[PATCH v2 02/12] hash: create union for hash context allocation
- From
brian m. carlson <sandals@crustytoothpaste.net>
- Date
- Feb 1, 2018, 02:18 UTC
- Message-ID
- <20180201021848.533188-3-sandals@crustytoothpaste.net>
- In-Reply-To
- <20180201021848.533188-1-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. Use this union for defining the init, update, and final functions to avoid casts. 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 | 15 +++++++++------ sha1_file.c | 20 +++++++++----------- 2 files changed, 18 insertions(+), 17 deletions(-)
diff --git a/hash.h b/hash.h index 7122dea7b3..eb30f59be3 100644 --- a/hash.h +++ b/hash.h @@ -55,9 +55,15 @@ /* Number of algorithms supported (including unknown). */ #define GIT_HASH_NALGOS (GIT_HASH_SHA1 + 1) -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); +/* 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)(git_hash_ctx *ctx); +typedef void (*git_hash_update_fn)(git_hash_ctx *ctx, const void *in, size_t len); +typedef void (*git_hash_final_fn)(unsigned char *hash, git_hash_ctx *ctx); struct git_hash_algo { /* @@ -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..ec6ecea170 100644 --- a/sha1_file.c +++ b/sha1_file.c @@ -39,32 +39,32 @@ const struct object_id empty_blob_oid = { EMPTY_BLOB_SHA1_BIN_LITERAL }; -static void git_hash_sha1_init(void *ctx) +static void git_hash_sha1_init(git_hash_ctx *ctx) { - git_SHA1_Init((git_SHA_CTX *)ctx); + git_SHA1_Init(&ctx->sha1); } -static void git_hash_sha1_update(void *ctx, const void *data, size_t len) +static void git_hash_sha1_update(git_hash_ctx *ctx, const void *data, size_t len) { - git_SHA1_Update((git_SHA_CTX *)ctx, data, len); + git_SHA1_Update(&ctx->sha1, data, len); } -static void git_hash_sha1_final(unsigned char *hash, void *ctx) +static void git_hash_sha1_final(unsigned char *hash, git_hash_ctx *ctx) { - git_SHA1_Final(hash, (git_SHA_CTX *)ctx); + git_SHA1_Final(hash, &ctx->sha1); } -static void git_hash_unknown_init(void *ctx) +static void git_hash_unknown_init(git_hash_ctx *ctx) { die("trying to init unknown hash"); } -static void git_hash_unknown_update(void *ctx, const void *data, size_t len) +static void git_hash_unknown_update(git_hash_ctx *ctx, const void *data, size_t len) { die("trying to update unknown hash"); } -static void git_hash_unknown_final(unsigned char *hash, void *ctx) +static void git_hash_unknown_final(unsigned char *hash, git_hash_ctx *ctx) { die("trying to finalize unknown hash"); } @@ -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,