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ttaylorrgitster
ttaylorr
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hash.h: scaffolding for _fast hashing variants
Git's default SHA-1 implementation is collision-detecting, which hardens us against known SHA-1 attacks against Git objects. This makes Git object writes safer at the expense of some speed when hashing through the collision-detecting implementation, which is slower than non-collision detecting alternatives. Prepare for loading a separate "fast" SHA-1 implementation that can be used for non-cryptographic purposes, like computing the checksum of files that use the hashwrite() API. This commit does not actually introduce any new compile-time knobs to control which implementation is used as the fast SHA-1 variant, but does add scaffolding so that the "git_hash_algo" structure has five new function pointers which are "fast" variants of the five existing hashing-related function pointers: - git_hash_init_fn fast_init_fn - git_hash_clone_fn fast_clone_fn - git_hash_update_fn fast_update_fn - git_hash_final_fn fast_final_fn - git_hash_final_oid_fn fast_final_oid_fn The following commit will introduce compile-time knobs to specify which SHA-1 implementation is used for non-cryptographic uses. Signed-off-by: Taylor Blau <[email protected]> Signed-off-by: Junio C Hamano <[email protected]>
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‎hash.h‎

Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -44,14 +44,32 @@
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#define platform_SHA1_Final SHA1_Final
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#endif
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#ifndef platform_SHA_CTX_fast
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# define platform_SHA_CTX_fast platform_SHA_CTX
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# define platform_SHA1_Init_fast platform_SHA1_Init
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# define platform_SHA1_Update_fast platform_SHA1_Update
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# define platform_SHA1_Final_fast platform_SHA1_Final
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# ifdef platform_SHA1_Clone
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# define platform_SHA1_Clone_fast platform_SHA1_Clone
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# endif
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#endif
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#define git_SHA_CTX platform_SHA_CTX
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#define git_SHA1_Init platform_SHA1_Init
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#define git_SHA1_Update platform_SHA1_Update
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#define git_SHA1_Final platform_SHA1_Final
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#define git_SHA_CTX_fast platform_SHA_CTX_fast
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#define git_SHA1_Init_fast platform_SHA1_Init_fast
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#define git_SHA1_Update_fast platform_SHA1_Update_fast
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#define git_SHA1_Final_fast platform_SHA1_Final_fast
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#ifdef platform_SHA1_Clone
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#define git_SHA1_Clone platform_SHA1_Clone
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#endif
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#ifdef platform_SHA1_Clone_fast
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# define git_SHA1_Clone_fast platform_SHA1_Clone_fast
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#endif
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#ifndef platform_SHA256_CTX
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#define platform_SHA256_CTX SHA256_CTX
@@ -81,6 +99,13 @@ static inline void git_SHA1_Clone(git_SHA_CTX *dst, const git_SHA_CTX *src)
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memcpy(dst, src, sizeof(*dst));
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}
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#endif
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#ifndef SHA1_NEEDS_CLONE_HELPER_FAST
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static inline void git_SHA1_Clone_fast(git_SHA_CTX_fast *dst,
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const git_SHA_CTX_fast *src)
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{
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memcpy(dst, src, sizeof(*dst));
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}
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#endif
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#ifndef SHA256_NEEDS_CLONE_HELPER
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static inline void git_SHA256_Clone(git_SHA256_CTX *dst, const git_SHA256_CTX *src)
@@ -178,6 +203,8 @@ enum get_oid_result {
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/* A suitably aligned type for stack allocations of hash contexts. */
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union git_hash_ctx {
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git_SHA_CTX sha1;
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git_SHA_CTX_fast sha1_fast;
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git_SHA256_CTX sha256;
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};
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typedef union git_hash_ctx git_hash_ctx;
@@ -222,6 +249,21 @@ struct git_hash_algo {
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/* The hash finalization function for object IDs. */
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git_hash_final_oid_fn final_oid_fn;
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/* The fast / non-cryptographic hash initialization function. */
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git_hash_init_fn fast_init_fn;
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/* The fast / non-cryptographic hash context cloning function. */
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git_hash_clone_fn fast_clone_fn;
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/* The fast / non-cryptographic hash update function. */
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git_hash_update_fn fast_update_fn;
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/* The fast / non-cryptographic hash finalization function. */
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git_hash_final_fn fast_final_fn;
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/* The fast / non-cryptographic hash finalization function. */
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git_hash_final_oid_fn fast_final_oid_fn;
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/* The OID of the empty tree. */
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const struct object_id *empty_tree;
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‎object-file.c‎

