This is very efficient in C. It works in Perl, but you'll have to time it and compare it against the other methods:

#! perl -slw
use strict;

sub nextPowerOfTwo {
    use integer;
    my $v = shift;
    $v--;
    $v |= $v >> 1;
    $v |= $v >> 2;
    $v |= $v >> 4;
    $v |= $v >> 8;
    $v |= $v >> 16;
    return ++$v;
}

print "$_ : ", nextPowerOfTwo( $_- 1 ) for map 1 << $_, 0 .. 63;

__END__
C:\test>nextPowerOfTwo.pl
1 : 0
2 : 1
4 : 4
8 : 8
16 : 16
32 : 32
64 : 64
128 : 128
256 : 256
512 : 512
1024 : 1024
2048 : 2048
4096 : 4096
8192 : 8192
16384 : 16384
32768 : 32768
65536 : 65536
131072 : 131072
262144 : 262144
524288 : 524288
1048576 : 1048576
2097152 : 2097152
4194304 : 4194304
8388608 : 8388608
16777216 : 16777216
33554432 : 33554432
67108864 : 67108864
134217728 : 134217728
268435456 : 268435456
536870912 : 536870912
1073741824 : 1073741824
2147483648 : 2147483648
4294967296 : 4294967296
8589934592 : 8589934592
17179869184 : 17179869184
34359738368 : 34359738368
68719476736 : 68719476736
137438953472 : 137438953472
274877906944 : 274877906944
549755813888 : 549755813888
1099511627776 : 1099511627776
2199023255552 : 2199023255552
4398046511104 : 4398046511104
8796093022208 : 8796093022208
17592186044416 : 17592186044416
35184372088832 : 35184372088832
70368744177664 : 70368744177664
140737488355328 : 140737488355328
281474976710656 : 281474976710656
562949953421312 : 562949953421312
1125899906842624 : 1125899906842624
2251799813685248 : 2251799813685248
4503599627370496 : 4503599627370496
9007199254740992 : 9007199254740992
18014398509481984 : 18014398509481984
36028797018963968 : 36028797018963968
72057594037927936 : 72057594037927936
144115188075855872 : 144115188075855872
288230376151711744 : 288230376151711744
576460752303423488 : 576460752303423488
1152921504606846976 : 1152921504606846976
2305843009213693952 : 2305843009213693952
4611686018427387904 : 4611686018427387904
9223372036854775808 : 9223372036854775808

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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.
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In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked

In reply to Re: reliable get position of leftmost bit in large integers by BrowserUk
in thread reliable get position of leftmost bit in large integers by wollmers

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