Okay. If both arrays are sorted, you don't need a binary search.

You just move through them in parallel and you're done in a single pass:

#! perl -slw
use strict;

my @matches = map $_ * 10, 1 .. 10;
my @headers = map $_ * 5 +2, 0 .. 20;

my $hdr = 0;
for my $match ( @matches  ) {
    $hdr++ while $headers[ $hdr + 1 ] < $match;
    printf "match at %d in section from  %d - %d\n",
        $match, $headers[ $hdr ], $headers[ $hdr + 1 ] -1;
}

__END__
[16:20:40.99] c:\test>junk36
match at 10 in section from  7 - 11
match at 20 in section from  17 - 21
match at 30 in section from  27 - 31
match at 40 in section from  37 - 41
match at 50 in section from  47 - 51
match at 60 in section from  57 - 61
match at 70 in section from  67 - 71
match at 80 in section from  77 - 81
match at 90 in section from  87 - 91
match at 100 in section from  97 - 101
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