int uv_fits_double(UV arg) {

  if(arg < 9007199254740993)
    return 1;

  while(!(arg & 1)) {
    arg >>= 1;
    if(arg < 9007199254740993) return 1;
  }

  return 0;
} 

##</code><code>##

sub uv_fits_double {

  my $arg = shift;

  return 1 if $arg < 9007199254740993;

  while(!($arg & 1)) {
    $arg >>= 1;
    return 1 if $arg < 9007199254740993;
  }

  return 0;
} 

##</code><code>##

use strict;
use warnings;
use Config;

die "This script not meant for this perl configuration"
  unless $Config{ivsize} == $Config{nvsize};

# The integer  value 2251799813685249 is
# representable exactly as a double.
# Therefore 2251799813685249 * (2 ** 10)
# is exactly representable as a double, 
# since 10 is well within the allowable 
# exponent range.
# 2251799813685249 * (2 ** 10) is also
# within the bounds of allowable integer
# values.

my $fits_d = 2305843009213694976; # 2251799813685249 * (2 ** 10)
my $no_fits_d = $fits_d + (2 ** 6);

print uv_fits_double(2251799813685249);    # fits
print uv_fits_double($fits_d);             # fits
print uv_fits_double($no_fits_d);          # doesn't fit
print uv_fits_double($fits_d + (2 ** 15)); # fits
print "\n";


sub uv_fits_double {
  my $arg = shift;

  return 1 if $arg < 9007199254740993;

  while(!($arg & 1)) {
    $arg >>= 1;
    return 1 if $arg < 9007199254740993;
  }

  return 0;
} 

__END__

Should output 1101
The 4th value fits, even though it's greater
than the 3rd value (which doesn't fit).