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```{index} single: B::Op_private
```

# B::Op_private

B::Op\_private - OP op\_private flag definitions

## SYNOPSIS

```perl
use B::Op_private;

## flag details for bit 7 of OP_AELEM's op_private:
my $name  = $B::Op_private::bits{aelem}{7}; # OPpLVAL_INTRO
my $value = $B::Op_private::defines{$name}; # 128
my $label = $B::Op_private::labels{$name};  # LVINTRO

## the bit field at bits 5..6 of OP_AELEM's op_private:
my $bf  = $B::Op_private::bits{aelem}{6};
my $mask = $bf->{bitmask}; # etc
```

## DESCRIPTION

This module provides four global hashes:

```perl
%B::Op_private::bits
%B::Op_private::defines
%B::Op_private::labels
%B::Op_private::ops_using
```

which contain information about the per-op meanings of the bits in the
op\_private field.

### `%bits`

This is indexed by op name and then bit number (0..7). For single bit flags,
it returns the name of the define (if any) for that bit:

```perl
$B::Op_private::bits{aelem}{7} eq 'OPpLVAL_INTRO';
```

For bit fields, it returns a hash ref containing details about the field.
The same reference will be returned for all bit positions that make
up the bit field; so for example these both return the same hash ref:

```perl
$bitfield = $B::Op_private::bits{aelem}{5};
$bitfield = $B::Op_private::bits{aelem}{6};
```

The general format of this hash ref is

```perl
{
    # The bit range and mask; these are always present.
    bitmin        => 5,
    bitmax        => 6,
    bitmask       => 0x60,

    # (The remaining keys are optional)

    # The names of any defines that were requested:
    mask_def      => 'OPpFOO_MASK',
    baseshift_def => 'OPpFOO_SHIFT',
    bitcount_def  => 'OPpFOO_BITS',

    # If present, Concise etc will display the value with a 'FOO='
    # prefix. If it equals '-', then Concise will treat the bit
    # field as raw bits and not try to interpret it.
    label         => 'FOO',

    # If present, specifies the names of some defines and the
    # display labels that are used to assign meaning to particu-
    # lar integer values within the bit field; e.g. 3 is dis-
    # played as 'C'.
    enum          => [ qw(
                         1   OPpFOO_A  A
                         2   OPpFOO_B  B
                         3   OPpFOO_C  C
                     )],

};
```

### `%defines`

This gives the value of every `OPp` define, e.g.

```perl
$B::Op_private::defines{OPpLVAL_INTRO} == 128;
```

### `%labels`

This gives the short display label for each define, as used by `B::Concise`
and `perl -Dx`, e.g.

```perl
$B::Op_private::labels{OPpLVAL_INTRO} eq 'LVINTRO';
```

If the label equals '-', then Concise will treat the bit as a raw bit and
not try to display it symbolically.

### `%ops_using`

For each define, this gives a reference to an array of op names that use
the flag.

```perl
@ops_using_lvintro = @{ $B::Op_private::ops_using{OPp_LVAL_INTRO} };
```