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    1 => 7,
    2 => 6,
    3 => 0,
    4 => 3,
    float32 => 6,
    float64 => 7,
    float16 => 6,
    uint8   => 0,
    int32   => 3
};
use constant DTYPE_PDL_TO_MX => {
    6 => 0,
    7 => 1,
    0 => 3,
    3 => 4,
};
use constant DTYPE_MX_TO_PERL => {
    0 => 'f',
    1 => 'd',
    2 => 'S',
    3 => 'C',
    4 => 'l',
    float32 => 'f',
    float64 => 'd',
    float16 => 'S',
    uint8   => 'C',
    int32   => 'l'
};
use constant GRAD_REQ_MAP => {
    null  => 0,
    write => 1,
    add   => 3
};

=head1 NAME

    AI::MXNet::Base - Helper functions

=head1 DEFINITION

    Helper functions

=head2 zip

    Perl version of for x,y,z in zip (arr_x, arr_y, arr_z)

    Parameters
    ----------
    $sub_ref, called with @_ filled with $arr_x->[$i], $arr_y->[$i], $arr_z->[$i]
    for each loop iteration.

    @array_refs
=cut

sub zip
{
    my ($sub, @arrays) = @_;
    my $len = @{ $arrays[0] };
    for (my $i = 0; $i < $len; $i++)
    {
        $sub->(map { $_->[$i] } @arrays);
    }
}

=head2 enumerate

    Same as zip, but the argument list in the anonymous sub is prepended
    by the iteration count.
=cut

sub enumerate
{
    my ($sub, @arrays) = @_;
    my $len = @{ $arrays[0] };
    zip($sub, [0..$len-1], @arrays);
}

=head2 product

    Calculates the product of the input agruments.
=cut

sub product
{
    my $p = 1;
    map { $p = $p * $_ } @_;
    return $p;
}

=head2 bisect_left

    https://hg.python.org/cpython/file/2.7/Lib/bisect.py
=cut

sub bisect_left
{
    my ($a, $x, $lo, $hi) = @_;
    $lo //= 0;
    $hi //= @{ $a };
    if($lo < 0)
    {
        Carp::confess('lo must be non-negative');
    }
    while($lo < $hi)
    {
        my $mid = int(($lo+$hi)/2);
        if($a->[$mid] < $x)
        {
            $lo = $mid+1;
        }
        else
        {
            $hi = $mid;
        }
    }
    return $lo;
}

=head2 pdl_shuffle

    Shuffle the pdl by the last dimension

    Parameters
    -----------
    PDL $pdl
    $preshuffle Maybe[ArrayRef[Index]], if defined the array elements are used
    as shuffled last dimension's indexes
=cut


sub pdl_shuffle
{
    my ($pdl, $preshuffle) = @_;
    my $c = $pdl->copy;
    my @shuffle = $preshuffle ? @{ $preshuffle } : shuffle(0..$pdl->dim(-1)-1);
    my $rem = $pdl->ndims-1;
    for my $i (0..$pdl->dim(-1)-1)
    {
        $c->slice(('X')x$rem, $i) .= $pdl->slice(('X')x$rem, $shuffle[$i])
    }
    $c;
}

=head2 assert

    Parameters