Use Config and check the ivsize key:

C:\test>perl -MConfig -E"say $Config{ ivsize }"
8

C:\test>\perl32\bin\perl -MConfig -le"print $Config{ ivsize }"
4
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Thx, but if I can avoid loading Config, and the dependency on it, then pure Perl wins.

root@raspberry2:/home/helmut# time perl -MConfig -E 'print $Config{ivs
+ize};'
8
real    0m0.177s
user    0m0.160s
sys    0m0.010s
root@raspberry2:/home/helmut# time perl -e  'print length(pack('j', -1
+))*8;'
64
real    0m0.028s
user    0m0.020s
sys    0m0.000s
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Config is a core module, so is always available.

Your code seems to work fine here:

C:\test>\perl32\bin\perl -e"print length(pack('j', -1))*8;"
32
C:\test>perl -e"print length(pack('j', -1))*8;"
64
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---

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.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Config is part of Perl, and is Pure Perl.

I think so. Perhaps, it is also an option for you to ask perl itself with the help of core module Config?

 perl -e 'use Config; print $Config{use64bitint} eq "define" ? "yes, "
+ : "not ", "64bit perl\n"'
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Result (here):

yes, 64bit perl
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For that kind of inquiry, perl has extended use for the -V option, supporting regular expressions et all:

$ perl -V:'use64bit(int|all)|[iu]vsize'
ivsize='8';
use64bitall='define';
use64bitint='define';
uvsize='8';
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Enjoy, Have FUN! H.Merijn

log(~0)/log(2)
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Beautiful use of the Maths. ;)




Dave

*cough*

$ perl -E " say  log(~0)/log(2) "
31.9999999996641

$ perl -E " say  int 0.999+log(~0)/log(2) "
32
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log(~0)/log(2)
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Hmm, I tried a similar idea (get the index of the highest bit), but it failed. Now I remember:

helmut@w3:~$ perl -e 'print log(-1)/log(2),"\n";'
Can't take log of -1 at -e line 1.
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Thx, this is extremely fast and IMHO reliable, because it tests the capabilty directly.

Helmut "wollmers" Wollmersdorfer

I figure for base2 stuff length is better than log (no need to worry about rounding/transcendental crap), e.g.,

4*length sprintf'%x',~0
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Avoid the multiply:

say length sprintf "%b", ~0;;
64
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---

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.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

The j format is still architecture depending, as the others already showed. If your perl has 64bit ints (even if the poiters are just 32bit), does q (or Q) work for you? (for portability, do not forget < or >). That won't work on 32-bit-only perl builds.

$ perl -MDP -we'DHexDump pack "Q", 0x12345678'
0000  78 56 34 12 00 00 00 00                           xV4.....
$ perl -MDP -we'DHexDump pack "Q>", 0x12345678'
0000  00 00 00 00 12 34 56 78                           .....4Vx
$ perl -MDP -we'DHexDump pack "Q<", 0x12345678'
0000  78 56 34 12 00 00 00 00                           xV4.....
$ perl -V:uvsize
uvsize='8';

other perl

$ perl -V:uvsize
uvsize='4';
$ perl -wle'print length pack "Q", 3'
Invalid type 'Q' in pack at -e line 1.
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I had written once  use constant CAN_PACK_QUADS => !! eval { my $f = pack 'q'; 1 }; cause it dies when it can't

use constant MAXINT => ~0;
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I find: ~0 > 4294967295 to work and be simple/fast/understandable. Easier to follow at a glance than your pack, no time spent loading Config, no log() needed. If you use it a lot, make it a constant, e.g.

use constant MAXBITS => (~0 > 4294967295) ? 64 : 32;

A downside is that it assumes a 32-/64-bit world so isn't ready for 128-bit UVs if they every come. If you're already using the Config module or think it's more clear and don't care about the small load time, then I'd use that ($Config{uvsize}).

A warning on using ~0: don't use it in a place where bigint, bignum, or integer may be loaded, because it will be -1. This shouldn't be an issue inside your module, but something to be aware of.