|Subject:||Re: [potluck dish] the (potluck struct) module|
|Date:||Tue, 16 Feb 2016 05:53:32 -0800|
|First message got garbled. Redo:|
If you have used the Python struct module then this will look familiar.
Otherwise, check out https://docs.python.org/2/library/struct.html
Attached are three files:
* struct.scm: the source code
* struct.texi: documentation
* struct.test: test code
The '(potluck struct)' module provides procedures for packing and
unpacking scheme data to and from bytevectors based on a format string.
(use-modules (potluck struct))
;; pack two unsigned shorts and a double float in big endian order
(define data (pack ">2Hd" 3 22 34.0))
(write data) (newline)
#vu8(0 3 0 22 64 65 0 0 0 0 0 0)
;; verify using unpack
(write (unpack ">2Hd" data)) (newline)
(3 22 34.0)
-- Scheme Procedure: pack format vals ...
Return a bytevector that contains encoded data from VALS, based on
the string FORMAT.
-- Scheme Procedure: unpack format bvec
Return a list of scheme objects decoded from the bytevector BVEC,
based on the string FORMAT.
-- Scheme Procedure: packed-size format
Return the number of bytes represented by the string FORMAT.
The _format_ string used for PACK and UNPACK is constructed as a
sequence of digits, representing a repeat count, and codes, representing
the binary content.
The string may optionally begin with a special character that represents
= native endianness
! network order -- i.e., big-endian
Type codes used in the format string are interpreted as follows:
x blank byte
c 8-bit character
b signed 8-bit integer
B unsigned 8-bit integer
h signed 16-bit integer
H unsigned 16-bit integer
i signed 32-bit integer
I unsigned 32-bit integer
l signed 32-bit integer
L unsigned 32-bit integer
q signed 64-bit integer
Q unsigned 64-bit integer
f 32-bit IEEE floating point
d 64-bit IEEE floating point
The following issues remain to be addressed:
'pack' assumes that the string length in the format is the same as
in the passed string. Non-conformance is not trapped as an error.
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