use strict;
use warnings;

sub lookup {
    my $v = shift;
    if( $v <        25000 ) { return        2500; }
    if( $v <        50000 ) { return        5000; }
    if( $v <       150000 ) { return       12500; }
    if( $v <       225000 ) { return       25000; }
    if( $v <       300000 ) { return       37500; }
    if( $v <       600000 ) { return       60000; }
    if( $v <      1200000 ) { return      120000; }
    if( $v <      3600000 ) { return      300000; }
    if( $v <      5400000 ) { return      600000; }
    if( $v <     10800000 ) { return      900000; }
    if( $v <     21600000 ) { return     1800000; }
    if( $v <     43200000 ) { return     3600000; }
    if( $v <     64800000 ) { return     7200000; }
    if( $v <    129600000 ) { return    10800000; }
    if( $v <    216000000 ) { return    21600000; }
    if( $v <    432000000 ) { return    43200000; }
    if( $v <    864000000 ) { return    86400000; }
    if( $v <   1728000000 ) { return   172800000; }
    if( $v <   3024000000 ) { return   345600000; }
    if( $v <   6048000000 ) { return   604800000; }
    if( $v <  12096000000 ) { return  1209600000; }
    if( $v <  31557600000 ) { return  2629800000; }
    if( $v <  63115200000 ) { return  5259600000; }
    if( $v <  78894000000 ) { return  7889400000; }
    if( $v < 157788000000 ) { return 15778800000; }
    else { return 31557600000; }
}

my @lookup_values = (
    [ 25000,        2500        ],
    [ 50000,        5000        ],
    [ 150000,       12500       ],
    [ 225000,       25000       ],
    [ 300000,       37500       ],
    [ 600000,       60000       ],
    [ 1200000,      120000      ],
    [ 3600000,      300000      ],
    [ 5400000,      600000      ],
    [ 10800000,     900000      ],
    [ 21600000,     1800000     ],
    [ 43200000,     3600000     ],
    [ 64800000,     7200000     ],
    [ 129600000,    10800000    ],
    [ 216000000,    21600000    ],
    [ 432000000,    43200000    ],
    [ 864000000,    86400000    ],
    [ 1728000000,   172800000   ],
    [ 3024000000,   345600000   ],
    [ 6048000000,   604800000   ],
    [ 12096000000,  1209600000  ],
    [ 31557600000,  2629800000  ],
    [ 63115200000,  5259600000  ],
    [ 78894000000,  7889400000  ],
    [ 157788000000, 15778800000 ],
);

sub guesslookup {
  my $v = shift;
  return 31557600000 if $v >= 157788000000;
  return 2500 if $v < 25000;
  my $guess = int( -15.35 + 1.535 * log $v ); # magic formula ;) have fun documenting!
  $guess++ while $lookup_values[$guess]->[0] <= $v;
  return $lookup_values[$guess]->[1];
}

for( my $test=0; $test<25; $test++ ) {
  for( my $offset=-1; $offset<=1; $offset++ ) {
    my $v = $lookup_values[$test]->[0] + $offset;
    my $org = lookup($v);
    my $new = guesslookup($v);
    print "Error: $test => $org : $new\n" if $org != $new;
  }
}