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=head1 TITLE
pack/unpack uncontrovercial enhancements
=head1 VERSION
Maintainer: Ilya Zakharevich <[EMAIL PROTECTED]>
Date: 16 September 2000
Mailing List: [EMAIL PROTECTED]
Number: 246
Version: 1
Status: Developing
=head1 ABSTRACT
This RFC proposes simple enhancements to templates of pack/unpack builtins.
These enhancements do not change the spirit of how pack/unpack is used.
The semantic is enhanced as much as possible under this constaint.
Additional changes to pack/unpack are listed in other proposals.
=head1 DESCRIPTION
The following additional constructs are allowed in pack()/unpack() TEMPLATEs:
=over 8
=item C<,> and C<;>
denotes the same as whitespace.
=item C<[4]>
denotes the same as C<4>, as in C<'i[4] S[4]'>.
=item C<[TEMPLATE]>
denotes the same as C<[$LEN]>; here $LEN is the length taken by the data
described by the template: C<$LEN = length pack TEMPLATE, @something>
(as far as it does not depend on @something, so C<A*> is prohibited).
This multiplier makes sense for byte-oriented types only. For example,
the middle part of C<'C[32] C[L8] C[64]'> will extract I<the substring> which
consists of 8 packed longs. Similarly, C<'C[32] x[L8] C[64]'> will skip
this substring.
=item C<x!LEN>
skip to offset divisible by C<LEN>. For example, C<'x![L]'> will align
to a long-compatible boundary.
=item C<W>
a BER encoded double.
=item C<w!>
a BER encoded "length", in other words, an integer encoded as BER lengths are.
=item C<(TEMPLATE)>
a group. May take a repeatition count either as C<(Ns)33> or as C<N/(Ns)>.
=item C<TEMPLATE1//TEMLATE2>
On unpack(): C<TEMPLATE1> extracts a number. This number specifies the number
of following bytes which the TEMPLATE2 should be applied to. (The difference
with C<TEMPLATE1/(TEMLATE2)> is that in the latter case the number extracted
by C<TEMPLATE1> is not the number of bytes, but the repetition count.)
During pack(), makes the opposite operation.
For example,
pack 'n//(A[4] C*)', 'a', 9..14
does the same as
pack 'n A[4] C*', 10, 'a', 9..14
(this is especially useful with the grouping proposals introduced in a
future RFC).
=item quad-formats
should work on 32-bit architectures too, using doubles instead (with a
possible precision loss).
=back
=head1 MIGRATION ISSUES
None.
=head1 IMPLEMENTATION
Straightforward.
=head1 REFERENCES
RFC142: Enhanced Pack/Unpack
