Re: [PATCH v7 04/28] hash.h: provide constants for the hash IDs

From: Junio C Hamano <gitster@pobox.com>
Date: Apr 20, 2021, 19:49 UTC
Message-ID: <xmqqlf9c68iy.fsf@gitster.g>
In-Reply-To: <f0216ae20b6988514bdb60d8fff96e18c2ce9f1d.1618832277.git.gitgitgadget@gmail.com>

"Han-Wen Nienhuys via GitGitGadget" <gitgitgadget@gmail.com> writes:

Show 30 quoted lines

> From: Han-Wen Nienhuys <hanwen@google.com>
>
> This will simplify referencing them from code that is not deeply integrated with
> Git, in particular, the reftable library.
>
> Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
> ---
>  hash.h        | 6 ++++++
>  object-file.c | 6 ++----
>  2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/hash.h b/hash.h
> index 3fb0c3d4005a..b17fb2927711 100644
> --- a/hash.h
> +++ b/hash.h
> @@ -161,12 +161,18 @@ static inline int hash_algo_by_ptr(const struct git_hash_algo *p)
>  	return p - hash_algos;
>  }
>  
> +/* "sha1", big-endian */
> +#define GIT_SHA1_HASH_ID 0x73686131
> +
>  /* The length in bytes and in hex digits of an object name (SHA-1 value). */
>  #define GIT_SHA1_RAWSZ 20
>  #define GIT_SHA1_HEXSZ (2 * GIT_SHA1_RAWSZ)
>  /* The block size of SHA-1. */
>  #define GIT_SHA1_BLKSZ 64
>  
> +/* "s256", big-endian */
> +#define GIT_SHA256_HASH_ID 0x73323536

I agree that it makes sense to have symbolic constants defined in this file. These are values that fit in the ".format_id" member of "struct git_hash_algo", and it is preferrable to make sure that the names align (if I were designing in void, I would have called the member "algo_id" and made the constants GIT_(SHA1|SHA256)_ALGO_ID).

Brian? What's your preference ("I am fine to store HASH_ID in the '.format_id' member" is perfectly an acceptable answer).

Thanks.