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hash: create union for hash context allocation

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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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
brian m. carlson 2018-02-01 02:18:38 +00:00 committed by Junio C Hamano
parent 164e716330
commit ac73cedff0
2 changed files with 18 additions and 17 deletions
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15
hash.h
View File

@ -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;

20
sha1_file.c
View File

@ -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,