Instantiating globals in header files (FSW version)

[jphickey]

The FSW has a macro called "DECLARE_FIELD" which creates a constant at global scope:

CF/fsw/src/cf_field.h

Lines 54 to 55 in 7b99b91

	#define DECLARE_FIELD(NAME, NBITS, SHIFT) \
	static const CF_FIELD_FIELD NAME = {.shift = (SHIFT), .mask = ((1 << NBITS) - 1)};

The constant is scoped as "static" so it doesn't create a linker error, but it still creates a separate instance of this global variable for each time the header is included.

Confirmed by checking cf.so and observing that each of these 8 fields occur in the binary file 8 times:

CF/fsw/src/cf_cfdp_pdu.h

Lines 73 to 80 in 7b99b91

	DECLARE_FIELD(PDU_HDR_FLAGS_VERSION, 3, 5)
	DECLARE_FIELD(PDU_HDR_FLAGS_TYPE, 1, 4)
	DECLARE_FIELD(PDU_HDR_FLAGS_DIR, 1, 3)
	DECLARE_FIELD(PDU_HDR_FLAGS_MODE, 1, 2)
	DECLARE_FIELD(PDU_HDR_FLAGS_CRC, 1, 1)
	DECLARE_FIELD(PDU_HDR_FLAGS_RESERVED, 1, 0)
	DECLARE_FIELD(PDU_LENGTHS_ENTITY, 3, 4)
	DECLARE_FIELD(PDU_LENGTHS_TRANSACTION_SEQUENCE, 3, 0)

[jphickey]

Calling this a "bug" because space efficiency is one of the core requirements/expectations of this CF implementation, and this is not meeting that expectation. Plus, instantiating values from a header file is against most/all standards - it is not expected that simple inclusion of a header will cause extra memory to be allocated in the binary.

[jphickey]

This was partially addressed by #137, in that the DECLARE_FIELDS are only used in a single source file now, but it is not an ideal way to do it.

Better fix for this can be combined with #65, moving the field definitions into the codec code should achieve both.