[PATCH 02/12] hash: create union for hash context allocation
- From
brian m. carlson <sandals@crustytoothpaste.net>
- Date
- Jan 28, 2018, 15:57 UTC
- Message-ID
- <20180128155722.880805-3-sandals@crustytoothpaste.net>
- In-Reply-To
- <20180128155722.880805-1-sandals@crustytoothpaste.net>
In various parts of our code, we want to allocate a structure representing the internal state of a hash algorithm. The original implementation of the hash algorithm abstraction assumed we would do that using heap allocations, and added a context size element to struct git_hash_algo. However, most of the existing code uses stack allocations and conversion would needlessly complicate various parts of the code. Add a union for the purpose of allocating hash contexts on the stack and a typedef for ease of use. Remove the ctxsz element for struct git_hash_algo, which is no longer very useful.
This does mean that stack allocations will grow slightly as additional hash functions are added, but this should not be a significant problem, since we don't allocate many hash contexts. The improved usability and benefits from avoiding dynamic allocation outweigh this small downside.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> --- hash.h | 9 ++++++--- sha1_file.c | 2 -- 2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/hash.h b/hash.h index 7122dea7b3..365846a6b5 100644 --- a/hash.h +++ b/hash.h @@ -55,6 +55,12 @@ /* Number of algorithms supported (including unknown). */ #define GIT_HASH_NALGOS (GIT_HASH_SHA1 + 1) +/* A suitably aligned type for stack allocations of hash contexts. */ +union git_hash_ctx { + git_SHA_CTX sha1; +}; +typedef union git_hash_ctx git_hash_ctx; + typedef void (*git_hash_init_fn)(void *ctx); typedef void (*git_hash_update_fn)(void *ctx, const void *in, size_t len); typedef void (*git_hash_final_fn)(unsigned char *hash, void *ctx); @@ -69,9 +75,6 @@ struct git_hash_algo { /* A four-byte version identifier, used in pack indices. */ uint32_t format_id; - /* The size of a hash context (e.g. git_SHA_CTX). */ - size_t ctxsz; - /* The length of the hash in binary. */ size_t rawsz; diff --git a/sha1_file.c b/sha1_file.c index 3da70ac650..e61d93a6e8 100644 --- a/sha1_file.c +++ b/sha1_file.c @@ -75,7 +75,6 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { 0x00000000, 0, 0, - 0, git_hash_unknown_init, git_hash_unknown_update, git_hash_unknown_final, @@ -86,7 +85,6 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = { "sha-1", /* "sha1", big-endian */ 0x73686131, - sizeof(git_SHA_CTX), GIT_SHA1_RAWSZ, GIT_SHA1_HEXSZ, git_hash_sha1_init,