hash: create union for hash context allocation
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>
diff --git a/hash.h b/hash.h
index 7122dea..eb30f59 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;
