#! perl -sw
use 5.010;
use strict;
use Time::HiRes qw[ time ];

my $start = time;

my $recLen = 43;

open I, '<', '768941.dat' or die $!;
my $first = ( split ' ', scalar <I> )[ 0 ];

seek I, -$recLen, 2; ## SEEK_END
my $last  = ( split ' ', scalar <I> )[ 0 ];
say "$first - $last";

my $recs = tell( I ) / $recLen;
my $factor = $recs / ( $last - $first );

my $success = 0;
while( my $target = <> ) {
    chomp $target;

    warn "Input outside range"
        if $target > $last or $target < $first;

    my $offset = int( ( $target - $first ) * $factor ) * $recLen;

    my $rec;
    seek I, $offset, 0 or die "Seek failed\n";
    my $found = ( split ' ', $rec = <I> )[ 0 ];

    if( $found != $target ) {
        my $direction = $found < $target;
        $offset =  $direction ? $recLen : ( -$recLen * 2 );

        seek I, $offset, 1 or die "Seek failed" ## SEEK_CUR
            while ( $found = ( split ' ', $rec = <I> )[ 0 ] )
            and $direction ? ( $found < $target ) : ( $found > $target );
    }
    if( $found == $target ) {
        print "Found: $rec";
        ++$success;
    }
    else {
        warn "Target $target not found\n";
    }
}
close I;

printf STDERR "Found $success records in %.3f seconds\n", time() - $start;