[% setvar title pack/unpack uncontrovercial enhancements %]
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pack/unpack uncontrovercial enhancements
Maintainer: Ilya Zakharevich <email@example.com> Date: 16 September 2000 Mailing List: firstname.lastname@example.org Number: 246 Version: 1 Status: Developing
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.
The following additional constructs are allowed in pack()/unpack() TEMPLATEs:
denotes the same as whitespace.
denotes the same as
4, as in
denotes the same as
[$LEN]; here $LEN is the length taken by the data
described by the template:
$LEN = length pack TEMPLATE, @something
(as far as it does not depend on @something, so
A* is prohibited).
This multiplier makes sense for byte-oriented types only. For example,
the middle part of
'C C[L8] C' will extract the substring which
consists of 8 packed longs. Similarly,
'C x[L8] C' will skip
skip to offset divisible by
LEN. For example,
'x![L]' will align
to a long-compatible boundary.
a BER encoded double.
a BER encoded "length", in other words, an integer encoded as BER lengths are.
a group. May take a repeatition count either as
(Ns)33 or as
TEMPLATE1 extracts a number. This number specifies the number
of following bytes which the TEMPLATE2 should be applied to. (The difference
TEMPLATE1/(TEMLATE2) is that in the latter case the number extracted
TEMPLATE1 is not the number of bytes, but the repetition count.)
During pack(), makes the opposite operation.
pack 'n//(A C*)', 'a', 9..14
does the same as
pack 'n A C*', 10, 'a', 9..14
(this is especially useful with the grouping proposals introduced in a future RFC).
should work on 32-bit architectures too, using doubles instead (with a possible precision loss).
RFC142: Enhanced Pack/Unpack