-endian and little-endian is superfluous.

Thanks for the code!

[BrowserUk]

I noted your use of the 'V*' directive for the unpack call. Although with random data, distinguishing between big-endian and little-endian is superfluous.

True, but as the platform is little-endian, converting using V* rather than N* saves doing a lot of fiddly byte and bit-twiddling. This really shows up when you unpack a few thousand ulongs.

Below I timed unpacking the same 1000 values both ways:

P:\test>471107
Name "main::SystemFunction036" used only once: possible typo at P:\tes
+t\471107.pl line 14.
  1 trial  of N* non-native BigEndian (  1.848ms total), 1.848ms/trial

  1 trial  of  V* native LittleEndian (    310us total), 310us/trial

It essentially is the difference between doing nothing and doing something (fiddly).