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Original file line numberDiff line numberDiff line change
@@ -115,6 +115,33 @@ static void git_hash_sha1_final_oid(struct object_id *oid, git_hash_ctx *ctx)
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oid->algo = GIT_HASH_SHA1;
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}
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static void git_hash_sha1_init_fast(git_hash_ctx *ctx)
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{
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git_SHA1_Init_fast(&ctx->sha1_fast);
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}
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static void git_hash_sha1_clone_fast(git_hash_ctx *dst, const git_hash_ctx *src)
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{
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git_SHA1_Clone_fast(&dst->sha1_fast, &src->sha1_fast);
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}
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static void git_hash_sha1_update_fast(git_hash_ctx *ctx, const void *data,
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size_t len)
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{
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git_SHA1_Update_fast(&ctx->sha1_fast, data, len);
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}
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static void git_hash_sha1_final_fast(unsigned char *hash, git_hash_ctx *ctx)
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{
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git_SHA1_Final_fast(hash, &ctx->sha1_fast);
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}
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static void git_hash_sha1_final_oid_fast(struct object_id *oid, git_hash_ctx *ctx)
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{
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git_SHA1_Final_fast(oid->hash, &ctx->sha1_fast);
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memset(oid->hash + GIT_SHA1_RAWSZ, 0, GIT_MAX_RAWSZ - GIT_SHA1_RAWSZ);
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oid->algo = GIT_HASH_SHA1;
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}
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static void git_hash_sha256_init(git_hash_ctx *ctx)
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{
@@ -189,6 +216,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
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.update_fn = git_hash_unknown_update,
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.final_fn = git_hash_unknown_final,
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.final_oid_fn = git_hash_unknown_final_oid,
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.fast_init_fn = git_hash_unknown_init,
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.fast_clone_fn = git_hash_unknown_clone,
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.fast_update_fn = git_hash_unknown_update,
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.fast_final_fn = git_hash_unknown_final,
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.fast_final_oid_fn = git_hash_unknown_final_oid,
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.empty_tree = NULL,
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.empty_blob = NULL,
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.null_oid = NULL,
@@ -204,6 +236,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
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.update_fn = git_hash_sha1_update,
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.final_fn = git_hash_sha1_final,
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.final_oid_fn = git_hash_sha1_final_oid,
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.fast_init_fn = git_hash_sha1_init_fast,
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.fast_clone_fn = git_hash_sha1_clone_fast,
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.fast_update_fn = git_hash_sha1_update_fast,
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.fast_final_fn = git_hash_sha1_final_fast,
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.fast_final_oid_fn = git_hash_sha1_final_oid_fast,
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.empty_tree = &empty_tree_oid,
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.empty_blob = &empty_blob_oid,
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.null_oid = &null_oid_sha1,
@@ -219,6 +256,11 @@ const struct git_hash_algo hash_algos[GIT_HASH_NALGOS] = {
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.update_fn = git_hash_sha256_update,
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.final_fn = git_hash_sha256_final,
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.final_oid_fn = git_hash_sha256_final_oid,
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.fast_init_fn = git_hash_sha256_init,
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.fast_clone_fn = git_hash_sha256_clone,
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.fast_update_fn = git_hash_sha256_update,
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.fast_final_fn = git_hash_sha256_final,
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.fast_final_oid_fn = git_hash_sha256_final_oid,
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.empty_tree = &empty_tree_oid_sha256,
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.empty_blob = &empty_blob_oid_sha256,
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.null_oid = &null_oid_sha256,

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