#!/bin/bash

: <<=cut
=pod

=head1 NAME

rand - generate (pseudo-)random data


=head1 SYNOPSIS

B<rand> [-f FORMAT|--format FORMAT] [-s SEED|--seed SEED] [[I<from>] I<to>]


=head1 DESCRIPTION

B<rand> uses B<openssl> to generate pseudorandom data. Just like B<cat
/dev/urandom> it generates an infinite amount of data, but it is much
faster (400 MB/s on hardware from 2013).

The quality is lower as there are only 2^256 different tables (this is
still around the number of atoms in the visible universe).

If I<to> is given, numbers will be integers from 0 to I<to>.

If I<from> is also given, numbers will be integers from I<from> to I<to>.


=head1 OPTIONS

=over 4

=item B<--format> I<FORMAT>

=item B<-f> I<FORMAT>

Format number using I<FORMAT>. I<FORMAT> follows B<printf>s specification.


=item B<--seed> I<SEED>

=item B<-s> I<SEED>

Use SEED for random number generator for reproducible numbers.

=back


=head1 EXAMPLE

Overwrite a harddisk with random data:

  rand >/dev/sda


=head1 EXAMPLE

100 random numbers from 1000 to 1999:

  rand 1000 1999 | head -n 100


=head1 EXAMPLE

100 random numbers from 256 to 65535 in hex with 0s prepended:

  rand -f '%04x\n' 256 65535 | head -n 100


=head1 AUTHOR

Copyright (C) 2017-2020 Ole Tange,
http://ole.tange.dk and Free Software Foundation, Inc.


=head1 LICENSE

Copyright (C) 2012 Free Software Foundation, Inc.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
at your option any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.


=head1 DEPENDENCIES

B<rand> uses B<openssl>, B<perl>, and B<parallel>.


=head1 SEE ALSO

B<openssl>


=cut

randdata() {
    # Generate random 8-bit data by AES encrypting /dev/zero
    if [ "$seed" == "" ] ; then
	# use a random key
	key=$(openssl rand -hex 16)
	iv=$(openssl rand -hex 16)
    else
	# use seed from --seed
	key=$(echo "$seed" | openssl sha256 -hex | cut -d' ' -f2)
	iv=$(echo "$seed" | openssl sha512 -hex | cut -d' ' -f2)
    fi
    # single core = 743MiB/s
    < /dev/zero openssl enc -aes-128-ctr -K $key -iv $iv 2>/dev/null
    # single core = 184MiB/s
    # openssl rand 2000000000
}
export -f randdata

ints() {
    # Convert random data on stdin to numbers $from..$to in $fmt
    from=$1
    to=$2
    fmt="$3"
    # Allow up to 2^64
    perl -e '$diff='$to-$from'+1;
        $factor = 2**64/$diff;
        while(sysread(STDIN,$buf,65536)) {
            print map { sprintf("'"$fmt"'", int($_ / $factor) + '$from'); } unpack("Q*",$buf);
        }'
}
export -f ints

randints() {
    randdata | ints "$@"
}
export -f randints

# Default format of ints
fmt='%s\n'

while true; do
  case "$1" in
    -f | --fmt ) fmt="$2"; shift 2 ;;
    -s | --seed ) seed="$2"; shift 2 ;;
    -D | --debug ) debug=true; shift ;;
    -h | --help ) help=1; shift 2 ;;
    -- ) shift; break ;;
    * ) break ;;
  esac
done
qfmt="$(parallel --shellquote --shellquote ::: "$fmt")"

if [ "$seed" == "" ] ; then
    if [ "$1" == "" ] ; then
	# Boost performance by running 1 per CPU core
	eval parallel -u randdata ::: {1..$(parallel --number-of-threads)}
    else
	# $1 set => numerical
	if [ "$2" == "" ] ; then
	    # 0 .. $1
	    eval parallel -N0 --lb randints 0 $1 "$qfmt" ::: {1..$(parallel --number-of-threads)}
	else
	    # $1 .. $2
	    eval parallel -N0 --lb randints $1 $2 "$qfmt" ::: {1..$(parallel --number-of-threads)}
	fi
    fi
else
    if [ "$1" == "" ] ; then
	# Run a single instance
	randdata
    else
	# $1 set => numerical
	if [ "$2" == "" ] ; then
	    # 0 .. $1
	    randints 0 $1 "$fmt"
	else
	    # $1 .. $2
	    randints $1 $2 "$fmt"
	fi
    fi
fi