RFC bit_vectors

["Alxneit-Kamber Ivo" <ivo dot alxneit at psi dot ch>]

Hi everybody,

attached please find an implementation of 'bit_vectors' (maybe bit
fields would be a better name) that might be an interesting addition to
GSL. 'bit_vectors' can be used similarly like a C bit field, only that
they grow and shrink dynamically depending on the number of bits in use.
Currently the user is limited to 'maximum(size_t)' bits (the bit number
is passed as size_t) or by the amount of memory available. Note,
however, that memory for all bits does not necessarily need to be
allocated because high bits that are either all 1 or 0 are stored as a
single implied bit.

I have implemented the following
	basic functions: init / free / set bit / clear bit / test bit
	utility functions: copy / print / fread / fwrite
	bit wise logical operators: and / or / xor / not
	shift operator: generic / left shift / right shift

'test.c' illustrates the use of bit_vectors. It is not intended to be a
strict verification er test of the code.

I am aware that one of the design criteria of GSL, using a preallocated
workspace instead of performing deep-allocations, is (deliberately)
violated. I thinks that this makes sense here. bit_vectors are, per
definition, infinitely long (within practical limits) and are intended
for situations where the user has no a-priory knowledge of how many
bits will be needed. Under normal circumstances (a few thousands bits
needed) allocation should never fail.

Comments, critisism wellcome.


regards
-- 
Dr. Ivo Alxneit
Laboratory for Solar Technology   phone: +41 56 310 4092
Paul Scherrer Institute             fax: +41 56 310 2688
CH-5232 Villigen                   http://solar.web.psi.ch
Switzerland                   gnupg key: 0x515E30C7

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