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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 C4, 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 CA* 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 Ithe substring which
consists of 8 packed longs. Similarly, C'C[32] x[L8] C[64]' will skip
this substring.
=item Cx!LEN
skip to offset divisible by CLEN. For example, C'x![L]' will align
to a long-compatible boundary.
=item CW
a BER encoded double.
=item Cw!
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 CN/(Ns).
=item CTEMPLATE1//TEMLATE2
On unpack(): CTEMPLATE1 extracts a number. This number specifies the number
of following bytes which the TEMPLATE2 should be applied to. (The difference
with CTEMPLATE1/(TEMLATE2) is that in the latter case the number extracted
by CTEMPLATE1 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
