Subject: Re: [PATCH v2 02/13] sha1-file: provide functions to look up hash algorithms

From: SZEDER Gábor <[email-masked]>
Date: Wed, 17 Oct 2018 15:32:20 +0200

On Mon, Oct 15, 2018 at 02:18:49AM +0000, brian m. carlson wrote:
> There are several ways we might refer to a hash algorithm: by name, such
> as in the config file; by format ID, such as in a pack; or internally,
> by a pointer to the hash_algos array.  Provide functions to look up hash
> algorithms based on these various forms and return the internal constant
> used for them.  If conversion to another form is necessary, this
> internal constant can be used to look up the proper data in the
> hash_algos array.
> 
> Signed-off-by: brian m. carlson <[email-masked]>
> ---
>  hash.h      | 13 +++++++++++++
>  sha1-file.c | 21 +++++++++++++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/hash.h b/hash.h
> index 7c8238bc2e..90f4344619 100644
> --- a/hash.h
> +++ b/hash.h
> @@ -98,4 +98,17 @@ struct git_hash_algo {
>  };
>  extern const struct git_hash_algo hash_algos[GIT_HASH_NALGOS];
>  
> +/*
> + * Return a GIT_HASH_* constant based on the name.  Returns GIT_HASH_UNKNOWN if
> + * the name doesn't match a known algorithm.
> + */
> +int hash_algo_by_name(const char *name);
> +/* Identical, except based on the format ID. */
> +int hash_algo_by_id(uint32_t format_id);
> +/* Identical, except for a pointer to struct git_hash_algo. */
> +inline int hash_algo_by_ptr(const struct git_hash_algo *p)

This has to be declared as static, otherwise the linker will error out
when building without optimization:

    LINK git
libgit.a(commit-graph.o): In function `oid_version':
/home/szeder/src/git/commit-graph.c:48: undefined reference to `hash_algo_by_ptr'
libgit.a(hex.o): In function `hash_to_hex':
/home/szeder/src/git/hex.c:123: undefined reference to `hash_algo_by_ptr'
libgit.a(hex.o): In function `oid_to_hex':
/home/szeder/src/git/hex.c:128: undefined reference to `hash_algo_by_ptr'
collect2: error: ld returned 1 exit status
Makefile:2055: recipe for target 'git' failed
make: *** [git] Error 1

> +{
> +	return p - hash_algos;
> +}
> +
>  #endif
> diff --git a/sha1-file.c b/sha1-file.c
> index e29825f259..3a75d515eb 100644
> --- a/sha1-file.c
> +++ b/sha1-file.c
> @@ -122,6 +122,27 @@ const char *empty_blob_oid_hex(void)
>  	return oid_to_hex_r(buf, the_hash_algo->empty_blob);
>  }
>  
> +int hash_algo_by_name(const char *name)
> +{
> +	int i;
> +	if (!name)
> +		return GIT_HASH_UNKNOWN;
> +	for (i = 1; i < GIT_HASH_NALGOS; i++)
> +		if (!strcmp(name, hash_algos[i].name))
> +			return i;
> +	return GIT_HASH_UNKNOWN;
> +}
> +
> +int hash_algo_by_id(uint32_t format_id)
> +{
> +	int i;
> +	for (i = 1; i < GIT_HASH_NALGOS; i++)
> +		if (format_id == hash_algos[i].format_id)
> +			return i;
> +	return GIT_HASH_UNKNOWN;
> +}
> +
> +
>  /*
>   * This is meant to hold a *small* number of objects that you would
>   * want read_sha1_file() to be able to return, but yet you do not want