in reply to Re^2: Read Bit String...!!!
in thread Read Bit String...!!!

Dropping to C is indeed an option, but bit twiddling should be pretty darn fast in Perl too. To generate 1 million random numbers and process their bits took 4 seconds: 

my $stime = time;

for (1..1_000_000) {
   my $i = rand(4294967295);
   while ($i) {
      $count++ if $i>>=2;
   }
}

my $etime = time;
print($etime-$stime, " seconds to count the $count 1s in 32_000_000 bi
+ts\n");

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4 seconds to count the 14665902 1s in 32_000_000 bits

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Update: Oops! if $i>>=2; should be if ($i>>=2) & 1; as per reply.

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Re^4: Read Bit String...!!!
by ysth (Canon) on Apr 10, 2008 at 04:24 UTC 
    my $stime = time;

for (1..1_000_000) {
   my $i = rand(4294967295);
   while ($i) {
      $count++ if $i>>=2;
   }
}

my $etime = time;
print($etime-$stime, " seconds to count the $count 1s in 32_000_000 bi
+ts\n");

    [download]
    That isn't counting 1s. It kind of assigns a score from 0 to 15 based on how big the number is, with most numbers scoring 15, and it is equivalent to 
       $count +=
      ($i > 2**2) +
      ($i > 2**4) +
      ($i > 2**6) +
      ...
      ($i > 2**26) +
      ($i > 2**28) +
      ($i > 2**30);

    [download]
    which on average gives 14 2/3. (3/4 of the numbers get 15, 3/4 of the remaining numbers get 14, 3/4 of the remaining numbers get 13, etc.)

    To count 1s (one of many ways): 

    do {
   ++$count if $i & 1;
} while $i >>= 1;

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