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In C programming, I have a set of information, and I have to ways of providing it to user:

  1. construct a data structure and provide it as an object.
  2. write a function to read them out and return them.

I used 2 for part of my project - some of my users expect to have those values available at compile-time, so function-like macros are needed, and the user code can work with both function-like macros and actual functions.

Here's my project, it's a cryptography library. And here's some background information.

Method 2 is used for obtaining working context size, key/block/output size for hash functions, AEAD ciphers, etc. and it work well for most symmetric-key algorithms. 2 is also used for asymmetric-key algorithms including key encapsulation mechnism and digital signature schemes.

Where compile-time and link/run-time deviates is when they're instantiated.

When an algorithm is instantiated at compile-time, a function-like macro is defined taking its parent algorithm, and specifying a parameter - take HMAC for example, HMAC is the parent algorithm, and a hash algorithm is the parameter.

When an algorithm is instantiated at link/run-time, a pointer to an object of type CryptoParam_t is specified as parameter.

But now, some of the information is known to be only available at run-time (or at least link-time) - asymmetric-key algorithm key-generation functions can only take CryptoParam_t objects is among the reasons. So is it better to just use 1? Is it an anti-pattern to use 2 now?

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  • It depends on the information. The repository is large, the question needs more scope. What kind of information are we talking about? Keep in mind that option 2 also sorts of includes option 1, you can use a unit test to ensure your runtime function can read static data from a known source.
    – Ccm
    Aug 5, 2023 at 11:56
  • @Ccm I've edited the question. One thing came into my mind is that, when using data objects, no "text-segment" code is needed, which can save some space if my project is actually used in some "free-standing" embedded hardwares.
    – DannyNiu
    Aug 5, 2023 at 12:11

1 Answer 1

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Ignoring for a moment that the library is free-standing. Obtaining public data through function is definitely NOT an anti-pattern.

For example, the public data is mutable, and the application is multi-threaded, functions can provide thread-safe ways to read, modify, and wait for change against the said data.

For the specific project mentioned in the OP, in addition to providing CryptoParam_t as public information objects, think what functions can add to it - instead of user duplicating codes that iterate over the algorithm instances table, a function can centralize that code, and provide easy way to

  • query for algorithm instances that provides a specific security level,
  • uses a specific family of underlaying algorithm (e.g. SHA-2 vs SHA-3/Keccak),
  • fed the hash algorithm instance, returning a suggested PRNG instance for use in e.g. RFC-6979-style deterministic signing.

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